Dr. Jeff Masters' WunderBlog

Xangsane intensifying rapidly just before landfall

By: JeffMasters, 10:41 PM GMT en Septiembre 30, 2006

Typhoon Xangsane is making landfall on the central coast of Vietnam in the next few hours. Unfortunately for Vietnam, the typhoon is making an impressive last-minute intensification spurt, with the cloud tops getting very cold and the eye shrinking to a very tiny size. See the animation of the IR satellite images for the storm from NOAA. Da Nang on the central coast of Vietnam has had its winds rise to 56 mph with higher gusts at last report, and may receive a direct hit from Xangsane with heavy damage. I hope they got everyone out! The rest of my blog is the same as this morning's below--

Vietnam has ordered mass evacuations of 200,000 coastal residents in the path of Xangsane. This is the largest evacuation in Vietnam for a typhoon in 30 years. Authorities are most concerned for the welfare of about 4,000 fisherman still at sea in the path of the typhoon; in May, 234 Vietnamese fishermen were killed or unaccounted for after Supertyphoon Chanchu passed east of Vietnam on its way to a landfall in China.

The Philippine Islands continue to clean up from Xangsane today, and the death toll stands at 94 with at least another 60 people missing. Over 15,000 homes were damaged or destroyed, and power is still out to 20% of the island of Luzon's 43 million people. The death toll from the storm was not as high as many other typhoons to strike the country in recent years, since Xangsane moved though fairly quickly--15 mph--and didn't have time to dump as much rain as usual for a typhoon. Peak rain amounts (Figure 1) were about 10 inches, and rainfall amounts closer to 15 inches are required to trigger the kinds of major flash flooding and mud slides that often kill so many in the Philippines.


Figure 1. Rainfall from Typhoon Xangsane over the Philippines as measured by NASA's TRMM satellite. 250mm is about 10 inches. Image credit: NASA TRMM Project.

Hurricane Isaac
Hurricane Isaac became the season's fifth hurricane this morning, thanks to some lighter wind shear, warmer waters, and moister air. Isaac has another day or two of favorable conditions before cooler waters and high wind shear weaken the hurricane. Isaac is expected to pass near southeast Newfoundland on Monday as a tropical storm with 55 mph winds.

Elsewhere in the tropics
A non-tropical low pressure system is expected to form in the mid-Atlantic south of the Azores Islands by Wednesday, and this system may make the transition to a tropical storm as it drifts south over the open Atlantic late in the week. There are no other threat areas to discuss--the tropical wave (97L) that we were tracking yesterday, north of Puerto Rico, has fallen apart.

I'll have an update Sunday morning.

Jeff Masters

Updated: 11:30 AM GMT en Octubre 01, 2006

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Typhoon Xangsane bears down on Vietnam

By: JeffMasters, 4:35 PM GMT en Septiembre 30, 2006

Vietnam has ordered mass evacuations of 200,000 coastal residents in the path of Typhoon Xangsane, now a very dangerous Category 3 typhoon over the South China Sea. This is the largest evacuation in Vietnam for a typhoon in 30 years. Xangsane is expected to hit Vietnam on Sunday morning as a major typhoon. Authorities are most concerned for the welfare of about 4,000 fisherman still at sea in the path of the typhoon; in May, 234 Vietnamese fishermen were killed or unaccounted for after Supertyphoon Chanchu passed east of Vietnam on its way to a landfall in China. Da Nang on the central coast of Vietnam has had its winds rise to 29 mph with higher gusts today, and may receive a direct hit from Xangsane.

The Philippine Islands continue to clean up from Xangsane today, and the death toll stands at 94 with at least another 60 people missing. Over 15,000 homes were damaged or destroyed, and power is still out to 20% of the island of Luzon's 43 million people. The death toll from the storm was not as high as many other typhoons to strike the country in recent years, since Xangsane moved though fairly quickly--15 mph--and didn't have time to dump as much rain as usual for a typhoon. Peak rain amounts (Figure 1) were about 10 inches, and rainfall amounts closer to 15 inches are required to trigger the kinds of major flash flooding and mud slides that often kill so many in the Philippines.


Figure 1. Rainfall from Typhoon Xangsane over the Philippines as measured by NASA's TRMM satellite. 250mm is about 10 inches. Image credit: NASA TRMM Project.

Hurricane Isaac
Hurricane Isaac became the season's fifth hurricane this morning, thanks to some lighter wind shear, warmer waters, and moister air. Isaac has another day or two of favorable conditions before cooler waters and high wind shear weaken the hurricane. Isaac is expected to pass near southeast Newfoundland on Monday as a tropical storm with 55 mph winds.

Elsewhere in the tropics
A non-tropical low pressure system is expected to form in the mid-Atlantic south of the Azores Islands by Wednesday, and this system may make the transition to a tropical storm as it drifts south over the open Atlantic late in the week. There are no other threat areas to discuss--the tropical wave (97L) that we were tracking yesterday, north of Puerto Rico, has fallen apart.

I'll have an update Sunday morning.

Jeff Masters

Updated: 9:01 PM GMT en Septiembre 30, 2006

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Puerto Rico disturbance weakens; powerful Typhoon Xangsane threatens Vietnam

By: JeffMasters, 2:42 PM GMT en Septiembre 29, 2006

The tropical wave over the northernmost Lesser Antilles Islands (designated 97L by the NHC yesterday) has weakened. The wave is north of Puerto Rico this morning, and could bring some heavy rains to that island today. The system is very small and disorganized, and the 10-15 knots of wind shear over it will probably not allow such a small system to develop. You can follow the progress of 97L today on long range Puerto Rico radar.


Figure 1. Preliminary models tracks for Invest 97L.

Typhoon Xangsane
The Philippine Islands continue to count the dead and assess the damage left by Typhoon Xangsane, which roared over the main Philippine Island of Luzon Wednesday, passing directly over the capital city of Manila. At least 60 are dead and another 60 missing, with many hard-hit areas still to be heard from, due to failed communications and washed out roads. The majority of the victims died in mudslides, flash floods, and building collapses. Xangsane cut power to all 43 million people on the island of Luzon, making it one of the most extensive blackouts due to natural disaster in world history. Power had been restored to about 40% of the island this morning. Xangsane (from the Laotian word for Elephant) hit as a Category 4 typhoon with 145 mph winds before weakening during its passage over land. It has reintensified today into a Category 4 typhoon over the South China Sea, and is expected to deliver a heavy blow to Vietnam on Sunday.


Figure 2. Rainfall from Typhoon Xangsane over the Philippines as measured by NASA's TRMM satellite. The pink color represents about ten inches of rain. Image credit: NASA TRMM Project.

Isaac
Tropical Storm Isaac continues to look unimpressive, thanks to dry air on the south side being drawn in, wind shear from an upper level low, and passage over some cool ocean waters stirred up by hurricanes Gordon and Helene. All of these influences should diminish a bit over the next day, which may allow Isaac the opportunity to do some modest intensification. The storm is not a threat to any land areas, and should recurve out to sea this weekend.

Elsewhere in the tropics
A strong cold front has pushed off the North American coast, and is serving as the focus of some thunderstorm development from the Bahamas southwestward through the waters south of Florida. We'll have to watch this region over the coming days for some possible development. However, the computer models are no longer forecasting development along this old front.

Next week, a non-tropical low pressure system is expected to form in the mid-Atlantic south of the Azores Islands, and this system may make the transition to a tropical storm like Delta, Epsilon, and Zeta did last year.

I'll have an update Saturday morning, and I'll post my outlook for October on Monday. We might be done with landfalling hurricanes for the year!

Jeff Masters

Updated: 2:47 PM GMT en Septiembre 29, 2006

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New disturbance affecting Lesser Antilles; Typhoon Xangsane batters the Philippines

By: JeffMasters, 1:56 PM GMT en Septiembre 28, 2006

A tropical wave moving through the northernmost Lesser Antilles Islands this morning has been declared "Invest 97L" by the National Hurricane Center. Although small, the wave has developed enough heavy thunderstorm activity to be of concern. The wave is moving west-northwest at 15 mph, and will bring heavy rains and gusty winds to Antigua, St. Maarten, and surrounding islands today, and Puerto Rico on Friday. Martinique radar shows a moderate area of heavy rain moving through the islands. Antigua has seen some heavy rain this morning and gusty winds. Winds shifted to southwesterly at 11am EDT this morning, indicating that a closed surface circulation may exist. QuikSCAT winds at 6:22am EDT this morning showed a large area of 20-25 mph winds under these thunderstorms, and a strong wind shift, but not a closed surface circulation. The wave is under about 10 knots of wind shear, and this shear is expected to remain below 15 knots the next two days. The low shear and warm waters the system is over may allow some continued development. The computer models are not tracking this system very well because it is so small, but it appears likely that the storm will pass just north of the Bahamas and then turn north. The storm will probably not hit the U.S. East Coast. The earliest this could become a tropical depression is Sunday.


Figure 1. Preliminary models tracks for Invest 97L.

Typhoon Xangsane
Typhoon Xangsane roared over the main Philippine Island of Luzon yesterday, passing directly over the capital city of Manila, home to 12 million people. Xangsane was rated as a Category 3 storm when it hit Manila, but winds of only Category 1 strength affected the city. The Manila airport recorded maximum sustained winds of 60 mph, gusting to 89 mph as the northern eyewall of Xangsane battered the city about noon local time. Manila passed into the calm of the eye, recording a pressure of 954 mb. Eleven deaths have been blamed on the typhoon so far, five of them from a mudslide in a mountainous area. Thirty people are missing in a dam collapse south of Manila. Xangsane's death toll is likely to go much higher when the area southeast of Manila where Xangsane made landfall as a Category 4 typhoon is heard from. Damage so far has been heavy, particularly to agriculture, and losses will likely reach several hundred million dollars. Xangsane did extensive damage to the power grid of Luzon, and the entire island experienced a blackout. Only 5% of the island has seen power restored thus far.

The last significant typhoon to affect Manila was 1995's Supertyphoon Angela, which killed 740, left 650,000 homeless, and caused severe damage to the agricultural areas surrounding the capital. Angela was one of 14 tropical storms or typhoons to affect the Philippines that year. So far this year, four typhoons have affected the Philippines. Interaction with land has weakened Xangsane on its passage over the Philippine Islands, but the typhoon should intensify once more this weekend into a major typhoon before hitting Vietnam on Sunday.


Figure 1. Typhoon Xangsane at landfall in the Philippines. Image credit: NASA.

Isaac is born
Tropical Storm Isaac formed over the waters southeast of Bermuda this morning. QuikSCAT wind data from 4:43am EDT this morning showed numerous wind barbs of tropical storm strength, which was given as the justification ofr upgrading the storm at 11am today. However, satellite imagery this morning shows a decrease in the amount and intensity of the thunderstorm activity near the center. Isaac is not a classic tropical storm, and may be more properly called a subtropical storm--one that is a hybrid between a true tropical storm and an extratropical storm. An upper level low is bringing about 10 knots of shear over the storm and some dry air into the center from the southwest. These negative influences are expected to decrease over the next 48 hours, which should allow slow intensification. All of the models predict that Isaac will turn north and recurve out to sea, and will not be a threat to any land areas.

Elsewhere in the tropics
The Western Caribbean near the Yucatan Peninsula could see some development early next week, when a strong cold front is expected to push off the East Coast of the U.S. and stall out over this region. The NOGAPS model continues to forecast tropical storm development here next week.

An area of heavy thunderstorms associated with a tropical wave near 9N 50W, about 500 miles east of the South American coast, is moving west at 15 mph. This wave is under about 10 knots of shear, but is disorganized, and I don't expect it to develop.

I'll have an update Friday morning.
Jeff Masters

Updated: 3:29 PM GMT en Septiembre 28, 2006

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Typhoon Xangsane whallops the Philippines; new disturbance approaching Lesser Antilles Islands

By: JeffMasters, 2:22 PM GMT en Septiembre 27, 2006

Typhoon Xangsane, potentially the most dangerous tropical cyclone to affect the world this year, is battering the Philippine Islands today with Category 4 winds. Xangsane was a mere tropical storm yesterday, and was expected to hit the Philippines as a tropical storm or weak Category 1 typhoon at worst. Xangsane confounded the experts and put on a remarkable intensification spurt that brought it from tropical storm strength to a Category 4 typhoon in just 24 hours. The intensification was not expected, since the typhoon's circulation hugged the coast for much of this period.


Figure 1. Typhoon Xangsane at landfall in the Philippines. Image credit: Navy Research Lab.

The Philippines are very vulnerable to high death tolls from major typhoons, due to the high terrain that spawns deadly mudslides and floods. Xangsane is forecast to pass over the capital, Manila--the most heavily populated area of the country. These factors, plus the unpreparedness of the population due to the poor forecasts of Xangsane's intensification, make Xangsane a very dangerous storm for the Philippines. The last significant typhoon to affect Manila was 1995's Supertyphoon Angela, which killed 740, left 650,000 homeless, and caused severe damage to the agricultural areas surrounding the capital. Angela was one of 14 tropical storms or typhoons to affect the typhoon-prone Philippines that year.

Wind reports from Legospi and Catanduanes showed sustained winds of 63 mph and 45 mph, respectively so far today, with higher gusts. The winds have not yet picked up at the capital of Manila, where Xangsane is expected to pass Friday as a Category 2 typhoon. Interaction with land should weaken Xangsane on its passage over the Philippine Islands, but the typhoon should intensify once more this weekend into a major typhoon before hitting Vietnam.

New threat approaching Lesser Antilles Islands
A new area of concern has developed this morning near 17N 58W, about 500 miles east of the northernmost Lesser Antilles Islands, in association with a tropical wave moving west-northwest at 15 mph. The wave has developed a sharp increase in its heavy thunderstorm activity, and there are signs of a surface circulation in visible satellite imagery. Winds at a buoy at 16N, 58W, just to the south of the disturbance, have gone from northeast to north-northwest in the past few hours, signifying that this disturbance might have a closed circulation. Unfortunately, this morning's QuikSCAT pass missed the disturbance, and we'll have to wait until about 8pm EDT for a new pass. The disturbance will bring showers and gusty winds to the northern Lesser Antilles Islands Friday morning. The disturbance is under about 10 knots of wind shear, and the shear is expected to remain at 10 knots or below the next few days. This may allow some development, and we will need to keep a close eye on this wave. I imagine it will end up recurving between Bermuda and the U.S. East Coast, but it is too early to be confident of this.

We also need to watch the cloud-covered areas of the ocean surrounding the U.S. where cold fronts stall out over the next week. One such area to watch is off the North Carolina Outer Banks today, where a tropical low could develop and scoot quickly northeastward out to sea. The Western Caribbean near the Yucatan Peninsula could see some development early next week, when a strong cold front is expected to push off the East Coast of the U.S. and stall out over this region.

Disturbance 96L near tropical depression strength
The tropical wave (96L) we've been watching, at 26N 52W, about 850 miles east-northeast of the northern Lesser Antilles Islands, is near tropical depression strength. Wind shear has dropped from 20 knots yesterday to 15 knots today, which has allowed more heavy thunderstorm activity to build to the east of the center of circulation. The QuikSCAT pass from 5am EDT this morning showed winds of 25-30 knots (30-35 mph) in some of the heavier squalls. The storm is in a moist environment, the ocean beneath is warm, and I do expect that the shear will remain low enough to allow 96L to develop into a tropical depression in the next day or two, as forecast by the Canadian and GFDL models. All of the models predict that 96L will turn north and recurve out to sea, and will not be a threat to any land areas.


Figure 1. Preliminary models tracks for Invest 96L.

I'll have an update Thursday morning, or later today if the new wave approaching the Lesser Antilles islands looks significant.

