Dr. Jeff Masters' WunderBlog

Busy Times in the Tropics This Week!...continued

By: JeffMasters, 2:10 AM GMT en Agosto 01, 2007

Guest blogger Margie Kieper


Tuesday evening update: Well, 36 hours have passed since Monday morning, and Usagi does indeed look impressive. JTWC has upgraded the intensity to 120 kt and the eye continues to clear out:

Usagi vis


With ocean heat content diminishing from here on, it's hard to see how Usagi can intensify more, but JTWC has forecast a super typhoon (130 kt).

TD-Eight was upgraded to TS Erick, with this charmer from Lixion Avila, "DVORAK T-NUMBERS AT 0000 UTC FROM BOTH TAFB AND SAB INSIST THAT THE SYSTEM IS A TROPICAL STORM."

* * * * * * *

Tuesday lunchtime update: Because of a busy workload and a sick kitty (Squeak; aka Furball, Metcat), updates today will be minimal, but I'll update with satellite imagery tonight. If you have questions, email them to viewfromthesurface at gmail...and I'll answer them, if I'm able.

The Pacific Ocean is on a roll today.

Invest 99E is continuing to look good this morning, and is likely a TD by now. Update: was designated TD-Eight this afternoon.

Usagi's appearance on satellite continues to improve on IR and water vapor imagery, and the underlying structure continues to improve as well, as this latest of 37gHz microwave images shows, and can be compared with the two others posted earlier in this blog entry:

Usagi 37gHz


Usagi's intensity has been increased to 115 kt by JTWC (1-minute max surface windspeed) and 80 kt (10-min wind) by JMA, and it is close to it's maximum intensity, as ocean heat content will steadily lower, between now and landfall in Japan, which should have an impact regardless of the excellent outflow. At the moment, Usagi is a very powerful typhoon.

Regards all the angst on the blog comments yesterday on 99L: Most important is that you will never hear hype from me when blogging about tropical disturbances. Seeing the ocean of dry air ahead of 99L, it was not difficult to have an idea about what was going to happen. Here's something to note: that area just off the South American coast is a kind of a sweet spot. There is always good divergence flowing north that, while it may resemble outflow, is not necessarily indicative of an increase in vorticity. The low level winds are just so, to support a developing low, moisture is drawn from the ITCZ...but many lows associated with a tropical wave that look good there, will fade afterwards when gaining latitude and leaving those conditions behind, especially if moving into a more hostile environment.

It appears the surface circulation of the low associated with Invest 99L opened up or elongated this morning, both on satellite imagery and looking at the earlier QuikSCAT. The dry air is preventing moisture from the ITCZ from making it to the disturbance as it gains latitude, and so it is losing definition. The tropical wave may find a better environment by the time it moves into the western Caribbean or into the East Pacific.


Tuesday morning update: Usagi in the West Pacific continues to steadily strengthen and improve in structure. This morning the eye cleared out, and most recently the structure of the core has become more symmetric. Usagi has been a large, rather sloppy-looking tropical cyclone overall, but don't be fooled by this appearance. As I mentioned yesterday morning, this typhoon should be looking fairly impressive by 00Z 1 August, in about nine hours from this post. Here is a microwave from earlier this morning showing consolidation in the center and continued banding of convection around the center:

Usagi 37gHz


There are two other areas being monitored in the West Pacific for possible development.

* * * * * * *

In the North Atlantic, as predicted by NHC yesterday, TD-Three has strengthened into Chantal, and strengthening has continued, tilted but clearly tropical, moving rapidly northeast and being pulled into the strong trough coming off the East Coast, spinning furiously like a biker pedaling downhill, on its way to extratropical transition. Life in the fast lane.

Invest 99L underwent a little reorganziation overnight and the mid-level circulation redeveloped in early morning, along with some banding structure. Convection continues to have a hard time sticking due to the dry air, but the low level organization is still intact, so there is some potential to develop into a tropical depression over the next day or so -- but as I said yesterday, chances are that nothing is going to come of this over the next day or so.

More recent morning imagery shows the low level circulation is becoming a little looser, as convection cannot be maintained. It appears this will fall apart as the day progresses.

Finally, there looks to be some potential for development - really, more potential than 99L, as there is quite a lot of energy in this area of disturbed weather - at the tail of the trough coming off the East Coast, east of Georgia and the Carolinas -- but again, a fish spinner.

In the East Pacific, Invest 99E has developed some convection to the southwest of the low level circulation, so that it is no longer an exposed "swirly." A microwave pass from this morning covered enough of the area to show the banding convection and a solid low level structure, so expect this to have potential to develop into a tropical depression as it heads out into the Pacific. Recent visual imagery shows good outflow has started to develop.