Jeff Masters

Updated: 2:51 PM GMT en Septiembre 27, 2006

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96L disturbance hanging in there; F4 tornado confirmed in Missouri

By: JeffMasters, 1:52 PM GMT en Septiembre 26, 2006

Well, it sure was great to watch a football game in the New Orleans Superdome last night, and not worry about a hurricane threatening the coast! The hurricane season of 2006 has been exceptionally kind to us by the standards of the past ten years, are there is nothing out there today that causes me any concern. The tropical wave (96L) we've been watching, about 900 miles east-northeast of the northern Lesser Antilles Islands, does has the potential to develop into a tropical depression, but is not expected to threaten any land areas. Wind shear has dropped from 30 knots yesterday to 20 knots today, and the system has been able to maintain more heavy thunderstorm activity near its center this morning. The storm is in a moist environment, and the ocean beneath is warm. The Canadian model is still the only model that develops the system into a tropical storm, but it appears that wind shear will drop another 5 knots over the next two days, potentially allowing 96L to organize into a tropical depression. Bermuda will need to keep an eye on this system, but I expect it will recurve out to sea before reaching the island.

Elsewhere in the tropical Atlantic, it's time to start watching the cloud-covered areas of the ocean surrounding the U.S. where cold fronts stall out. One such area to watch is off the North Carolina Outer Banks on Wednesday, when a tropical low could develop and scoot quickly northeastward out to sea. The more dangerous possibility is in the Gulf of Mexico or Western Caribbean near the Yucatan Peninsula early next week. A strong cold front is expected to push off the East Coast of the U.S. this weekend and stall over the Gulf of Mexico or Western Caribbean. The past few runs of the NOGAPS model have been predicting that if this front stalls out over the Western Caribbean, it could serve as a genesis area for a tropical storm. None of the other models are picking up on this, but this is a typical type of development we see in this region in October.


Figure 1. Preliminary models tracks for Invest 96L.

F4 tornado confirmed in Missouri
The National Weather Service confirmed yesterday that the second violent F4 tornado of the year occurred Friday. The 350 yard-wide tornado ripped through Crosstown, MO, injuring five. F4 tornadoes have winds speeds of 207-260 mph (there have been no F5 tornadoes with winds in excess of 260 mph reported in the U.S. since 1999). The weekend severe weather outbreak was the second largest of the year, with 59 tornadoes (including 40 on September 22). The other F4 tornado of 2006 also affected Missouri, when Monroe City got hit on March 12 as part of the biggest severe weather outbreak of the year--84 tornadoes over a 3-day span.

I'll have an update Wednesday morning.
Jeff Masters

Tornado

Updated: 6:49 PM GMT en Enero 05, 2012

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Quiet tropics; Superdome reopens!

By: JeffMasters, 1:29 PM GMT en Septiembre 25, 2006

The tropical wave (96L) we've been watching, about 1000 miles east of the northern Lesser Antilles Islands, is struggling against 20-30 knots of wind shear this morning. The shear has reduced the amount of heavy thunderstorm activity, and it appears less likely that 96L can organize into a tropical depression. The Canadian model is now the only model developing the system; the other models all indicate that wind shear will remain too high to allow development. The system will move northwestwards towards Bermuda, and probably turn to the north late this week before it reaches the island.


Figure 1. Preliminary models tracks for Invest 96L.

Superdome reopens tonight
A major milestone in the Hurricane Katrina recovery efforts occurs tonight, when the New Orleans Superdome reopens. After nearly $200 million in repairs and renovations, the Superdome is ready to host a football game between the New Orleans Saints and Atlanta Falcons. The bands U2 and Green Day will be on hand to celebrate the event, and former president George H.W. Bush will perform the opening coin flip. While New Orleans and the entire coast of Louisiana and Mississippi devastated by Katrina and Rita still have a formidable recovery effort ahead, the reopening of the Superdome will provide a wonderful psychological boost. Residents of the region can also take cheer that the hurricane season of 2006 has no plans to spoil the event. Recall that last year at this time, Hurricane Rita had just powered ashore in Southwest Louisiana, and the season still had 11 more named storms coming. The tropics have gone very quiet this year, and there are no signs that the coming weeks will bring any major hurricanes to the Atlantic.

Weekend severe weather
The first major Fall severe weather outbreak occurred over the weekend over portions of the Midwestern U.S. Five people were injured Friday afternoon in Perry County, Missouri, when a tornado 350 yards in diameter ripped through Crosstown. Preliminary assessments by NWS survey teams estimated that this was an F3 or stronger tornado with 200 mph winds.

The same storm system also brought flooding rains to Arkansas, Illinois, Indiana, Kentucky, Missouri and Tennessee on Friday and Saturday that were blamed for at least nine deaths. Mayfield, KY reported 13.82 inches of rain in the deluge.

I'll have an update Tuesday morning.
Jeff Masters

Updated: 1:55 PM GMT en Septiembre 25, 2006

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Disturbance 96L near tropical depression strength

By: JeffMasters, 4:12 PM GMT en Septiembre 24, 2006

A tropical wave (dubbed "96L" by NHC) is in the mid-Atlantic, 1200 miles east of the northernmost Lesser Antilles Islands. The storm has developed a well-defined circular rotation visible on visible satellite animations, and is close to tropical depression status. QuikSCAT winds from this morning's 4:45am EDT pass were 25-35 mph in a few isolated patches. About 20 knots of winds shear from the west is keeping the heavy thunderstorm activity of 96L confined to the east side of its circulation. If this shear relaxes for 12 or so hours, the storm has a chance at organizing into a tropical depression.

The computer models indicate that wind shear may drop enough to allow 96L to organize into a weak tropical storm, but none of the models are forecasting a hurricane. The storm is currently drifting slowly to the northwest. As the remains of Hurricane Helene race off to the northeast over the next few days, the Bermuda High will re-establish itself and a high pressure ridge will build in, forcing 96L to the west-northwest. The system could threaten Bermuda around Friday. However, I think it is likely that a trough of low pressure will recurve 96L northwards and out to sea before it reaches Bermuda.


Figure 1. Preliminary model tracks for Invest 96L.

Elsewhere in the tropics
Hurricane Helene has completed its transition to an extratropical storm, and its remnants may bring high winds and heavy rain to Ireland on Wednesday. A few of the computer models are forecasting that a new tropical storm will develop between Africa and the Lesser Antilles later this week. Any development in this region would likely recurve northwards out to sea.

I'll have an update Monday morning.
Jeff Masters

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New disturbance slowly organizing, but no threat to land

By: JeffMasters, 3:38 PM GMT en Septiembre 23, 2006

A tropical wave featuring a broad surface circulation about 1100 miles west of the Cape Verde Islands has become better organized since yesterday. There is more heavy thunderstorm activity, and the cloud pattern is a bit more circular. QuikSCAT winds from this morning's 5:11am EDT pass were 25-35 mph in a few isolated patches. This system (96L) probably needs at least another two days to organize into a tropical depression as it moves northwest over the open Atlantic. The storm is moving towards a weakness in the Bermuda High created by Hurricane Helene. Most of the forecast models indicate that this break will close up as Helene races off to the northeast over the next few days. The Bermuda High will then re-establish itself and a high pressure ridge will build in, forcing 96L more to the west-northwest. A long range threat to Bermuda is possible late next week. I think it is likely that a trough of low pressure will recurve 96L northwards and out to sea before it reaches Bermuda, though. The storm is not a threat to the Caribbean or U.S. Two models--the GFDL and Canadian--forecast that 96L will eventually become a hurricane. The storm is over warm waters, and under just 10 knots of wind shear.


Figure 1. Preliminary model tracks for Invest 96L.

Hurricane Helene headed out to sea
Hurricane Helene is headed northeast out to sea. Helene is expected gradually weaken and morph into a powerful extratropical storm with hurricane force winds later today. Swells from Helene and high winds are combining to produce seas up to 12 feet high off of Cape Cod today.

I'll have an update Sunday morning.
Jeff Masters

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Gordon is trouble no more; Helene and 96L still out there

By: JeffMasters, 1:54 PM GMT en Septiembre 22, 2006

The winds and rain of former Hurricane Gordon have subsided over Ireland today, and golf's famed Ryder Cup is proceeding without weather disruptions. High winds due to the remnants of Gordon injured three people at the Ryder Cup's K Club golf course yesterday, where the final practice round was being held. A tree on the main avenue of The K Club was blown over, injuring a woman, and two men were injured when a temporary wall blew down at a bus terminal that ferried fans to distant parking lots. Radar imagery from the Irish Meteorological Service shows just a few scattered showers lingering over Ireland today. The counterclockwise circulation around the remains of Gordon helped pump hot air from Spain northward into the eastern British Islands. A record high temperature for September 21 was set with 28.4C (83.1F) in Bedford yesterday.


Figure 1. Hurricane Gordon on its way toward Ireland to play havoc with practice rounds of golf's famed Ryder Cup. Photo taken at 18:15 GMT, Sept. 17, 2006, from the Space Shuttle Atlantis. Image credit: NASA.

Gordon lashes Spain and Portugal
The remains of Gordon brought hurricane force wind gusts and heavy rain to Spain and Portugal yesterday. In the Spanish province of Galicia, four people were injured and one hundred thousand homes lost power. In Portugal, local media described chaotic scenes due to flooding from heavy rain and winds that damaged roofs and uprooted trees. Traffic was severely affected. Meteored, a Spanish weather forum, reported some impressive winds gusts:

Castro Vicaludo-Oia (Pontevedra): 168 km/h (104 mph)
Fisterra (A. Corua): 165 km/h (103 mph) (INM)
Cabo Viln (A. Corura): 152 km/h (94 mph) (INM)
Ferrol (A. Corua): 119 km/h (74 mph) (INM)
Alvedro (A. Corua): 111km/h (69 mph)
Ancares (Lugo): 101 km/h (63 mph)
Oiz (Bizkaia): 109 km/h (68 mph)

INM is the Spanish government's weather service. I thank Luiz Fernando Nachtigall, Chief Meteorologist for Brazil's MetSul Meteorologia Weather Center, for providing this information. His site's weather blog has an impressive Youtube video of the damage in Spain.

Invest 96L
Shower activity has increased today in association with a tropical wave featuring a broad surface circulation near 13N 39W, about 950 miles west-southwest of the Cape Verde Islands. This wave was designated as "Invest 96L" by the Hurricane Center Wednesday. The storm is under 10 knots of vertical wind shear and is over warm ocean waters of about 28C, and some slow development is possible over the next few days as it moves northwest over the open Atlantic. Both the GFS and GFDL predict that 96L will follow a break left by Hurricane Helene in the Bermuda High and recurve harmlessly out to sea early next week. The other models think that the break in the Bermuda High will close up and a high pressure ridge will build in, forcing 96L more to the west-northwest. In this latter scenario, a long range threat to Bermuda is possible, or perhaps even the northern Lesser Antilles Islands. None of the computer models intensify 96L into a hurricane, though.


Figure 1. Preliminary model tracks for Invest 96L.

Naming scheme for "Invest" storms
The tropical wave naming scheme goes like this: If the National Hurricane Center deems a tropical disturbance worthy of running their forecast track models on, the disturbance is given a number 90-99. A letter is affixed to the end denoting the ocean basin--"L" for the Atlantic or "E" for the Eastern Pacific. "A" is not used for the Atlantic, since that letter is reserved for cyclones in the Arabian Sea. The Navy uses the same naming scheme on their web site with zoomed-in satellite imagery of all the official "Invest" disturbances and all the regular named tropical cyclones:

http://www.nrlmry.navy.mil/tc_pages/tc_home.html

Click on "96L.INVEST" at upper left to see a full suite of conventional and microwave satellite imagery of the 96L invest area.

When NHC issues track forecasts for an "Invest", wunderground.com plots up the forecasts, and I make them available on my blog. These plots will always be labeled "Tropical Disturbance Invest". We need to fix the labels on these plots to say "96L" and make them available on the main tropical web page along with the latest satellite image of the disturbance. These improvements are on our to-do list.

Hurricane Helene headed out to sea
Hurricane Helene is headed northeast out to sea. Helene is expected to gradually weaken and morph into a powerful extratropical storm with hurricane force winds over the next few days, and pass between Iceland and the British Islands early next week. Helene's winds have blown long enough and strong enough over a vast area of ocean to cause large swells up to six feet high that have arrived along the East Coast of the U.S., prompting the issuance of rip current advisories from Florida to Cape Cod. Bermuda is also seeing some impressive waves along its shores.

I'll have an update Saturday morning.
Jeff Masters

Updated: 2:35 PM GMT en Septiembre 22, 2006

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Gordon's remains trouble Ireland; Helene generating big waves; 96L no threat

By: JeffMasters, 2:18 PM GMT en Septiembre 21, 2006

A strong tropical wave with a well-defined surface circulation is near 12N 34W, about 700 miles west-southwest of the Cape Verde Islands. This wave was officially designated as "Invest 96L" by the Hurricane Center yesterday. The storm is under about 10 knots of vertical wind shear and is over warm ocean waters of about 28C, so some slow development is possible over the next few days as it moves northwest over the open Atlantic. Shower activity has decreased with the system this morning, though, and the models are less enthusiastic about developing it than they were yesterday. This morning's QuikSCAT pass shows winds of just 15-20 mph surrounding the low. The long range GFS model predicts that this system will turn north and recurve out to sea in the middle of the Atlantic Ocean. It is pretty unlikely 96L will ever be a threat to any land areas. The next wave that emerges off the coast of Africa this weekend has a better chance of making it across the Atlantic to threaten the Lesser Antilles Islands, though, according to the latest runs of the GFS model.


Figure 1. Preliminary model tracks for Invest 96L.

Hurricane Helene headed out to sea
Hurricane Helene has begun her expected turn towards the north, and is on track to recurve harmlessly out to sea. Helene has weakened more, thanks to wind shear from a trough to her west. However, Helene's winds have blown long enough and strong enough over a vast area of ocean to cause large swells that have arrived along the East Coast of the U.S., prompting the issuance of rip current advisories from Florida to Maryland. Bermuda is also seeing some impressive huge waves today along its shores. The animation of the wave forecast from the Global Wave Model shows that these waves should die down beginning Sunday.

Gordon is gone, but don't tell the golfers that!
Hurricane Gordon degenerated to potent extratropical low yesterday, bringing heavy rain and high winds to Spain. The remnants of Gordon are headed to Ireland today, where the storm's wind and rains will play havoc with practice rounds for golf's famed Ryder Cup tournament. The tournament begins Friday. Radar imagery from the Irish Meteorological Service shows plenty of heavy rain over the island, and storm warnings for sustained winds of 50 mph, gusting to 75 mph have been issued for the waters off the west coast of Ireland. However, the tournament is being played in Straffan on the eastern end of the island, where the weather should be considerably better. Winds at Dublin Airport near Straffan were 26 mph at 9:30am local time this morning. The golf course where the tournament is to be played was closed this morning, due to wind gusts of 40 mph. Several trees were blown down on the course by the winds.


Figure 2. Hurricane Gordon as a Category 1 hurricane at 18:15 GMT, Sept. 17, 2006, as seen from the Space Shuttle Atlantis. Image credit: NASA.

Second warmest summer on record for the U.S.
Temperatures in August in the U.S. cooled down a bit compared to July, but were still well above average. According to the National Climatic Data Center, August 2006 ranked as the 11th warmest August on record. The record warmest August was 1983. The summer of 2006 (June, July, and August) ranks as the second warmest summer ever recorded. Only the summer of 1936 was hotter, by just 0.2F. The summer heat wave this year killed more than 200 people, 160 of them in California. For the period January through August, 2006 beats out 1934 as the warmest year on record in the U.S. by a huge margin, nearly 3F. With weak El Nino conditions expected to keep temperatures warmer than average across the northern 2/3 of the country this winter, it appears likely that 2006 will be the warmest year on record in the U.S.

Nationally, precipitation was above-normal for August, ranking as the 17th wettest August in the 112-year record (1895-2006). This year's January-August precipitation ranks it as the 26th driest period in the 112-year record.

Third warmest summer on record globally
June-August marked the third warmest summer globally, according to the National Climatic Data Center. The summer of 1998 was the warmest on record, 0.64C (1.15F) warmer than 2006. For the year to date, January-August, 2006 ranks as the 6th warmest such period globally.

Arctic sea ice recovers a bit
June and July saw the record lowest amount of Arctic sea ice ever recorded for those months, due to unusually warm conditions near the North Pole. However, temperatures near the pole were 1 to 2C cooler than average in August, which slowed down the melting rate. Arctic sea ice extent for August was slightly higher than the record low August coverage measured in 2005.

Tonight: the Barometer Bob Show
I'll be a guest once more tonight on the Barometer Bob Show. Bob will be interviewing me about my flight into Hurricane Hugo with the Hurricane Hunters 17 years ago. I'm lucky to be alive to tell the story!

Jeff Masters

Updated: 2:20 PM GMT en Septiembre 21, 2006

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Gordon hits the Azores; new Invest 96L; Helene heads out to sea

By: JeffMasters, 2:15 PM GMT en Septiembre 20, 2006

A strong tropical wave with plenty of heavy thunderstorm activity and some low-level spin has developed near 9N 29W, about 450 miles southwest of the Cape Verde Islands off the coast of Africa. This wave has been officially designated as "Invest 96L" by the Hurricane Center this morning. The storm is under about 10 knots of vertical wind shear and is over warm ocean waters of about 28C, so some slow development is possible over the next few days as it moves west-northwest over the open Atlantic. Most of the models predict slow development will occur, but none develop it into a hurricane. The long range GFS model predicts that this system will pass north of the Lesser Antilles Islands and possibly threaten Bermuda before recurving out to sea.


Figure 1. Preliminary model tracks for Invest 96L.

Hurricane Helene headed out to sea
Hurricane Helene has begun her expected turn towards the northwest, and is on track to recurve harmlessly out to sea. Helene has weakened some since yesterday--wind shear from the trough to her west has eroded the cloud pattern on that side, and the storm now has a distinctly lopsided appearance on satellite imagery. Helen is still over relatively warm water and under light wind shear, so may be able to reintensify into a Category 3 hurricane later today or tomorrow.


Figure 2. This morning's line-up of storms. Image credit: Naval Research Laboratory, Monterey.

Gordon pounds the Azores
Hurricane Gordon whipped through the Azores islands this morning as a Category 1 hurricane, but preliminary reports indicate no deaths or injuries occurred, and little damage was reported. Animations of satellite microwave imagery from CIMSS show that the center of Gordon passed over the southeastern-most island of Santa Maria, where power outages and fallen trees blocking roads created some minor problems. Winds on Santa Maria Island at 8am local time peaked at 56 mph, gusting to 82 mph. Gordon is rapidly weakening over cold waters, and is expected to become a powerful extratropical storm this afternoon. Gordon may cause trouble for golf's Ryder Cup in Ireland, due to begin Friday. Gordon is expected to move over or just offshore Ireland as a powerful extratropical storm on Friday and stall there, bringing high winds and intermittent heavy rain to Ireland for several days.

Hurricane history of the Azores
The Portuguese-owned Azores Islands, located about 1,500 km (930 miles) off the western coast of Europe, does not have a long and storied hurricane history. The ocean waters surrounding the islands are typically 22-23 C during hurricane season, which is 4-5 C below what is needed to sustain a hurricane. Occasionally, a fast-moving hurricane caught in the jet stream can make it all the way to the islands before decaying to a tropical storm; Gordon is the ninth hurricane since 1900 that managed to affect the Azores. All of these were Category 1 storms except for a Category 2 storm in 1926. I could find no mention anywhere of any deaths or damage having occurred as the result of these hurricanes.

The last time a hurricane hit the Azores was in 1998, when the not-so-terrible version of Hurricane Ivan passed through as a Category 1 storm. Ivan missed hitting any populated islands directly, and did little damage. Hurricane Emmy passed through the Azores in 1976 as a Category 1 storm. Emmy also did little damage, but tragically, a Venezuelan Air Force airplane carrying a school choir to Europe tried to land in the Azores at the height of the hurricane and crashed, killing all 68 people on board. The other major hurricane related tragedy to affect the islands occurred on On September 21, 1957, when the German sailing ship Pamir, with 86 crewmen aboard, was caught in Category 1 Hurricane Carrie. The ship sank, and only six survivors were found after a massive rescue effort. The shipwreck received enormous international media attention as a result and was perceived as a worldwide tragedy.

My next update will be Friday morning.
Jeff Masters

Updated: 2:31 PM GMT en Septiembre 20, 2006

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Azores Islands brace for Gordon; Helene not a threat

By: JeffMasters, 2:12 PM GMT en Septiembre 19, 2006

The Azores Islands are bracing for the arrival of Hurricane Gordon, which is expected to rip through the islands tonight as a Category 1 hurricane with 75 mph winds. Gordon is under about 20 knots of shear, and will be moving over cool waters of 22-23 C this afternoon, so a decrease in intensity from its current 85 mph winds is likely before the storm moves through the Azores. Hurricane force winds extend out 40 miles from the center, and the islands of the Azores are widely scattered enough that Gordon may not bring hurricane force winds to any of the islands. The first place to feel Gordon's effects will be the northwesternmost islands of Corvo and Flores. The link for today's weather conditions on Flores can be found here. About 4,000 people live on these two islands, about 2% of the total population of the Azores. Gordon now appears to be moving slightly south of due east, which may mean the more southern islands will feel the worst of Gordon.

Gordon's rapid forward speed near 30 mph may allow the storm to make it all the way to Spain or Portugal on Wednesday night as a tropical storm, making it only the second tropical cyclone ever to hit the Iberian Peninsula (Tropical Depression Vince of 2005 was the first). It it more likely, though, that Gordon will arrive as a powerful extratropical storm with 50 mph winds.

Hurricane Helene
Hurricane Helene remains a powerful Category 3 hurricane, but we are now confident that this storm presents no threat to land. Beginning with yesterday morning's computer model runs, all of the reliable models have been consistently been predicting that the next trough of low pressure moving over the Atlantic will be strong enough to turn Helene northwards, then recurve her out to sea. My confidence in this forecast is high, because the NOAA P-3 and Gulfstream IV jet have been probing Helene for the past two days as part of a research mission into how dry Saharan air affects hurricane intensification (the SALEX project). The computer models have had the advantage of having this high-quality data available for their runs. Given this factor, plus the high degree of unanimity of the models in turning Helene northeast over multiple runs, we can be confident that Helene poses no threat to the U.S., Bermuda, or Canada.


Figure 1. Current satellite image of Helene, updated every 1/2 hour.

Helene is over warm waters of about 28C, and under about 5-10 knots of wind shear. These conditions favor intensification for another two days, and Helene could be the first Category 4 hurricane in the Atlantic this year.

The rest of the tropical Atlantic
A non-tropical area of low pressure a few hundred miles east of Cape Hatteras, North Carolina, has a slight chance of development as it drifts slowly east. Most of the computer models are forecasting that a tropical storm will develop later this week in the region between Africa and the Lesser Antilles Islands.

I'll have an update Wednesday morning.
Jeff Masters

Updated: 9:38 PM GMT en Septiembre 19, 2006

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Helene a major hurricane

By: JeffMasters, 2:07 PM GMT en Septiembre 18, 2006

Hurricane Helene continues to intensify, and is now the season's second major hurricane. Helene is over warm waters of about 28C, and under about 10-15 knots of wind shear. These conditions favor intensification for another two days, and Helene could be the first Category 4 hurricane in the Atlantic this year. Helene is currently headed more north than west, following a cut little brother Gordon has made through the Bermuda High. However, this cut is expected to close up later today, and the Bermuda High will re-establish itself and force Helene more to the west. By Wednesday or Thursday, a strong trough of low pressure will be moving off the East Coast and should turn Helene more to the north. It remains to be seen if this trough will be strong enough to finish the job and fully recurve Helene. If not, the Bermuda High will build back in, forcing Helene more to the west again, and potentially allowing it to strike the Mid-Atlantic or New England coasts of the U.S., or the Maritime Provinces of Canada. The models are VERY fuzzy at these long time scales, but the odds are that Helene would have yet another trough of low pressure to contend with before she could strike the coast. The computer models in general have performed poorly with the long-range track of Helene, and I am putting more stock in the historical record of what similar hurricanes have done in the past. I modified historical map of hurricanes to include all Category 1-5 hurricanes passing within 300 miles of Helene's current position. This map offers us some reassurance that Helene will probably not make landfall in the U.S. or Canada--only one of the 16 storms plotted have done so, and this storm <>a href=http://www.wunderground.com/hurricane/at200309.asp(Isabel, 2003) started further south than Helene's current position. I still put Helene's chances of a U.S. landfall at about 10%. Bermuda is at considerably higher risk, but the storm is still too far away to have a very good idea of this risk. Bermuda is a small target, and the five day track forecast errors are on the order of 350 miles.


Figure 1. Current satellite image of Helene, updated every 1/2 hour.

Mexico cleans up from Hurricane Lane
Mexico is cleaning up the damage from Hurricane Lane, which made landfall at 12:15pm PDT Saturday as a powerful Category 3 hurricane with 125 mph winds. However, Lane struck a sparsely populated region of the Mexican coast about 50 miles northwest of Mazatlan, and damage was mostly limited to washed out roads, toppled power lines, and at least one destroyed bridge. The storm surge of approximately six feet affected only an uninhabited barrier island and some adjacent farmland, and did very little damage. The extreme Category 3 winds of the eyewall affected an area of coast about 20 miles wide and stretching 20 miles inland. Only a few hundred people lived in this region.

The rest of the tropical Atlantic
Hurricane Gordon is still out there, but is no threat to land. A non-tropical area of low pressure a few hundred miles east of Cape Hatteras, North Carolina, has a slight chance of development as it drifts slowly east. Shower activity has decreased in this system this morning. Some of the computer models are forecasting that a tropical wave moving off the coast of Africa today will develop into a tropical storm later this week.

Typhoon Shanshan
In the Western Pacific, Typhoon Shanshan made landfall Sunday in southwestern Japan as a Category 1 storm. Shanshan killed nine and injured over 280 in Japan. Its powerful winds were able to lift a train off its tracks and lay it on its side. The typhoon brought the ninth strongest winds to the Korean peninsula in history, according to the Korea Meteorological Administration. Wind gusts reached 164 km/hr (102 mph) on Korea's Ullung Island as it passed by. Shanshan, the Chinese-language name for a young girl, was the 13th typhoon of the Western Pacific season.

Remainder of hurricane season outlook
I posted my outlook for the remainder of hurricane season Friday, in case you missed it.

I'll have an update Tuesday morning.
Jeff Masters

Updated: 3:16 PM GMT en Septiembre 18, 2006

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Lane spares Mexico the worst; Helene strengthens

By: JeffMasters, 2:05 PM GMT en Septiembre 17, 2006

Hurricane Lane made landfall at 12:15pm PDT Saturday as a destructive Category 3 hurricane with 125 mph winds. Lane struck a sparsely populated region of the Mexican coast about 50 miles northwest of Mazatlan. The storm surge of approximately six feet affected only an uninhabited barrier island and some adjacent farmland, and did very little damage. The extreme Category 3 winds of the eyewall affected an area of coast about 20 miles wide and stretching 20 miles inland. Only a few hundred people lived in this region, and wind damage from Lane was mostly felt in the city of Culiacan about 30 miles inland. Lane had weakened to a Category 1 hurricane when it passed 30 miles east of that city of 750,000, and brought sustained winds of approximately 65 mph to the city.

Lane has been downgraded to a tropical storm, and is rapidly breaking up over the high mountains of Mainland Mexico. Flooding remains a concern today, and Lane could trigger flash floods in the mountains thanks to its expected 5-10 inches of rain. Lane has been responsible for two deaths so far--a man killed in the village of Pueblos Unidos when he was knocked over by fierce winds, and a 7-year-old boy in a rockfall in Acapulco. Overall, Mexico was very lucky with Lane. Had the storm made a direct hit on Mazatlan, it would have been one of the most destructive Pacific hurricanes of all time for Mexico, and Lane would have become just the 4th Pacific Mexican hurricane to have its name retired.


Figure 1. Hurricane Lane at landfall. Image credit: Servicio Meteorologico Nacional of Mexico.

Helene strengthens
Hurricane Helene is now a large and impressive hurricane, with a huge 50 mile diameter eye. Helene continues to strengthen, but it appears that the storm will be no threat to land, with the possible exception of Bermuda. The computer models are in two camps this morning--the GFS and BAMM models, which take the storm on a westerly track starting Monday, and the rest of the models, which show recurvature to the north. The models differ in how they handle a weak trough of low pressure that is expected to pass to the north of Helene early this week. If the GFS and BAMM are right, the trough will be too weak to pick up Helene, and high pressure will build in, forcing the storm to the west for several more days. The rest of the models think that the trough will be deep enough to turn Helene to the north. These model solutions are more likely to be correct the stronger and larger Helene grows, since a larger storm will extend further north and higher in the atmosphere, making it more likely to feel the effects of the trough of low pressure.

If this trough does miss picking up Helene, the storm has to avoid being pulled north by one or two more troughs in order to make it all the way to the U.S. East Coast. This is a pretty tall order this time of year, as the troughs coming off the East Coast are expected to get stronger and dive further south. The GFS model is predicting a trough late this week will turn Helene northwards, bringing the hurricane very close to Bermuda on Sunday or Monday of next week.

The rest of the tropical Atlantic
Hurricane Gordon is still out there, but is no threat to land. There are no other threat areas to discuss.

Remainder of hurricane season outlook
I posted my outlook for the remainder of hurricane season Friday, in case you missed it.

I'll have an update Monday morning.
Jeff Masters

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Very dangerous Hurricane Lane heads for landfall

By: JeffMasters, 3:50 PM GMT en Septiembre 16, 2006

Hurricane Lane has intensified into a small but very dangerous Category 3 hurricane, and is now bearing down on the Pacific Mexican coast north of the resort town of Mazatlan. The historical map of Eastern Pacific hurricanes shows that Lane is the strongest September hurricane ever to affect this region of the Pacific coast of Mainland Mexico. Lane passed about 45 miles to the west of Matazlan this morning at 5am PDT. Hurricane force winds extend out only 30 miles from the center of Lane, and Mazatlan airport has recorded top winds of only 25 mph so far today. Lane is responsible for one death. Lanes' heavy rains triggered a landslide yesterday that killed a 7-year-old boy in Acapulco. Lane brushed the Mexican coast between Acapulco and Puerto Vallarta Friday, bringing heavy rains of 4-8 inches, then made a direct hit on a group of islands called the Islas Tres Marias as a Category 2 hurricane. There is no word yet on how the islands fared. The islands are home to a large penal colony.


Figure 1. Latest satellite image of Lane, updated every half hour.

Cabo San Lucas radar shows that Lane has developed concentric eyewalls, and is probably near peak intensity. The main threat from Lane is his winds. Lane has a small eye about ten miles in diameter, and a small region of the Mexican coast about 20 miles wide will be subject to the extreme winds of the eyewall. These 125 mph winds will cause tremendous damage. Hopefully, Lane will miss the populated towns of El Dorado and La Cruz and come ashore on a relatively sparsely populated section of coast. The other major threat is rainfall. Ten inches of rain will be common in the mountainous region of Mexico Lane is expected to cross, triggering flash floods. Storm surge flooding should be less of a problem, since the ocean waters are deep offshore, which will allow only a six-foot storm surge to build.

Lane is the sixth major hurricane in the Eastern Pacific this year. It is often the case that a quiet year in the Atlantic is offset by an active year in the Eastern Pacific, and vice versa. That has certainly been the case the past two years. The Atlantic has seen only one major hurricane this year. Last year the Atlantic had seven major hurricanes, and the Eastern Pacific just one. The difference in activity between the two ocean basins is not fully understood, but has been commonly linked to the El Nino phenomena.

The mountains of central Mexico should dissipate Lane within three days, and moisture from the storm is no longer expected to reach the U.S.

Helene becomes a hurricane
Helene has intensified into a hurricane this morning, and now has a eye, well-formed low-level spiral bands, and some solid and improving upper-level outflow. Helene is over warm 27-28C waters, shear is a low 5-10 knots, and the storm should intensify into a Category 2 hurricane by Monday.