* * * * * * *

Monday evening update: Convection was able to reform over the center of the exposed low level center of invest 98L tonight, and it has become TD-Three, very near tropical storm strength. It is now centered well north of Bermuda and tracking northeast towards the tip of Newfoundland. The satellite floater is positioned so that the low off the SE coastline can also be observed for development, while TD-Three is rapidly moving north out of the image frame.

Earlier this evening, easterly shear pushed the mid-level circulation and convection right off of the low level center of invest 99L, where it spun off to the west and evaporated, as the low level center continued to move to the northwest, a process that was captured very clearly on the satellite imagery, as seen here on an IR from the NRL web site -- the gray scale helps to determine the height of the clouds:

99L sheared


As I mentioned earlier today, 99L is headed for a large area of dry air. This can be seen on the IR satellite imagery (here, RGB), which I've marked to show the successive surges of the Saharan Air Layer (SAL).

99L and SAL


Here a water vapor image clearly shows the extent of the dry air across the Atlantic and eastern Caribbean.

99L and dry air


In the West Pacific, Usagi has been steadily strengthening and the eye is starting to become visible on IR and VIS imagery. A microwave from this afternoon shows the solid inner ring of the low level circulation surrounding the eye, partially banded by strong convection (pink).

Usagi 37gHz


* * * * * * *

Monday Afternoon update: The very nice tropical wave that moved off Africa last Thursday, that is now located at about 50W, has developed rotation and convection and has been designated invest 99L by NHC. While the most recent surge of SAL only extends out to about 40W, most of the tropical North Atlantic and eastern Caribbean remain very dry, so once this wave moves out of the ITCZ and into the eastern Caribbean, chances are that nothing is going to come of it for the next two or three days. The vis loop already shows convection on the northeast and northwest side of the disturbance dissolving as it moves into the dry air.

Convection momentarily burst near the center of 98L, well north of Bermuda and on its way to the middle of the North Atlantic, before getting sheared by the upper level flow.

More on Usagi tonight.

Don't try to adjust that dial: Yes, it does appear that over the past week the NRL TC website has been quietly going berserk. Dalila is done, but keeps coming and going, as do various invests intermittently labeled "Lima" or "Bilis." One could say the site is suffering from Bilis-Lima-ia.

* * * * * * *

For Jeffs early August hurricane outlook, which came out Sunday, link here.

Updated: 4:21 AM GMT en Agosto 01, 2007

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Busy Times in the Tropics This Week!

By: JeffMasters, 4:15 PM GMT en Julio 31, 2007

Guest blogger Margie Kieper


Tuesday lunchtime update: Because of a busy workload and a sick kitty (Squeak; aka Furball, Metcat), updates today will be minimal, but I'll update with satellite imagery tonight. If you have questions, email them to viewfromthesurface at gmail...and I'll answer them, if I'm able.

The Pacific Ocean is on a roll today.

Invest 99E is continuing to look good this morning, and is likely a TD by now. Update: was designated TD-Eight this afternoon.

Usagi's appearance on satellite continues to improve on IR and water vapor imagery, and the underlying structure continues to improve as well, as this latest of 37gHz microwave images shows, and can be compared with the two others posted earlier in this blog entry:

Usagi 37gHz


Usagi's intensity has been increased to 115 kt by JTWC (1-minute max surface windspeed) and 80 kt (10-min wind) by JMA, and it is close to it's maximum intensity, as ocean heat content will steadily lower, between now and landfall in Japan, which should have an impact regardless of the excellent outflow. At the moment, Usagi is a very powerful typhoon.

Regards all the angst on the blog comments yesterday on 99L: Most important is that you will never hear hype from me when blogging about tropical disturbances. Seeing the ocean of dry air ahead of 99L, it was not difficult to have an idea about what was going to happen. Here's something to note: that area just off the South American coast is a kind of a sweet spot. There is always good divergence flowing north that, while it may resemble outflow, is not necessarily indicative of an increase in vorticity. The low level winds are just so, to support a developing low, moisture is drawn from the ITCZ...but many lows associated with a tropical wave that look good there, will fade afterwards when gaining latitude and leaving those conditions behind, especially if moving into a more hostile environment.

It appears the surface circulation of the low associated with Invest 99L opened up or elongated this morning, both on satellite imagery and looking at the earlier QuikSCAT. The dry air is preventing moisture from the ITCZ from making it to the disturbance as it gains latitude, and so it is losing definition. The tropical wave may find a better environment by the time it moves into the western Caribbean or into the East Pacific.


Tuesday morning update: Usagi in the West Pacific continues to steadily strengthen and improve in structure. This morning the eye cleared out, and most recently the structure of the core has become more symmetric. Usagi has been a large, rather sloppy-looking tropical cyclone overall, but don't be fooled by this appearance. As I mentioned yesterday morning, this typhoon should be looking fairly impressive by 00Z 1 August, in about nine hours from this post. Here is a microwave from earlier this morning showing consolidation in the center and continued banding of convection around the center:

Usagi 37gHz


There are two other areas being monitored in the West Pacific for possible development.