Helene may be a threat to Bermuda and/or the Maritime provinces of Canada, but the odds of a strike on the U.S. are less than 10%. History shows that the large majority of hurricanes that traverse this part of the Atlantic end up recurving. One very notable exception is the famed New England Hurricane of 1938, which followed a very similar path to Helene's current track. Two strong troughs of low pressure are expected to push off the East Coast over the next week. If the first trough does not pull Helene northwards far enough to recurve her out to sea, the second one should almost certainly finish the job--before Helene can make it all the way to the U.S. It is too early to tell what the risk might be to Bermuda; the exact strength of the first trough 4-5 days from now is uncertain, and will determine how far west Helene is able to penetrate. The latest run of the GFS model puts Helene very near Bermuda on Sunday September 24.

Gordon on the decline
Hurricane Gordon is barely a hurricane, thanks to some strong shear and dry air. Margie Kieper did a nice job in her View from the Surface blog documenting Gordon's demise. Gordon is headed northward out to sea, and is not a threat to land.

The rest of the tropical Atlantic
A strong tropical wave with plenty of spin but only a little thunderstorm activity is just off the coast of Africa near the Cape Verde Islands, and is headed northwest out to sea. This system may show some slow development over the next few days.

Remainder of hurricane season outlook
I posted my outlook for the remainder of hurricane season yesterday, in case you missed it.

I'll have an update Sunday morning.
Jeff Masters

Updated: 4:14 PM GMT en Septiembre 16, 2006

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Outlook for the remainder of hurricane season

By: JeffMasters, 8:15 PM GMT en Septiembre 15, 2006

Could Ernesto end up being the worst the hurricane season of 2006 has to dish out? With the season more than half over, and no landfalling storms in sight, this year in no way resembles the Hurricane Season of 2005, when we had 15 named storms, 8 hurricanes, and 4 major hurricanes by this date. Our tally so far this year is a relatively meager 8 named storms, 2 hurricanes, and 1 major hurricane, right near average. Looking at the plot of typical hurricane activity for the Atlantic (Figure 1), we see that we are almost a week past the peak of hurricane season, which was September 10. We still have a long road ahead--hurricane activity stays high for another four to five weeks, on average. Let's analyze analyze what the remainder of hurricane season may have in store for us.


Figure 1. Ernesto--the main event of the hurricane season of 2006? Image credit: NOAA Visualization Lab.


Figure 2. Climatological Atlantic hurricane and tropical storm activity.

Sea Surface Temperatures (SSTs)
It's mid-September, and SSTs have peaked in the Atlantic and are on a slow decline. Still, water temperatures will remain warm enough to support hurricanes throughout usual Atlantic development areas through the end of October. SSTs are 0.5-1.5C warmer than normal right now (Figure 3), which is a huge amount of extra heat energy. The Bermuda High has stayed relatively weak all of August and September, leading to lighter trade winds that have kept the ocean warm due to reduced evaporative cooling.


Figure 3. Difference of SSTs from normal for Sep 11, 2006.

Wind shear and El Nio
An El Nio is on the way, according to the latest El Nio discussion posted September 7 by NOAA's Climate Prediction Center. A steady warming of the waters in the Equatorial Pacific near the coast of South America, combined with stronger than usual westerly winds over the Equatorial Pacific, point toward the emergence of a weak El Nio episode beginning in October or November. As most of you know, El Nio conditions put a major damper on both the number and intensity of Atlantic tropical cyclones. This is primarily due to increased wind shear. The upper air winds that develop when one heats the Equatorial Eastern Pacific waters tend to blow from west to east over the Atlantic at high speed. Since the tropical Atlantic trade winds near the surface typically blow the opposite direction, this creates a lot of shear that makes it difficult for a tropical cyclone to survive. Since the peak portion of hurricane season began in late August, wind shear over the tropical Atlantic, western Caribbean, eastern Caribbean, and Gulf of Mexico has been near or below normal, so there is no sign that a developing El Nio is suppressing hurricane activity yet. When I eyeball the shear forecast for the coming two weeks from the GFS model, I don't see any sign that an El Nio-induced increase in shear is in the offing this September.

While the lack of wind shear would seem to favor an active hurricane season, what wind shear we have had has been of exceptionally high quality. The jet stream has spun off a continual series of upper level "cold lows" over the Bahamas and central Caribbean that have brought hostile wind shear to any tropical waves or tropical storms that have tried to approach. This jet stream pattern has been in place since early June, and shows no signs of changing through the end of September.

Dry air and vertical instability
Hurricanes like plenty of moist, unstable air. This has been lacking this year, thanks to an above-average amount of dry Saharan air coming off the coast of Africa. For example, take a look at the instability plot for the eastern Caribbean, where many of last year's fiercest storms formed. Instability has been well below normal this year. Model projections through the rest of September show no change to the basic atmospheric pattern over the Atlantic, and I expect lack of instability will continue to inhibit hurricane development.

Steering pattern
The large scale jet stream pattern and associated positioning of the Bermuda High has remained unchanged since early June, and is forecast to remain the same through the end of September. This pattern puts a trough of low pressure over the U.S. East Coast, which will act to recurve storms approaching the U.S. or Caribbean. Now that we are entering late September, the troughs are getting stronger and extending farther south, making recurvature even more likely. The current pattern has been for tropical waves that form into tropical storms to emerge from Africa at about the latitude of the Cape Verde Islands (12-15 north latitude). This is far enough north to make recurvature very likely. This pattern is forecast to continue through the end of September, and I don't expect any of these African systems will be able to avoid recurvature. We will probably get two or three more of these recurving storms before the usual end to the African tropical storm season in early October.

Summary
Given that the current jet stream pattern that favors recurving storms and shear-producing upper level lows over the Bahamas and central Caribbean is forecast to continue until the end of September, plus Bill Gray's September 1 forecast of only two named storms and one non-major hurricane in October, I don't believe any major hurricanes will affect the U.S. or Caribbean the remainder of hurricane season. I expect one or two tropical storms or Category 1 hurricanes will form in October from the remains of old cold fronts that push off the coast of the U.S. A hurricane of this nature is most likely to affect the west coast of Florida or the Outer Banks of North Carolina, and rarely has enough time over water to make it to Category 3 status. In total, I expect 5 more named storms, 3 hurricanes, and 1 major hurricane this season.

Additional thoughts
I answered a series of questions on what the rest of this year's hurricane season might be like for Texas, the Katrina disaster, and the global warming/hurricane connection for houstonist.com that appeared in today's edition.

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Helene slowly intensifying; Lane threatens Mexico

By: JeffMasters, 1:53 PM GMT en Septiembre 15, 2006

Tropical Storm Helene continues to be a very large and disorganized system. However, visible satellite imagery from this morning is now showing a slow improvement in the organization of the low-level spiral bands, and the amount and intensity of the thunderstorm activity near Helene's core is increasing. Given that the storm is over warm 27-28C waters and the shear is a low 5-10 knots, I expect Helene will slowly intensify into a hurricane by Sunday. The dry air to Helene's north and west is farther away and more dilute, so should not inhibit intensification significantly.

The computer track models still have a wide spread in the long-range track for Helene, but all of them take the storm north of the Lesser Antilles. Helene may be a threat to Bermuda and the U.S. East Coast late next week, but the odds of a strike on the U.S. are less than 10%. History shows that the large majority of tropical storms that form in this part of the Atlantic end up recurving. A very strong trough of low pressure is expected to push off the East Coast by Wednesday, and this trough should be able to pull Helene northwards and recurve the storm harmlessly out to sea.


Figure 1. Latest satellite image of Helene, updated every half hour.

Gordon on the decline
Hurricane Gordon, the first major hurricane of the season, is a major hurricane no longer. Strong upper-level winds from the west have eroded the northwest side of the storm, and the once prominent eye is now gone. About 20 knots of wind shear is now affecting the storm, and this shear is expected to increase and the waters underneath it cool over the next few days. Gordon is headed northward out to sea, and is not a threat to land.

Tropical Storm Lane nears hurricane strength
Tropical Storm Lane continues to intensify just off the Mexican Pacific Ocean coast near Puerto Vallarta. Animations of microwave satellite images show that Lane is moving parallel to the coast, about 60 miles offshore, remarkably close to the track of Hurricane John earlier this month. Lane is over warm waters and under light shear, and and has the potential to become a hurricane later today. The only inhibiting factor for intensification might be the storm's close proximity to land. Lane will be drawing in dry continental air from mainland Mexico that might slow down the intensification process. Hurricane John was able to intensify into a Category 4 hurricane under virtually the same conditions, but Lane is a much smaller storm, and might be more seriously impacted by interaction with land. If Lane can avoid passing too close to land areas, she may have enough time to intensify into a Category 2 hurricane before landfall. The people of Baja, who are still cleaning up the damage and repairing the roads washed out by Hurricane John, are probably not too happy to see Lane approaching on Cabo San Lucas radar.

Moisture from Lane could potentially reach southern Arizona and New Mexico by Wednesday and cause flooding concerns there.

The rest of the tropical Atlantic
Shower activity has increased over the extreme southwest Caribbean off the coast of Panama. However, the area affected is small and likely to move ashore over Nicaragua before any development can occur. A strong tropical wave with plenty of spin and heavy thunderstorm activity has emerged from the coast of Africa this morning. This wave is over warm waters, and wind shear is a modest 10-20 knots. This wave has the potential for some slow development over the next few days as it moves over or just south of the Cape Verde Islands. Tropical waves that emerge this far north usually end up recurving out to sea.

Remainder of hurricane season outlook
I'll post my outlook for the remainder of hurricane season this afternoon by 4pm EDT.

Jeff Masters

Updated: 1:55 PM GMT en Septiembre 15, 2006

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Helene, Gordon, Lane, Florence, and a fire tornado

By: JeffMasters, 1:50 PM GMT en Septiembre 14, 2006

It's a typically active mid-September day in the Atlantic, with the first major hurricane of the year, Gordon, spinning out to sea, and a new tropical storm to watch, Helene. Neither of these storms are likely to affect land, and the long range 2-week GFS model forecast offers no hint of any future threats coming in the Atlantic. With hurricane season now more than half over, the seemingly radical notion that the worst storm of the season will end up being Ernesto is not so far-fetched. Still, there is another full month of peak hurricane season to go, and we still need to keep an eye on Helene, which could cause trouble.

Florence
The remains of Hurricane Florence gave Newfoundland a pounding yesterday, bringing hurricane force winds and 30-foot seas to the coast. One house was reported destroyed on an island off the coast, and there were scattered reports of power outages and flooding. The remains of Florence will continue across the Atlantic, and likely bring heavy rain and 40 mph wind gusts to Ireland on Sunday.

Gordon headed out to sea
Hurricane Gordon intensified into the first major hurricane of the season last night, but appears to be starting a slow decline in strength. Strong upper-level winds from the west are creating about 15 knots of wind shear over the storm, and helping stretch it into an east-west oriented oval shape. Wind shear over Gordon is expected to increase and the waters underneath it cool over the next few days. Gordon is headed northward out to sea, and is not a threat to land.


Figure 1. Latest satellite image of Gordon, updated every half hour.

Helene
Tropical Depression Eight got its act together enough last night to barely qualify as the eighth named storm of the season, Helene. Helene is very disorganized and has a large sloppy circulation center. A QuikSCAT satellite pass from this morning shows this broad center nicely, and reveals only a few patches of winds over 40 mph. As we saw with Florence, it can take many days for a weak tropical storm with a large circulation center to organize into a hurricane. Still, the waters under Helene are a warm 27-28C, the shear is a low 5-10 knots, and these favorable conditions for intensification are expected to persist for several days. Helene should be able to intensify into a hurricane by 3-4 days from now, and possibly into a major hurricane thereafter. Some dry air to its north and west may interfere with this intensification.

The computer track models have a wide spread in the track for Helene, but all of them take the storm north of the Lesser Antilles. While a long-range threat to Bermuda and the U.S. East Coast is still a possibility, the odds of this happening are low. History shows that the large majority of tropical storms that form in this part of the Atlantic end up recurving harmlessly out to sea. With the active jet stream pattern we've seen since early June expected to continue for at least the next two weeks, I expect that Helene will end up recurving out to sea east of Bermuda.

More trouble for Mexico
Tropical Storm Lane formed off the Pacific coast of Mexico yesterday, and this storm has the potential to be the most trouble of any storm discussed so far. Lane is expected to track parallel to the coast and threaten Baja, similar to what Hurricane John did earlier this month. Lane is over warm waters and under light shear, and and has the potential to become a hurricane by Friday. Lane probably does not have time to intensify into a major hurricane, but a Category 2 hurricane would not be a surprise.

The entire coast of Mexico affected by John is also at risk from Lane. The storm could move ashore on the mainland Mexico coast south of Puerto Vallarta, like the GFDL model is forecasting. The GFDL had the best performance of any of the computer models for John, so residents along the mainland Mexican coast should prepare for a possible direct hit by a Category 1 hurricane on Friday.

Moisture from Lane could potentially reach southern California and Arizona by Wednesday and cause flooding concerns there.

The rest of the tropical Atlantic
Thunderstorm activity is increasing today along a cold front stretching from Cape Hatteras, NC, to the waters east of Florida. This area will have to be watched the next two days for development. Shower activity associated with a tropical wave passing through Puerto Rico and the surrounding region have diminished, and development is unlikely here.

Fire tornado
Finally, I had to link this photo of a fire tornado taken by wunderphotographer Photo5150. Some fires are able to create such a strong updraft with their extreme heat that the air rushing in at the surface to replace the air lifted creates a fire tornado. This is definitely the most awesome photo of a fire tornado I've ever seen!

Jeff Masters

Updated: 1:50 PM GMT en Septiembre 14, 2006

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Tropical Depression Eight: the one to watch

By: JeffMasters, 2:12 PM GMT en Septiembre 13, 2006

Hurricane Florence is now a powerful extratropical storm passing along the south coast of Newfoundland. The storm still has winds of hurricane force, as evidenced by the sustained winds of 76 mph gusting to 93 mph reported at Newfoundland's Segona Island this afternoon. The QuikSCAT imagery from this morning shows an impressive storm with 55+ mph winds affecting a large swath of ocean near Canada.

Gordon is headed out to sea.
Hurricane Gordon became the third hurricane of the season last night, and is expected to remain a Category 1 hurricane for another two or three days until increasing wind shear and cooler waters weaken the storm. Gordon is headed northward out to sea, and is not a threat to land. I'm not going to talk about this storm very much.


Figure 1. Saharan Air Layer (SAL) analysis from 9Z (5am EDT) Sep 13, 2006. The bright orange layers show where very air air laden with Saharan dust lies. Note that TD 8 has to contend with some dry air from the SAL to its north and west, while Hurricane Gordon is in a moister, more favorable environment.

The one to watch: Tropical Depression Eight
The storm we really need to focus on is Tropical Depression Eight. This depression has the potential to grow into a major hurricane that may affect Bermuda or the U.S. East Coast next week. TD 8 is currently having difficulty organizing, due to the presence of dry air to its north and west (Figure 1), and about 20 knots of wind shear. TD 8 also has a very large circulation, and as we saw with Florence, it can take such storm a very long time to organize.

The computer track models all agree on a general westward motion the next five days, taking TD 8 into the middle Atlantic. It appears at this time that the storm will gain enough latitude to pass north of the Lesser Antilles Islands, since a trough of low pressure should pull the storm on a more west-northwesterly track 3-5 days from now. After that, the future track is uncertain. The long-range GFS model shows a more westerly track and an eventual threat to Bermuda late next week, and it is not out of the question that TD 8 could make it all the way to the U.S. However, the odds are against this. History shows that the large majority of tropical depressions that form in this part of the Atlantic end up recurving harmlessly out to sea. With the active jet stream pattern we've seen since early June expected to continue for at least the next two weeks, I expect TD 8 will recurve before reaching the U.S.

Research project studying TD 8
A new research tool is being used to study Tropical Depression Eight. The driftsonde is being used for the first time to aid in hurricane research. The driftsonde is a special high-altitude balloon that floats in the stratosphere at 70,000 feet and can launch special mini-dropsondes that float down on parachutes and radio back information on winds, pressure, temperature, and humidity as they fall to earth. The driftsonde will typically launch two mini-dropsondes per day, but can launch up to one per hour if special high density data is desired. The data from these mini-dropsondes (in theory) should be making it into the global computer models that forecast hurricanes, providing valuable data over data-void ocean regions that should help provide better forecasts. The tricky part is launching the driftsondes at the right time so that they drift from Africa to the Caribbean over a developing tropical cyclone. At least seven driftsondes have been launched since August 28. The research is being done as part of an international field project to help learn about the African Monsoon and hurricane formation called the African Monsoon Multidisciplinary Analysis (AMMA). Here's a sample of the status of some of the driftsonde missions, taken from the AMMA webpage. Note that the acronym AEW refers to "African Easterly Wave", meaning the tropical waves I talk so much about.

UPDATE:

MISSION #4 IS TERMINATED: Despite the tilted gondola, gondola #4 allowed the sampling of extra-tropical dry intrusions off the coast, west of Dakar and yesterday we dropped 4 sondes on the southeastern edge of tropical depression #7 (see attached document).

MISSION #5 IS AIRBORNE: Driftsonde #5 is flying over a streak of very moist air that we sample every three hours. It is now heading south and is located at about 11N and 41W.

MISSION #6 IS AIRBORNE: After sampling a weak trough of an AEW (1 sonde/3hrs), driftsonde #6 is heading to a more active area immediately off the coast where storm formation is predicted by different models (sampling strategy: 1 sonde/3hrs in the area). It should be over Dakar tomorrow and could be considered as a possible contributor to SOP-3.

MISSION #7 SHOULD BE LAUNCHED TODAY IF POSSIBLE: This driftsonde should be launched in the eastern part of a trough associated with an AEW (no possible launch the last two days due to strong wind and showers). Coordination with SOP-3 is possible with this driftsonde which should be over Dakar the day when SOP-3 begins (in 3 days).


Carolinas
Several of the computers models are forecasting that a tropical low pressure system might form off the Carolina coast on Friday, then scoot quickly northeastward out to sea. We'll have to watch the cold front expected to push off the East Coast Thursday to see if it spawns such a storm.

I'll be back with an update Thursday morning.
Jeff Masters

Updated: 4:05 PM GMT en Septiembre 13, 2006

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Florence and Gordon and TD 8

By: JeffMasters, 1:55 PM GMT en Septiembre 12, 2006

Bermuda is cleaning up after a brush with Hurricane Florence that brought only minimal damage. The eye of Florence passed 52 miles to the west of the island at 10am Monday, bringing sustained winds of 80 mph gusting to 110 mph to the eastern end of the island. Higher winds likely occurred on the island's western end. The storm surge brought only minor flooding, and Florence's winds damaged just five buildings, one of them because of a rare tornado on Sunday afternoon. No deaths or injuries were reported, except to two pink flamingos at the zoo killed by falling branches. All but 6,000 of the 25,000 customers that lost power have had their power restored by this morning.

Florence continues north towards an encounter with Newfoundland. The storm is looking very much like an extratropical storm on satellite imagery this morning. Cooler waters and hostile upper level winds are gradually weakening the storm. Florence should still pack plenty of punch as a 60 mph tropical storm Wednesday afternoon as it passes over the southeast corner of Newfoundland. The remains of Florence will continue east and may bring heavy rain and 40 mph winds to Ireland on Saturday.


Figure 1. Today's lineup of storms. Invest 94L has now become Tropical Depression 8. Image credit: Navy Research Lab.

Gordon headed out to sea
Tropical Storm Gordon formed yesterday from the area of disturbed weather that tailed Florence all the way across the Atlantic. Gordon is over warm waters and under light wind shear of 10 knots, and is expected to intensify into the season's third hurricane by Wednesday. Gordon is being pulled north by the same trough of low pressure that grabbed Florence, and the storm is a threat only to shipping interests.


Figure 2. Preliminary model tracks for Invest 94L.

Tropical Depression Eight
A strong tropical wave with impressive rotation and plenty of intense thunderstorm activity that emerged from the coast of Africa yesterday is now Tropical Depression Eight. Wind shear as analyzed by the University of Wisconsin CIMSS group is a bit high, 15 knots, but the NHC's SHIPS model puts the shear much lower, at 6 knots. The shear is expected to stay low the next three days, and this should be Tropical Storm Helene by Wednesday night. There is an large area of dry air and African dust to the west and north of the system that may slow down the long-term development of the storm, and the storm may encounter higher shear due to stronger upper level winds on Friday.

The center of circulation was located about 200 miles southeast of the Cape Verde Islands, near 14N, 22W at 4:12am EDT today, according to the QuikSCAT satellite. Winds were about 20-25 mph near the center, with some stronger squalls several hundred miles to the south of the center. While it is too early to be confident of this storm's long range track, the historical map of similar September tropical depressions forming in this region show that only about 30% of these systems strike the Lesser Antilles or U.S. East Coast. Given this fact, plus the long range forecasts of an active jet stream pattern in the Atlantic the next two weeks, I'd give TD 8 a less than 20% change of striking land.

I'll be back with an update Wednesday morning.
Jeff Masters

Updated: 3:33 PM GMT en Septiembre 12, 2006

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Florence departs; Gordon is born

By: JeffMasters, 8:04 PM GMT en Septiembre 11, 2006

Hurricane Florence has done its worst in Bermuda, and is now headed north towards Newfoundland. The Bermuda airport did briefly record sustained hurricane force winds of 74 mph near 11am local time. The maximum winds reported on their regular observations occurred at 12:55pm local time: sustained winds of 66 mph, gusting to 90 mph. The airport is at the extreme eastern end of the island, and the large eye of Florence passed just to the west of the island. Thus, the western end of the island probably experienced higher winds of 80-90 mph. Florence's winds probably caused relatively minor damage. Bermuda's infrastructure is well able to withstand winds of Category 1 force, since much of the utility lines are buried underground, and the building codes demand that structures be able to withstand 110 mph Category 2 hurricane winds. The primary damage from Florence was probably a result of the expected 6-8 foot storm surge, topped by large battering waves up to 20 feet high.

Florence is expected to gradually weaken as wind shear increases and ocean temperatures decrease, and will pass close or over Newfoundland later this week as a powerful extratropical storm with 60 mph winds.

Gordon on the way towards Bermuda
The Hurricane Hunters investigated Tropical Depression Seven this afternoon, and found winds of 47 knots at their 1500 flight level at 3pm EDT. This implies surface winds of 40-45 mph, and TD 7 will likely be upgraded to Tropical Storm Gordon at 5pm. The satellite appearance continues to improve, with the heavy thunderstorm activity moving over the center of circulation and low-level spiral bands starting to develop. Wind shear has fallen to just 10 knots, the waters are a warm 29C, and some continued development is likely today. Gordon is likely to follow a track similar to Florence, and may be a threat to Bermuda. However, most of the computer models indicate Gordon will pass well to the east of the island.

Bermuda's worry after that: a new African wave
A strong tropical wave with impressive rotation and plenty of intense thunderstorm activity has emerged from the coast of Africa today. Several of the reliable computer models are forecasting that this will develop into a tropical storm or hurricane that heads westward across the Atlantic. Wind shear is a low 10 knots, and water temperatures are warm. If this system does develop, it would likely recurve out to sea and not affect any land areas--expect perhaps Bermuda.

Jeff Masters

Updated: 8:52 PM GMT en Septiembre 11, 2006

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Hurricane Florence lashes Bermuda

By: JeffMasters, 1:32 PM GMT en Septiembre 11, 2006

Hurricane Florence is lashing Bermuda with winds just below hurricane force. The Bermuda airport at 10:55am local time had sustained winds of 66 mph, gusting to 83 mph. The airport is at the extreme eastern end of the island, and the large eye of Florence is passing just to the west. Thus, the western end of the island may be experiencing much higher winds. Bermuda is now feeling the worst Florence has to dish out, and residents can rest assured that a repeat of the pounding delivered by Category 3 Hurricane Fabian in 2003 will not occur. The primary threat from Florence is an expected 6-8 foot storm surge, topped by large battering waves up to 20 feet high. Florence's winds should cause relatively minor damage. Bermuda's infrastructure is well able to withstand winds of Category 1 force, since much of the utility lines are buried underground, and the building codes demand that structures be able to withstand 110 mph Category 2 hurricane winds.

Florence's appearance on satellite imagery has degraded considerably this morning, probably due to an increase in wind shear to 20 knots. The eye is no longer visible, and the upper level outflow is not as impressive. The Hurricane Hunters reported a large gap on the south side of the eyewall on their recent passes, and this can be seen on the Bermuda radar (Figure 1) and the Bermuda radar animation. The Bermuda radar failed at 4:07am EDT this morning.


Figure 1. Last radar image of Florence at 4:07am EDT (10:07 GMT) before the radar failed.

Although Florence is weakening, she will continue to be a prodigious wave maker. Florence's large swath of tropical storm force have been blowing for many days over a huge stretch of ocean. High ocean swells will continue to impact the U.S. East Coast and Canadaian Maritime provinces the next two days. Five to ten foot seas will be common in many nearshore areas on Tuesday. The wave height forecast animation from the global wave model run by the National Weather Service is most impressive, and predicts wave heights up to 30 feet offshore the Newfoundland coast on Tuesday. Florence is expected to gradually weaken as wind shear increases and ocean temperatures decrease, and will pass close or over Newfoundland later this week as a powerful extratropical storm with 60 mph winds.

Bermuda's next worry: Tropical Depression Seven
Florence's acceleration to the north has allowed the area of disturbed weather a few hundred miles northeast of the Lesser Antilles Islands a chance to develop. Visible satellite imagery shows improved organization, and satellite classification of the storm's intensity already put this system at tropical storm strength. A QuikSCAT pass from 5:26am EDT showed numerous wind vectors in the 40-55 mph range, but confined to the southeast side of the circulation center. The Hurricane Hunters will investigate this system at 2pm EDT today. NHC may wait until then to decide whether or not to upgrade this system to Tropical Storm Gordon. Wind shear has fallen to just 10 knots, the waters are a warm 29C, and some continued development is likely today. Tropical Depression Seven is likely to follow a track similar to Florence, and may be a threat to Bermuda.

Bermuda's worry after that: a new African wave
A strong tropical wave with impressive rotation and plenty of intense thunderstorm activity is emerging from the coast of Africa today. Several of the reliable computer models are forecasting that this will develop into a tropical storm or hurricane that heads westward across the Atlantic. Wind shear is a low 10 knots, and water temperatures are warm. If this system does develop, it would likely recurve out to sea and not affect any land areas--expect perhaps Bermuda. However, it is far too early to be confident of this.

Jeff Masters

Updated: 2:39 PM GMT en Septiembre 11, 2006

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Bermuda braces for Hurricane Florence

By: JeffMasters, 2:16 PM GMT en Septiembre 10, 2006

Today marks the peak day of the Atlantic hurricane season, and we've got the second hurricane of the season to watch now. Hurricane warnings are flying in Bermuda, and the island is bracing for what may be a direct hit by a Category 2 Hurricane Florence on Monday. Florence has an impressive appearance on satellite imagery this morning, with a large 50-mile diameter eye, an outflow channel at upper levels well established to the north, and a smaller one to the east. Given the very large size of the eye, it appears likely that at least a portion of Bermuda will be affected by the eyewall when Florence makes its closest approach Monday. Satellite intensity estimates are steadily increasing, but we'll have to wait until the Hurricane Hunters arrive back at the storm around 2pm EDT this afternoon to see how much intensification has occurred. The last Hurricane Hunter mission departed the storm at 3:30am EDT this morning. One can see some impressive rain bands enveloping the island on Bermuda radar and the Bermuda radar animation.


Figure 1. Latest satellite image of Florence, updated every 1/2 hour.

Florence has a very large swath of tropical storm force winds that have been blowing for many days over a huge stretch of ocean. These factors, when combined with the storm's expected intensification into a Category 2 hurricane, will create very high ocean swells that will impact the entire Atlantic coast from the Lesser Antilles to Canada. The highest seas can be expected from North Carolina to Newfoundland, with five to ten foot seas common in many nearshore areas. Twelve foot seas are expected off Cape Hatteras by Tuesday. The wave height forecast animation from the global wave model run by the National Weather Service is most impressive, and predicts wave heights up to 30 feet offshore the Newfoundland coast on Tuesday. Bermuda can expect waves of 15-25 feet on top of a 6-8 foot storm surge on Monday when the center of Florence passes.

Elsewhere in the tropics
An area of disturbed weather 900 miles east-southeast of Florence has a pronounced surface spin that one can see on visible satellite imagery, and was declared "Invest 93L" by NHC on Saturday. Wind shear has fallen to just 10 knots over this disturbance today, and some slow development is possible as it follows the a track similar to Florence. This storm may be a threat to Bermuda, but probably nowhere else.

There are no other threat areas in the Atlantic to discuss. The computer models forecast a new development off the coast of Africa by the middle of next week, but anything developing in this region is likely to recurve out to sea.


Figure 2. Preliminary model tracks for Invest 93L, 900 miles east-southeast of Florence.

Hurricanes and Bermuda
Hurricanes and Bermuda are no strangers. Since 1551, at least 65 tropical storms and hurricanes have hit the island. Twenty-five of these were major hurricanes. In the past century, the most severe hurricane to hit was the Havana-Bermuda Hurricane of October 22, 1926. This Category 4 storm struck the island with 135 mph winds and killed 88 sailors on a British war ship moored in the harbor that capsized and sank. Since the naming of hurricanes commenced in 1950, the only Bermuda hurricane to gets its named retired was Hurricane Fabian, which struck the island as a category 3 hurricane on September 5, 2003. According to NHC's final report on Hurricane Fabian, the hurricane's eye scraped the west side of the island, bringing the storm's worst winds in the right front quadrant over the island. Sustained winds of 115 mph and a storm surge of 10 feet caused over 300 million in damage and killed four. Battering waves 20-30 feet high affected the south shore of the island.

PBS television show tonight
Some Public television stations will be carrying the show, "Anatomy of a Hurricane", tonight at 10:30pm. Here's their description of the show:

This documentary program goes inside the National Hurricane Center in Miami, Florida, during the 2004 hurricane season. Tune in to get a revealing look at the stressful work of the dedicated staff who deal with unique and unexpected challenges and struggle to make the most accurate predictions. (CC, Stereo)
http://www.pbs.org/stationfinder/stationfinder_relocalize.html

It should be a great look inside at what goes on at the NHC during a big storm!

I'll have an update late tonight or early Monday morning.

Jeff Masters

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Florence near hurricane strength

By: JeffMasters, 3:48 PM GMT en Septiembre 09, 2006

Florence has begun the long-expected intensification phase that was forecast for the past week, much to the relief of hurricane forecasts who worried that their basic understanding of hurricane intensification processes was flawed--but much to the dismay of residents of Bermuda. Bermuda is under a tropical storm warning today, and this will almost certainly be upgraded to a hurricane warning tonight. Florence managed to get rid of its large lopsided shape that was inhibiting organization, and adopt a more a symmetric cloud pattern conducive for development. Satellite imagery this morning shows good outflow to the north and east, but no eye yet. Satellite intensity estimates already put Florence at hurricane strength, but the NHC is waiting until the Hurricane Hunters arrive in the storm at 2pm EDT to verify hurricane force winds exist before upgrading Florence to a hurricane. The forecast track of Florence puts the storm over or just west of Bermuda on Monday, and that island is bracing for its worst weather day since Hurricane Fabian of 2003 hit the island as a Category 3 hurricane with 115 mph winds.

Florence has a very large swath of tropical storm force winds that have been blowing for many days over a huge stretch of ocean. These factors, when combined with the storm's expected intensification into a Category 2 hurricane, will create very high ocean swells that will impact the entire Atlantic coast from the Lesser Antilles to Canada. Five to ten foot seas will be common in many nearshore areas, and the wave height forecast from the global wave model run by the National Weather Service predicts wave heights of 15-20 feet offshore the mid-Atlantic and New England coasts by Tuesday. Bermuda can expects waves of 15-25 feet on top of a 6-8 foot storm surge on Monday when the center of Florence passes.


Figure 1. Forecast wave heights for Monday night at 8pm EDT, from the Global Wave Model of the NWS.

Elsewhere in the tropics
An area of disturbed weather 900 miles east-southeast of Florence has a pronounced surface spin one can see on visible satellite imagery, and was declared "Invest 93L" last night by NHC. This disturbance is under 40 knots of vertical wind shear from its big sister, Florence, and has a limited chance of survival. If it does survive, it is likely to follow its sister northward then northeastward, out to sea. There are no other threat areas to discuss. The computer models forecast a new development off the coast of Africa by the middle of next week, but anything developing in this region is likely to recurve out to sea.


Figure 2. Preliminary model tracks for Invest 93L, 900 miles east-southeast of Florence.

I'll have an update Sunday morning by 10:15am EDT.

Jeff Masters

Updated: 3:51 PM GMT en Septiembre 09, 2006

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El Nio is coming!

By: JeffMasters, 2:04 PM GMT en Septiembre 08, 2006

An El Nio is on the way, according to the latest El Nio discussion posted September 7 by NOAA's Climate Prediction Center. A steady warming of the waters in the Equatorial Pacific near the coast of South America, combined with stronger than usual westerly winds over the Equatorial Pacific, point toward the emergence of a weak El Nio episode beginning in October or November. Certainly the above-normal hurricane activity in the Eastern Pacific and the appearance of record-breaking Hurricane Ioke in the Central Pacific were signs of a coming El Nio; intense hurricanes in those regions are highly correlated with the above normal ocean temperatures of a developing El Nio event. When the Equatorial Eastern Pacific waters warm to above 0.5C above normal for three consecutive months, an official El Nio is at hand. The ocean temperatures in this region are already at that level, and forecast to increase further over the next few months. An El Nio event can have far-reaching effects on global climate and Atlantic hurricane season activity.


Figure 1. Departure of Sea Surface Temperature (SST) from normal for September 2006 (top) and May 2006 (bottom). Note the departure of SST from normal affecting the Equatorial Eastern Pacific waters. In May, these waters were much cooler than normal, thanks to the lingering effects of the La Nia episode that ended in May. Now in September, these water have warmed dramatically, and may signal the beginning of an El Nio episode.

El Nio and climate change
A trend to El Nio at this time of year is unusual; May or June are the typical months that El Nio starts to develop. While the Climate Prediction Center expects that this will be a weak El Nio, the unusual timing of this event puts us in relatively uncharted territory. Since 1950, only one El Nio has started in the Fall, the El Nio of 1968. This event was an average El Nio, with a peak SST warming in the East Pacific of 1.0 C. For comparison, the warming was 2.3-2.5 C in the record El Nio events of 1997-98 and 1982-83. The unusual timing of the 2006 El Nio event comes on the heels of the unusual timing of the La Nia event that ended in May. The 2006 La Nia started very late--no La Nia of similar magnitude had ever formed in the middle of winter, as this one did. One may legitimately ask if these events might be linked to human-caused climate change. I am concerned that this might be the case, but we don't have a long enough record of historical El Nio events to know. Up until 1975, La Nia events and El Nio events used to alternate fairly regularly with a period of 2-7 years. Between 1950 and 1976 there were seven El Nio events and seven La Nia events. Since 1976, El Nio events have been approximately twice as frequent as La Nia events, with ten El Nio events and only six La Nias. Some researchers have speculated that this is due to the effects of global warming causing a new "resonance" in the climate system. If so, this is one way in which global warming may end up causing a decrease in Atlantic hurricane activity over the coming decades, since the increased wind shear over the Atlantic during El Nio events greatly reduces the number and intensity of these storms.

Effect of El Nio on hurricane season
As most of you know, El Nio conditions put a major damper on both the number and intensity of Atlantic tropical cyclones. This is primarily due to increased wind shear. The upper air winds that develop when one heats the Equatorial Eastern Pacific waters tend to blow from west to east over the Atlantic at high speed. Since the tropical Atlantic trade winds near the surface typically blow the opposite direction, this creates a lot of shear that makes it difficult for a tropical cyclone to survive. Thus far in September, wind shear over the tropical Atlantic has been about normal, so there is no sign that a developing El Nio is suppressing hurricane activity yet. However, if the Climate Prediction Center is right, we can expect an earlier than usual end to hurricane season in the Atlantic, and a quiet November and December--unlike last year! El Nios can be long lived, and if the forecast El Nio for this year develops as expected, it will probably last through the hurricane season of 2007, suppressing hurricane activity next year.

Effect of El Nio on the coming winter
In the U.S., El Nio winters typically have above average rainfall across the southern tier of states, particularly along the Gulf of Mexico and California coasts. Temperatures tend to be warmer than average across the northern tier of states. Temperatures are typically cooler across the southern tier of states, due to increased cloud cover. For more info on El Nio's typical wintertime effects, see the Wikipedia El Nio page or the Climate Prediction Center winter precipitation and temperature impacts page.

Florence
I can basically repeat my blog for the past four days on Florence. Florence is a huge but disorganized tropical storm. Despite the fact that wind shear has decreased to 5-10 knots, Florence shows little sign of intensification. QuikSCAT data from this morning at 5:02am showed top winds of about 45 mph in some widely scattered pockets to the north of the center. There is still some dry air for the storm to contend with, but SSTs are a very warm 29 C and the models are still insisting the storm should intensify. It is a mystery why the tropical atmosphere has been so resistant to tropical cyclone intensification this year. It's a happy mystery for Bermuda, which figures to have a very close encounter with the core of the storm on Monday. Given Florence's continued refusal to intensify despite our expectations, I'd be surprised if the storm affected Bermuda as anything stronger than a Category 1 hurricane. Newfoundland also needs to keep an eye on Florence; some of the models are predicting she could brush that island later next week. The Hurricane Hunters are due to fly their first mission into Florence at 2am EDT Saturday.

Elsewhere in the tropics
There are no other threat areas to discuss. The stationary front off the Carolina coast may spawn another low pressure system that will try to develop into a tropical depression over the next two days, but any storm here will move quickly northeast out to sea and not affect North Carolina. The long-range GFS is predicting that two more tropical storms may develop off the coast of Africa over the next two weeks, but any storms that develop here are likely to recurve out to sea and never affect land.

My next update will be Saturday morning.

Jeff Masters

Updated: 4:10 PM GMT en Septiembre 08, 2006

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Little change to Florence

By: JeffMasters, 2:11 PM GMT en Septiembre 07, 2006

Florence continues to struggle with 10-15 knots of wind shear today, and doesn't appear any stronger than yesterday. QuikSCAT satellite data from this morning at 5:26am showed only a few patches of 50 mph winds. Compounding Florence's troubles has been the presence of some dry air at mid levels, which Dr. Jason Dunion of NOAA's Hurricane Research Division pointed out in a blog yesterday.

The big questions with Florence are, will she intensify, and how close will she pass to Bermuda? Well, the intensity forecast remains the same, with the upper level low to the west forecast to move off and allow a lower shear environment for Florence to intensify in. The GFDL model intensifies Florence to a strong Category 2 hurricane at her closest approach to Bermuda on Monday. However, Florence has thus far resisted intensification, so a more conservative intensity forecast may be in order.


Figure 1. QuikSCAT satellite winds estimates for Thursday morning, September 8, 2006. Image credit: NOAA/NESDIS.

All the computer models are unanimous in bringing Florence close to Bermuda, then out to sea, missing both the U.S. and Canada (although a sideswipe of Newfoundland is possible). It would be a major surprise if Florence hit the U.S. We can, however, expect plenty of heavy surf and minor beach erosion along the East Coast next week if Florence does intensify into a Category 2 hurricane. Bermuda is a small target in a big ocean, and I expect that island will escape a direct hit from Florence. Florence is a very large storm, though, and tropical storm force winds will probably affect the island Sunday through Tuesday. The Hurricane Hunters are scheduled to make their first flight into Florence Friday afternoon.

Florence strangles her little brother
Tropical disturbance 91L, about 800 miles east-southeast of Florence, is no longer a threat to develop. The disturbance's close proximity to its big sister has proved too much for the disturbance, which now has very little spin and just a few thunderstorms. There is a small chance 91L could separate from Florence on Sunday and make a comeback, just northeast of the northernmost Lesser Antilles Islands.

Carolinas disturbances
A stalled cold front off the Carolina coast spawned a low-pressure area yesterday that moved quickly northeast and is now northeast of Cape Hatteras, North Carolina. This low is under 30 knots of wind shear and is transitioning into an extratropical storm, and is not a threat to become a tropical storm. This morning's 7:07am EDT QuikSCAT pass (Figure 1) does show one orange 30 knot (34 mph) wind barb, so this low is of tropical depression strength. Another area of low pressure off the South Carolina coast this morning is poised to repeat what yesterday's system did. This area of disturbed weather had winds up to 40-50 mph in some heavy squalls in the QuikSCAT satellite pass at 7:13am EDT today. The system does have some potential to develop into a tropical depression today as it scoots northeast just offshore the North Carolina coast. However, it will probably not have enough time to develop, and will become extratropical by Friday afternoon over the waters to the northeast of Cape Hatteras.

Huge extratropical storm hits Brazil
Perhaps the most damaging storm in the world this September was not Ernesto in the Atlantic, John in Baja, nor Ioke on Wake Island. Brazil had an usually intense wintertime extratropical cyclone bring wind gusts to hurricane force along the coast of Brazil's southernmost state, Rio Grande do Sul, on September 2. Winds of 101 km/h in that state's capital city of Porto Alegre tore roofs of of houses, downed trees and powerlines, and caused power outages to half a million people. Luiz Fernando Nachtigall, Chief Meteorologist for MetSul Meteorologia Weather Center, sent me a link to some damage photos from the event. After the wind event, the storm brought the most widespread snow event in Southern Brazil since 1994. It snowed in 62 cities.


Figure 1. Visible satellite image of the September 2, 2006 extratropical cyclone that affected Brazil. The storm had a minimum pressure of 980 mb, similar to what one finds in a Category 1 hurricane! Extratropical cyclones that move over warm ocean currents can start to exhibit characteristics of hurricanes, as I described in my February blog, Flying into a record Nor'easter. Extratropical storms of this intensity happen fairly regularly off the Northeast U.S. coast, but are extremely rare along the Brazilian coast. Image credit: MetSul Meteorologia Weather Center.

Next update
I'll have an update this afternoon or Friday morning.

Jeff Masters

Updated: 4:41 PM GMT en Septiembre 07, 2006

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Florence battles dry air; Hurricane Hunters investigate new disturbance

By: JeffMasters, 11:22 PM GMT en Septiembre 06, 2006

Florence continues to struggle with wind shear today, and is managing just a slow intensification. Compounding Florence's troubles is the presence of some dry air at mid levels, as revealed this afternoon in the appearance of arc clouds at the surface. Dr. Jason Dunion of NOAA's Hurricane Research Division has posted a blog this evening showing some examples of these arc clouds. What happens is that a ribbon of dry air at mid levels gets sucked into a thunderstorm inside of Florence, which then creates a strong downdraft that leaves its mark at the surface as an arc cloud that expands out in a semicircle.

Hurricane Hunters in the air
The Air Force Hurricane Hunters are in the air off the North Carolina coast investigating a new area of concern that developed along the old cold front off the Carolina coast. So far, they've found peak winds of 20 mph at flight level (500 feet), but they aren't done investigating the system yet. This storm, designated "Invest 92L" by NHC this afternoon, is expected to move rapidily northeast away from North Carolina and become an extratropical storm Thursday night. If the Hurricane Hunters find a tropical depression, I'll post an update tonight.


Figure 1. Preliminary model tracks for Invest 92L, a tropical disturbance off the North Carolina coast.

Jeff Masters

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Florence still a weak tropical storm

By: JeffMasters, 1:54 PM GMT en Septiembre 06, 2006

Florence still looks pretty disorganized, with a large, sloppy center and some clumps of heavy thunderstorms on the east side. Wind shear of 10-20 knots due to upper-level westerly winds is causing much of this disorganization. Part of Florence's struggles are due to her inability to overcome her initial indecision on where her center of circulation should be. In any case, Florence remains a weak tropical storm today. Only slow intensification should happen today. This morning's QuikSCAT satellite pass found only 40 mph winds in Florence, although it did miss sampling the most intense portion of the storm.

Intensity forecast
The winds shear forecast is a bit more uncertain today. An upper-level low to the west of Florence that is creating the shear is forecast to move away, allowing Florence to intensify to a hurricane (and possibly a major hurricane) over the next four days. However, the speed with which this upper low may move off is uncertain, and a slower than expected movement way will keep significant winds shear over Florence. The disturbance about 800 miles to the east-southeast may also steal some energy from Florence over the next few days.

Track forecast
The computer models had a better-defined storm to track with their more recent runs, and should be reasonably reliable today. The disturbance "Invest 91L" about 800 miles to the east-southeast of Florence may still cause some trouble if it develops into a tropical depression, however. When two storms get within 13 degrees of arc of each other (900 miles), they can interact (the Fujiwhara effect), causing difficulties in the track and intensity forecasts.

The models have a very believable scenario where Florence moves north of the Lesser Antilles Islands, then turns northward in response to a trough of low pressure swinging across the Eastern U.S. four days from now. On this trajectory, Florence would only be a threat to Bermuda and perhaps the Maritime provinces of Canada. When one consults the map of historical paths of September tropical storms that have tracked near Florence's current position, we see that only one of these previous storms managed to hit the U.S. East Coast. I will be surprised (though not amazed) if Florence does manage to strike the U.S.

Florence's little brother
Tropical disturbance 91L, about 800 miles east-southeast of Florence, is a little less organized than yesterday. The disturbance's close proximity to its big sister is probably hampering its development. Some of the computer models predict that 91L will never escape the shadow of big sister, following her on a recurving path out to sea between Bermuda and the U.S. East Coast and never developing into a tropical storm. However, some of the models predict that when Florence gets pulled sharply north, this will open up enough separation between the two storms to allow 91L to split away and intensify.


Figure 1. Preliminary model tracks for Invest 91L, the tropical wave 800 miles to the ease-southeast of Florence.

Carolinas
A stalled cold front off the Carolina coast has spawned a low-pressure area with a clump of intense thunderstorms a few hundred miles off the Florida/Georgia coast. This low is expected to track north-northeast and pass near the Outer Banks of North Carolina Thursday morning. A second low may develop in a similar location on Thursday and pass by the Outer Banks on Friday morning. Neither of these lows have enough time to develop into tropical depressions.

Ioke
Ioke is finally gone! It turned into a powerful extratropical storm with 60 mph winds yesterday over the ocean waters east of Japan.

Next update
I'll have an update Thursday morning, unless there's something interesting to report on this afternoon.

Jeff Masters

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Florence is born

By: JeffMasters, 3:47 PM GMT en Septiembre 05, 2006

Tropical Depression Six got enough heavy thunderstorm activity surrounding its center to be upgraded to Tropical Storm Florence at 11am EDT. Florence doesn't look much like a tropical storm on satellite imagery, with a very broad center and the main thunderstorm activity well removed from the center. Maximum winds of 30 knots (35 mph) were seen on this morning's 4:33am EDT QuikSCAT pass (Figure 1), which are just below tropical storm force. However, the winds in Figure 1 were taken from the low-resolution 25 km QuikSCAT product, and the higher-resolution 12.5 km QuikSCAT winds did show a few areas of tropical storm force winds. These stronger winds were given as justification for upgrading to a tropical storm. Given the disorganization of the storm and marginal tropical storm force winds on QuikSCAT, the system could have just as easily been held as a tropical depression for one more advisory. The 12.5 km QuikSCAT product is noisier and more prone to error than the standard 25 km product, and is not always used by NHC to make a judgement about upgrading to a tropical storm.

Florence has managed to consolidate the two circulation centers it was struggling with yesterday into one large circulation center. It will probably take another day before the winds tighten up around the center and Florence can begin any substantial intensification. Interfering with this process will be about 10-15 knots of shear and some dry air to the north. The shear should lessen by Thursday, potentially allowing Florence to become a hurricane.

The computer models all forecast that Florence will pass north of the Lesser Antilles Islands, although it is too far in the future to be highly confident of this forecast. A complicating factor is the development of a new disturbance about 800 miles to the east-southeast. This new disturbance, officially designated "Invest 91L" this morning by NHC, is close enough to alter both the strength and track of TD 6. Anytime two storms get within 13 degrees of arc of each other (900 miles), the two storms tend to rotate around a common center (the Fujiwhara effect). The computer models do make some allowances for this effect, but are not very good at handling it. For this reason, one should be suspicious of the track and intensity forecasts for Florence and 91L as long as they are so close. The intensities of both storms can also change as a result of the interaction, with both storms intensifying at a slower rate than they otherwise would, or one storm growing at the expense of the other. If the two storms approach within about 7 arc-degrees of each other (480 miles), this is considered the "zone of death" where one cyclone will surely destroy the other. The surviving storm will not be a "superstorm" that has the combined size and strength of the two storms, however.

The long-range GFS model forecast continues to show Florence becoming a powerful hurricane that threatens Bermuda, but recurves out to sea well east of the U.S. East Coast. Again, it is too early to be confident of this forecast. Keep in mind that early model forecasts are often very unreliable. That is because the center is not well established and often relocates, and that subtle difference can make major
track changes. Also, the global models such as the GFS, UKMET, and NOGAPS represent a weak storm as a very diffuse entity, and that causes problems for the global models and the "zoomed in" models like the GFDL that use a global model (the GFS) as their starting points. Be wary of the track forecasts until the system becomes more established. Tomorrow morning we should have a better idea of the models' reliabilty, since Florence should be better established.


Figure 1. QuikSCAT satellite winds from 4:33am EDT Tuesday September 5 2006. Wind speed and direction are coded according to the standard station model, and are color coded (in knots) according to the color scale at the upper right (10 knots = 11.5 mph). Black winds barbs occur where there is rain, and one cannot trust the wind speeds measured in those areas. Tropical storm force winds (35 knots) are colored red and need to have 3 long bars and one short bar attached to the end of the "barb"; there is one barb like this on the east side of TD 6, but it is pointing a different direction than the other barbs around it, and is surrounded by rain-contaminated (black) barbs. One should be suspicious of the accuracy of this lone tropical storm force wind barb.


Figure 2. Preliminary model tracks for Invest 91L, a well-organized tropical wave a few hundred miles west of the Cape Verde Islands.

Cape Verdes Islands tropical wave
A strong new tropical wave emerged from the coast of Africa Saturday and is a few hundred miles west-southwest of the Cape Verde Islands. The wave has a closed circulation, and visible satellite imagery from this morning shows an increase in thunderstorm activity on the west side. The wave is over warm water and is under a modest 10 knots of wind shear, and could be Tropical Depression Seven by Wednesday. Due to its more southerly starting position, this system is more likely to be a threat to land than Florence.

Carolinas
North Carolina is still suffering flooding problems from Ernesto. Where Ernesto came ashore at Cape Fear, North Carolina, the North Cape Fear River is at 16.6 feet, and flood stage is only 10 feet. This is the second highest flood on this river; only Hurricane Floyd of 1999 caused a higher flood. With a strong cold front expected to move through tonight and stall offshore, North Carolina will receive another 1-2" of rain that will make flooded areas slow to recover. Once this cold front does stall over the warm Gulf Stream waters, we need to watch the area off the Carolina coast for possible tropical storm development.

Ioke
Ioke continues its slide into oblivion, and is now a mere tropical storm. Ioke is caught in a large trough of low pressure that is weakening it and recurving it out to sea. Ioke is not a threat to any land.

Next update
I'll have an update Wednesday morning, unless there's something interesting to report on this afternoon.

Jeff Masters

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Tropical Depression Six and a new disturbance interact

By: JeffMasters, 1:42 PM GMT en Septiembre 05, 2006

Tropical Depression Six is not yet a tropical storm, as evidenced by the maximum winds of 25-30 knots (30-35 mph) seen on this morning's 4:33am EDT QuikSCAT pass (Figure 1). TD 6 has managed to consolidate the two circulation centers it was struggling with yesterday into one large circulation center. The storm's maximum winds are occurring in bands well removed from this broad center, and it will probably take another day before the winds tighten up around the center and the TD 6 can intensify into a tropical storm. Interfering with this process will be about 10-15 knots of shear and some dry air to the north.

The computer models all forecast that TD 6 will pass north of the Lesser Antilles Islands, although it is too far in the future to be confident of this forecast. A complicating factor is the development of a new disturbance about 800 miles to the east-southeast. This new disturbance, officially designated "Invest 91L" this morning by NHC, is close enough to alter both the strength and track of TD 6. Anytime two storms get within 13 arc-degrees of each other (900 miles), the two storms tend to rotate around a common center (the Fujiwhara effect). The computer models do make some allowances for this effect, but are not very good at handling it. For this reason, one should be suspicious of the track forecasts for TD 6 and 91L as long as they are so close. The intensities of both storms can also change as a result of the interaction, with both storms intensifying at a slower rate than they otherwise would, or one storm growing at the expense of the other. If the two storms approach within about 7 arc-degrees of each other (480 miles), this is considered the "zone of death" where one cyclone will surely destroy the other. The surviving storm will not be a "superstorm" that has the combined size and strength of the two storms, however.

The long-range GFS model forecast continues to show TD 6 becoming a powerful hurricane that threatens Bermuda, but recurves out to sea well east of the U.S. East Coast. Again, it is too early to be confident of this forecast, given the interactions that may occur with 91L and the inherent uncertainties in long-range hurricane track forecasts. The wind shear later this week is forecast to drop significantly, so if TD 6 manages to survive the next 36 hours, it is likely to become a hurricane.


Figure 1. QuikSCAT satellite winds from 4:33am EDT Tuesday September 5 2006. Wind speed and direction are coded according to the standard station model, and are color coded (in knots) according to the color scale at the upper right (10 knots = 11.5 mph). Black winds barbs occur where there is rain, and one cannot trust the wind speeds measured in those areas. Tropical storm force winds (35 knots) are colored red and need to have 3 long bars and one short bar attached to the end of the "barb"; there is one barb like this on the east side of TD 6, but it is pointing a different direction than the other barbs around it, and is surrounded by rain-contaminated (black) barbs. One should be suspicious of the accuracy of this lone tropical storm force wind barb.


Figure 2. Preliminary model tracks for Invest 91L, a well-organized tropical wave a few hundred miles west of the Cape Verde Islands.

Cape Verdes Islands tropical wave
A strong new tropical wave emerged from the coast of Africa Saturday and is a few hundred miles west-southwest of the Cape Verde Islands. The wave has a closed circulation, and visible satellite imagery from this morning shows an increase in thunderstorm activity on the west side. The wave is over warm water and is under a modest 10 knots of wind shear, and could be Tropical Depression Seven by Wednesday. Due to its more southerly starting position, this system is more likely to be a threat to land than TD 6.

Carolinas
North Carolina is still suffering flooding problems from Ernesto. Where Ernesto came ashore at Cape Fear, North Carolina, the North Cape Fear River is at 16.6 feet, and flood stage is only 10 feet. This is the second highest flood on this river; only Hurricane Floyd of 1999 caused a higher flood. With a strong cold front expected to move through tonight and stall offshore, North Carolina will receive another 1-2" of rain that will make flooded areas slow to recover. Once this cold front does stall over the warm Gulf Stream waters, we need to watch the area off the Carolina coast for possible tropical storm development.

Ioke
Ioke continues its slide into oblivion, and is now a mere tropical storm. Ioke is caught in a large trough of low pressure that is weakening it and recurving it out to sea. Ioke is not a threat to any land.

Next update
I'll have an update Wednesday morning, unless there's something interesting to report on this afternoon.

Jeff Masters

Updated: 1:51 PM GMT en Septiembre 05, 2006

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Tropical Depression Six reorganizing

By: JeffMasters, 12:59 AM GMT en Septiembre 05, 2006

Tropical Depression Six is having trouble making up its mind where its center should be. The center it organized around is getting competition from another center of circulation about 400 miles to the southwest, as seen in the latest QuikSCAT image posted at 8:30pm EDT tonight (Figure 1). The large area of thunderstorms about 400 miles southwest of TD 6, formerly designated "Invest 98L", is still there, and is causing major difficulties for TD 6, which can't make up its mind which center to consolidate around. Until the depression resolves this conflict, you can throw all the model runs out the window--they will not be able to resolve the double circulation centers. TD 6 may well decide to organize around the old Invest 98L center to the southwest, which would pull the forecast tracks further south towards the Lesser Antilles Islands. Another wind card is the presence of the new tropical wave to the east of TD 6, near the Cape Verde Islands. This wave is close enough to TD 6 that it may be stealing some energy from the depression and inhibiting its intensification. Again, the models will not be able to deal with this interaction with another circulation nearby.

Despite this conflict, TD 6 has grown stronger since this morning--there are many more red 40 mph wind vectors visible in the evening QuikSCAT pass (Figure 1) compared to the morning pass (Figure 2). It will be interesting to see if NHC upgrades the system to Tropical Storm Florence at 11pm, or decides to wait to see which center TD 6 forms around.


Figure 1. QuikSCAT satellite winds from 5pm EDT Monday evening, September 4, 2006. Wind speed and direction are coded according to the standard station model, and are color coded (in knots) according to the color scale at the upper right (10 knots = 11.5 mph). Black winds barbs occur where there is rain, and one cannot trust the wind speeds measured in those areas. Tropical storm force winds (35 knots) are colored red, brown, or purple; one can see many red wind barbs in TD 6. Note the increased winds (orange barbs, 25-30 knots) around Invest 98L, compared to the morning QuikSCAT pass (below).


Figure 2. QuikSCAT satellite winds from 5am EDT Monday morning, September 4, 2006. One can see one red wind barb in TD 6.

Cape Verdes Islands tropical wave
The wave just west of the Cape Verdes Islands has a closed circulation, which can be seen on QuikSCAT imagery from this morning and this evening (Figures 1 and 2). The wave's winds have not increased between the two passes by the satellite, and TD 6 may be inhibiting the wave's development. The wave is under a modest 10 knots of wind shear, and has some potential for slow development over the next few days.

Next update
I'll have an update Tuesday morning.

Jeff Masters

Updated: 1:04 AM GMT en Septiembre 05, 2006

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Tropical Depression Six almost has its name

By: JeffMasters, 3:17 PM GMT en Septiembre 04, 2006

Tropical Depression Six is nearly a tropical storm, as evidenced by winds of 25-35 knots seen in this morning's QuikSCAT pass (Figure 1). Visible satellite imagery shows an increase in curved low-level rain bands forming, and satellite estimates of the storm's strength already put it at minimal tropical storm strength (40 mph). The computer models all forecast that this storm will most likely pass north of the Lesser Antilles Islands, although that is too far in the future to be confident of this forecast. The long-range GFS model forecast continues to show TD 6 becoming a powerful hurricane that threatens Bermuda, but recurves out to sea well east of the U.S. East Coast. Wind shear over the system is low, about 10 knots, but may increase a bit to 10-15 knots over the next two days. After that, wind shear should die down and a large anti-cyclone build over the storm, potentially allowing it to intensify into a hurricane. The large area of thunderstorms about 400 miles southwest of TD 6, formerly designated "Invest 98L", is still there, and may be slowing down the intensification of TD 6. As TD 6 grows, it should be able to absorb the remnants of 98L.


Figure 1. QuikSCAT satellite winds from Monday morning, September 4 2006. Wind speed and direction are coded according to the standard station model, and are color coded (in knots) according to the color scale at the upper right (10 knots = 11.5 mph). Black winds barbs occur where there is rain, and one cannot trust the wind speeds measured in those areas. Tropical storm force winds (35 knots) are colored red, brown, or purple; one can see one red wind barb in TD 6.

Cape Verdes Islands tropical wave
A strong new tropical wave emerged from the coast of Africa Saturday and is a few hundred miles west-southwest of the Cape Verde Islands. The wave has a closed circulation, which can be seen on QuikSCAT imagery from this morning (Figure 1). The thunderstorm activity associated with the wave is limited and disorganized. The wave is under a modest 10 knots of wind shear, and has some potential for slow development over the next few days.

Caribbean tropical wave
The small tropical wave that moved into the Caribbean yesterday has become much less organized and is no longer a threat to develop. The remains of "Invest 99L" can be seen on the QuikSCAT image from this morning (Figure 1) as a small area of black wind barbs (which denote rain) between South America and Hispaniola. There are a few yellow wind barbs in there, representing winds of 20-25 knots. The wind barbs mostly point the same way, with only a small change in wind direction in the wave. This is the sign of a weak tropical wave. A sharp change in wind direction occurs in strong tropical waves, with this strong wind shift eventually amplifying into a complete circular rotation if the wave develops into a tropical depression.

John is dead
The remains of Hurricane John are about 2/3 of the way up the Baja Peninsula, and will spread heavy rains of up to 1-3 inches into Arizona, New Mexico, and western Texas over the next few days. John destroyed many roads and took the roofs off of at least 150 houses in Mexico's Baja.

Typhoon Ioke
Typhoon Ioke is now barely a typhoon, with top winds of 75 mph. Ioke is caught in a large trough of low pressure that is weakening it and recurving it out to sea. Ioke is not a threat to any land.

Next update
I'll have an update Tuesday morning. Have a good Labor Day, everyone!

Jeff Masters

Updated: 3:17 PM GMT en Septiembre 04, 2006

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New depression forming?

By: JeffMasters, 1:05 PM GMT en Septiembre 03, 2006

A tropical wave near 13N 39W, midway between Africa and the Lesser Antilles Islands, appears to be developing into a tropical depression. This wave was declared "Invest 90L" last night by NHC. The wave has a pronounced spin, and plenty of heavy thunderstorm activity surrounding it. This activity is fragmented and not concentrated near the center of circulation, but it gradually getting better organized. At the current rate of organization, formation of a tropical depression seems likely by tonight or Monday morning.

Three of the major models--the GFS, UKMET, and GFDL--do develop this system into a strong tropical storm or Category 1 hurricane by six days from now. The system is moving west-northwest at 10-15 mph, and these models all indicate that the long-range path of the storm will be north of the Lesser Antilles Islands. The GFS predicts the storm will become a powerful hurricane that will recurve a few hundred miles off the U.S. East Coast without hitting land. Wind shear over the system is low, about 10 knots, and the wave is over warm SSTs of 83-86F (28.5-30 C). Wind shear is forecast to remain low over the next few days. A large area of dry air and African dust to the wave's north may be an inhibiting factor, but this is probably to far away at present to be a problem. The large area of thunderstorms about 400 miles west of 90L, formerly designated "Invest 98L", is being absorbed into 90L.


Figure 1. Preliminary model tracks for Invest 98L. These models are described at the NHC web site.

Lesser Antilles tropical wave
A small tropical wave surrounded by a cloud of African dust is moving through the eastern Caribbean this morning. This wave, which NHC has designated "Invest 99L", is tracking west at 15 mph and has a small area of heavy thunderstorms associated with it. A large upper trough of low pressure over Cuba and Hispaniola that is creating about 10-20 knots of shear over 99L, preventing significant development. The trough is expected to weaken and move west over the next few days, potentially creating a low shear environment over most of the Caribbean. This could allow intensification of 99L into a tropical depression by Tuesday at the earliest. NHC has not run any preliminary models for this storm since yesterday.

New wave coming off the coast of Africa
A strong new tropical wave is emerged from the coast of Africa yesterday and is just south of the Cape Verde Islands. The wave has pronounced spin, but the thunderstorm activity associated with it is very disorganized. The wave is under 10-20 knots of wind shear, and has some potential for slow development over the next few days.

Tropical Storm John
Hurricane John spared the most heavily populated areas of Mexico's Baja Peninsula significant damage when it came ashore Friday afternoon on the sparsely populated eastern side of the Peninsula as a Category 2 hurricane with 110 mph maximum winds. Many roads were washed out in the resort towns of Cabo San Lucas and San Jose del Cabo, and helicopter airdrops of food and water were needed for 6000 residents cut off by washed out roads near where the center made landfall. However, no one was killed by the storm. Radar from Guasave shows John is still moving up the Baja Peninsula, spreading heavy rains. John will continue to weaken as it moves northwest along the Baja Peninsula, and should die on Monday. Moisture from the hurricane will likely bring flooding rains to portions of the Southwest early next week.

Typhoon Ioke
Typhoon Ioke is now barely a major storm, with its top winds of 115 mph barely qualifying it as a Category 3. It is forecast to recurve to the north and miss Japan.

Lessons learned from Ernesto
Ernesto may be gone, but its rain, winds, and flood waters still linger over the Eastern U.S. Rain from the storm penetrated all the way to may home in Michigan yesterday, a sure indication of a storm with a major far-reaching impact. Let's summarize two important lessons from the storm:

Lesson 1: This is not the Hurricane Season of 2005! By this time last year, we were already up to the 13th named storm of the season, Maria. Pretty much anytime something could develop, it did, and it usually took the worst possible path. This year, we are only up to the 5th named storm, and the storms have been taking some fortuitous paths. Certainly, we got very lucky with Ernesto--I was convinced that Haiti was in for a major disaster with heavy loss of life, and Ernesto would get his name retired. Hurricane Jeanne (2004) and Hurricane Gordon (1994) were both about the same strength as Ernesto when they hit Haiti, and both storms killed thousands. Yet Ernesto only dumped 2-8 inches of rain on Haiti, an unusually low amount for a Category 1 hurricane. Ernesto also took the longest possible path over land, given its general track, cutting across the Florida Straits without spending much time over water. I'll be full of much less doom-and-gloom for the next storm of this season that threatens land. This is not the Hurricane Season of 2005!

Lesson 2: The forecast track cone is often not big enough. The retiring director of NHC, May Mayfield, says that he wants the epitaph, "Don't look at the center track forecast line, look at the cone of possible tracks" engraved on his tombstone. Well, sometimes even the cone isn't big enough. The cone is based on the average track error in NHC forecasts over the past few years. Nearly half the time, the actual track of a storm will fall outside the cone. If you looked at those early forecasts of Ernesto going into the Gulf of Mexico, the cone did not quite extend all the way to the eventual landfall point at the extreme southern tip of Florida. Track forecasts are getting better--last year's 5-day forecasts were about as accurate as a 3-day track forecast 15 years ago--but there are many situations where the computer models and the human forecasters do poorly.

Next update
I'll have an update Monday morning.

Jeff Masters

Updated: 1:07 PM GMT en Septiembre 03, 2006

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John crunches Baja; two Atlantic systems to watch

By: JeffMasters, 2:34 PM GMT en Septiembre 02, 2006

Hurricane John crunched ashore the eastern side of Mexico's Baja Peninsula last night at 5pm PDT as a Category 2 hurricane with 110 mph maximum winds. The east side of the Baja Peninsula is relatively sparsely populated, and John largely spared the resort towns of Cabo San Lucas and San Jose del Cabo. Radar from Guasave shows John is moving up the Baja Peninsula, and is now battering the capital, La Paz, as a Category 1 hurricane. John will continue to weaken as it moves northwest along the Baja Peninsula, and should die before it reaches the U.S. However, moisture from the hurricane will likely bring flooding rains to portions of the Southwest early next week.


Figure 1. Radar from Hurricane John at landfall, 8:38pm EDT Friday 9/1/06. Image credit: Servicio Meteorologico Nacional of Mexico.

NHC declares a new "invest" on tropical wave in Lesser Antilles
The tropical wave surrounded by a cloud of African dust and dry air that I've been commenting on ever since it left the coast of Africa, is now an official threat. NHC has designated this wave "Invest 99L" this morning. The wave is near 15N 61W, right on top of the Lesser Antilles Islands. It is surrounded by a large cloud of dry air and African dust, but has slowly been able to pump more moisture into its center each night over the past few days as thunderstorm development kicks up then dies away. The thunderstorm activity has picked up considerably this morning, the first time the disturbance has been able to build thunderstorms during the daytime hours. The disturbance is tracking west at 15 mph into a large upper trough of low pressure over Cuba and Hispaniola that is creating about 10-20 knots of shear over 99L. The trough is expected to weaken and move west over the next few days, potentially creating a low shear environment over most of the Caribbean. This could allow intensification of 99L into a tropical depression by Monday.


Figure 2. Preliminary model tracks for Invest 99L. These models are described at the NHC web site.

The mid-Atlantic tropical wave to watch
A tropical wave near 11N 39W, midway between Africa and the Lesser Antilles Islands, was declared "Invest 98L" last night by NHC. However, the wave no longer has a well-defined low level circulation. Instead, this disturbance has a long oval area of circulation extending across 10 degrees of longitude, from about 33W to 43W, as seen in a QuikSCAT satellite pass from 4:11am EDT this morning. The heaviest thunderstorm activity has shifted eastward several hundred miles since last night, from 40W to about 35W. It appears that if this disturbance develops, it will happen from this more easterly position. The model runs from last night and this morning (Figure 3) all used the more westerly position of 40W, so can be disregarded. The system is moving slowly west at 10 mph, and could be near or north of the Lesser Antilles Islands on Thursday. Wind shear over the system is low, 5-10 knots, and the wave is over warm SSTs of 83-86F (28.5-30 C). Wind shear is forecast to remain low over the next few days, and the system has the potential to become a tropical depression by Monday. A modest inhibiting factor might be the large area of dry air and African dust to the wave's north.


Figure 3. Preliminary model tracks for Invest 98L. These models are described at the NHC web site.

New wave coming off the coast of Africa
A strong new tropical wave is emerging from the coast of Africa today near the Cape Verde Islands. Some of the computer models continue to develop this wave into a tropical storm or hurricane by the middle of next week.

Which of these three waves should most concern us? Both the wave coming off Africa today and the one in the middle of the Atlantic--98L--will probably end up recurving out to sea. However, 99L is already in the Caribbean and is forecast to enter a low shear environment, so this is the one to be most concerned with.

Dr. Gray's September 1 forecast
The hurricane forecast team at Colorado State University headed by Phil Klotzback and Dr. Bill Gray issued their September forecast for Atlantic hurricane activity today. They predict 5 named storms, 3 hurricanes, and 2 intense hurricanes for September, which is about normal for that month. They predict an additional 2 named storms and one hurricane in October, and one named storm in November. This would give the hurricane season of 2006 total of 13 named storms, 5 hurricanes, and 2 intense hurricanes. An average season has 11 named storms and 6 hurricanes. They credited dry air from the Sahara and more El Nino-like conditions than expected for the lower than average hurricane activity observed in August. Prices of oil, natural gas, and heating oil futures fell on commodity markets by 1-3% on the news of the forecast. The Klotzbach/Gray team originally forecast that 17 named storms would form this year.

Typhoon Ioke
Typhoon Ioke is now not even a Category 4 storm, having weakened a to mere strong Category 3 typhoon with 125 mph winds. It still has a chance to re-strengthen to a Category 4 in the next few days, before increasing wind shear and cooler waters will permanently take it out of Category 4 territory.

Next update
I'll have an update Sunday morning, unless there's some major development today to report.

Jeff Masters

Updated: 2:44 PM GMT en Septiembre 02, 2006

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John bears down on Baja; new threat in the Atlantic; new Dr. Gray forecast

By: JeffMasters, 8:13 PM GMT en Septiembre 01, 2006

Hurricane John is hours away from a strike on the southern tip of Baja as a borderline Category 2 or 3 hurricane. The Air Force Hurricane Hunters found a central pressure of 958 mb, and top winds of 110 mph at the surface at about 10am PDT. John is expected to maintain this intensity up until landfall. John is a very small hurricane, and the exact point of landfall will make a critical difference on how much damage the storm does. A 50-mile wide section of the coast will experience hurricane force winds. Satellite animations of John's current track suggest it will move up the relatively sparsely populated east side of the Baja Peninsula, sparing the resort towns of Cabo San Lucas and San Jose del Cabo the worst of the eyewall's winds. Radar from Cabo is most impressive!


Figure 1. Visible satellite image of Hurricane John from 1:45pm EDT Friday 9/1/06. Tropical Storm Kristy is also visible. Image credit: NOAA Visualization Laboratory.

Given the small size of the hurricane, the impact on Baja is likely to severely disrupt the storm. A much weakened John should continue north along Baja, dumping copious amounts of rain along the way. John's rains may make it all the way to San Diego, but it would be a major surprise if the storm were a tropical depression by then.

NHC declares a new "invest" on African tropical wave
A tropical wave near 11N 39W, midway between Africa and the Lesser Antilles Islands, has developed a well-defined low level circulation today. There has been a moderate increase in the thunderstorm activity associated with this wave, and the NHC has just designated this wave as Invest 98L. The system is moving west at 10-15 mph, and is expected to be near the Lesser Antilles Islands Wednesday. Wind shear over the system is low, 5-10 knots, and the wave is over warm SSTs of 83-86F (28.5-30 C). Wind shear is forecast to remain low over the next few days, and the system has the potential to become a tropical depression by Sunday. The main inhibiting factor would seem to be the large area of dry air and African dust to the wave's north (have we heard that refrain before this season?) The SHIPS intensity model is very aggressive with this system, intensifying it to a hurricane by Tuesday. That's not going to happen, it takes a lot longer than that for disturbance to organize into a hurricane.


Figure 2. Preliminary model tracks for Invest 98L. These models are described at the NHC web site.

Dr. Gray's September 1 forecast
The hurricane forecast team at Colorado State University headed by Phil Klotzback and Dr. Bill Gray issued their September forecast for Atlantic hurricane activity today. They predict 5 named storms, 3 hurricanes, and 2 intense hurricanes for September, which is about normal for that month. They predict an additional 2 named storms and one hurricane in October, and one named storm in November. This would give the hurricane season of 2006 total of 13 named storms, 5 hurricanes, and 2 intense hurricanes. An average season has 11 named storms and 6 hurricanes. They credited dry air from the Sahara and more El Nino-like conditions than expected for the lower than average hurricane activity observed in August. Prices of oil, natural gas, and heating oil futures fell on commodity markets by 1-3% on the news of the forecast. The Klotzbach/Gray team originally forecast that 17 named storms would form this year.

Ernesto
Ernesto, now a tropical depression, has dumped up to a foot of rain on North Carolina and Virginia. I'll have a summary of some lessons learned from tracking the storm in tomorrow's blog.

Typhoon Ioke
Typhoon Ioke is no longer a super typhoon, having fallen below the 150 mph winds threshold for that designation. It is, however, still a Category 4 storm with 135 mph winds, and may stay a Cat 4 for three more days. However, its amazingly long run as an intense typhoon appear numbered--it's getting far enough north that a trough of low pressure should be able to grab it by Tuesday, weaken it, and pull it northwest towards Japan.

Some impressive satellite loops and 3-D images of Ioke passing Wake Island are available at the RTS Weather Station on Kwajelein Atoll.

Another wave to keep an eye on
The tropical wave near 16N 55W is surrounded by a large cloud of dry air and African dust, but has slowly been able to pump more moisture into its center each night over the past few days as thunderstorm development kicks up then dies away. The thunderstorm activity surrounding the wave has died away again this afternoon, but will probably pick up again tonight, during the normal nighttime peak in thunderstorm activity over the oceans. By Sunday, the wave may have enough moisture to develop. It should be in the Lesser Antilles Islands at that time.

Next update
I'll have an update Saturday morning.

Jeff Masters

Updated: 11:28 PM GMT en Septiembre 01, 2006

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Ernesto storms ashore; John bears down on Baja

By: JeffMasters, 2:15 PM GMT en Septiembre 01, 2006

Tropical Storm Ernesto slammed ashore at 11:30pm EDT last night near Cape Fear (Wilmington) North Carolina. Just prior to landfall, the Hurricane Hunters observed a partial eyewall with 70 mph surface winds, but Ernesto never made it to hurricane strength. Ernesto has brought heavy rain to North Carolina--up to a foot in some areas--and an extensive area of 6-8 inches (Figure 1). Three tornadoes were reported in North Carolina yesterday. One of them damaged the roof of a home near Morehead City. Up to 1500 families needed to be evacuated from low-lying areas in the state due to river flooding. However, no major damage has been reported, and Ernesto's storm surge was only 1-3 feet where it came ashore near Cape Fear. Cape Fear reported 70 mph wind gusts last night as the center crossed land (Figure 2). We've archived a nice 3-hour radar animation of the storm making landfall in North Carolina.

Ernesto will remain a tropical storm today, then make the transition to an extratropical storm on Saturday. Lots of people's Labor Day weekend plans are going to be spoiled by the copious rains that will spread up the East Coast and into the Great Lakes. However, large portions of North Carolina, Maryland, Virginia, and Delaware are under drought conditions, so Ernesto's rains will be welcome for some.


Figure 1. Total precipitation from Ernesto estimated by the Morehead City radar before it failed.


Figure 2. Wind analysis of Ernesto at landfall in Cape Fear, NC at 12:30am EDT 9/1/06. Only a small area of 50 knot (58 mph) winds (green area) affected the coast.

Hurricane John
Hurricane John has re-intensified into a dangerous Category 3 hurricane, and is headed for a landfall on the tip of Mexico's Baja Peninsula about 3pm PDT today. John's appearance on satellite imagery this morning is impressive, with a well formed eye and good upper-level outflow on all sides. The storm should be able to maintain Category 3 intensity up until its landfall on the Baja. The Air Force Hurricane Hunters are on their way to the storm now to provide last minute intensity measurements of the storm.

John is a threat to the U.S.
In a previous blog, I discussed in detail the historical record of the five Eastern Pacific tropical cyclones that have affected the U.S. with tropical storm force winds. Three of the four main global forecast models now bring John or its remnants northward to San Diego by Labor Day. In particular, the reliable GFDL model has John as a 40-mph tropical storm Monday afternoon near the Mexico/California border. There is still the possibility that John will get forced westward, but residents all along the Baja Peninsula should be prepared for John to bring heavy rains and high winds their way. The exact strength of the storm during this trek will depend heavily on how close the eye passes to Baja today; a direct hit on the tip of Baja will severely disrupt the storm, but a sideswipe may leave the storm strong enough to bring hurricane and tropical storm conditions unusually far north along the Baja Peninsula. I give John a 10% chance of bringing sustained winds of tropical storm force to San Diego.

Super Typhoon Ioke
Super Typhoon Ioke continues to churn in the Central Pacific as a Category 4 storm with 150 mph winds, and it expected to stay a Cat 4 or 5 for at least three more days. However, its amazingly long run as an intense typhoon appear numbered--its getting far enough north that a trough of low pressure should be able to grab it by Tuesday, weaken it, and pull it northwest towards Japan.

Some impressive satellite loops and 3-D images of Ioke passing Wake Island are available at the RTS Weather Station on Kwajelein Atoll.

African tropical waves
The tropical wave near 16N 54W is surrounded by a large cloud of dry air and African dust, but has slowly been able to pump more moisture into its center each night over the past few days as thunderstorm development kicks up then dies away. By Sunday, the wave may have enough moisture to develop. It should be in the Lesser Antilles Islands at that time.

A tropical wave near 12N 38W, midway between Africa and the Lesser Antilles Islands, has changed little since yesterday. Some slow development of this system is possible over the next few days.

Next update
I'll have an update late this afternoon as Hurricane John approaches Baja.

Jeff Masters

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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