* * * * * * *

In the North Atlantic, as predicted by NHC yesterday, TD-Three has strengthened into Chantal, and strengthening has continued, tilted but clearly tropical, moving rapidly northeast and being pulled into the strong trough coming off the East Coast, spinning furiously like a biker pedaling downhill, on its way to extratropical transition. Life in the fast lane.

Invest 99L underwent a little reorganziation overnight and the mid-level circulation redeveloped in early morning, along with some banding structure. Convection continues to have a hard time sticking due to the dry air, but the low level organization is still intact, so there is some potential to develop into a tropical depression over the next day or so -- but as I said yesterday, chances are that nothing is going to come of this over the next day or so.

More recent morning imagery shows the low level circulation is becoming a little looser, as convection cannot be maintained. It appears this will fall apart as the day progresses.

Finally, there looks to be some potential for development - really, more potential than 99L, as there is quite a lot of energy in this area of disturbed weather - at the tail of the trough coming off the East Coast, east of Georgia and the Carolinas -- but again, a fish spinner.

In the East Pacific, Invest 99E has developed some convection to the southwest of the low level circulation, so that it is no longer an exposed "swirly." A microwave pass from this morning covered enough of the area to show the banding convection and a solid low level structure, so expect this to have potential to develop into a tropical depression as it heads out into the Pacific. Recent visual imagery shows good outflow has started to develop.

* * * * * * *

Monday evening update: Convection was able to reform over the center of the exposed low level center of invest 98L tonight, and it has become TD-Three, very near tropical storm strength. It is now centered well north of Bermuda and tracking northeast towards the tip of Newfoundland. The satellite floater is positioned so that the low off the SE coastline can also be observed for development, while TD-Three is rapidly moving north out of the image frame.

Earlier this evening, easterly shear pushed the mid-level circulation and convection right off of the low level center of invest 99L, where it spun off to the west and evaporated, as the low level center continued to move to the northwest, a process that was captured very clearly on the satellite imagery, as seen here on an IR from the NRL web site -- the gray scale helps to determine the height of the clouds:

99L sheared


As I mentioned earlier today, 99L is headed for a large area of dry air. This can be seen on the IR satellite imagery (here, RGB), which I've marked to show the successive surges of the Saharan Air Layer (SAL).

99L and SAL


Here a water vapor image clearly shows the extent of the dry air across the Atlantic and eastern Caribbean.

99L and dry air


In the West Pacific, Usagi has been steadily strengthening and the eye is starting to become visible on IR and VIS imagery. A microwave from this afternoon shows the solid inner ring of the low level circulation surrounding the eye, partially banded by strong convection (pink).

Usagi 37gHz


* * * * * * *

Monday Afternoon update: The very nice tropical wave that moved off Africa last Thursday, that is now located at about 50W, has developed rotation and convection and has been designated invest 99L by NHC. While the most recent surge of SAL only extends out to about 40W, most of the tropical North Atlantic and eastern Caribbean remain very dry, so once this wave moves out of the ITCZ and into the eastern Caribbean, chances are that nothing is going to come of it for the next two or three days. The vis loop already shows convection on the northeast and northwest side of the disturbance dissolving as it moves into the dry air.

Convection momentarily burst near the center of 98L, well north of Bermuda and on its way to the middle of the North Atlantic, before getting sheared by the upper level flow.

More on Usagi tonight.

Don't try to adjust that dial: Yes, it does appear that over the past week the NRL TC website has been quietly going berserk. Dalila is done, but keeps coming and going, as do various invests intermittently labeled "Lima" or "Bilis." One could say the site is suffering from Bilis-Lima-ia.

* * * * * * *

For Jeffs early August hurricane outlook, which came out Sunday, link here.

Updated: 9:07 PM GMT en Julio 31, 2007

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im in ur blogz, dishin ur TC storyz *

By: JeffMasters, 1:34 PM GMT en Julio 30, 2007

Guest blogger Margie Kieper

* lolcats, for the uninitiated and my own contribution to the genre: metcat.


As Bob King sympathized with me a couple of weeks ago, "The only thing worse than blogging is not blogging." And what better way to have your cake and eat it too, than to blogbut not blog. So, after doing my part to help save the Shire and its furry-footed forecasters from Mordor: I'm back.

But what TC storyz havent already been addressed ad nauseam? The collective ennui of the lingering ENSO-neutral state of the equatorial East Pacific, the ongoing SAL in the East Atlantic, and anticipating the predictable seasonal predictions of what may lie in-between (an active / busy / above-normal season), is almost enough to impede lifting fingers to keyboard.

Almost.

For those of you who have recovered from the 2005/2006 very public debate regarding hurricanes and global warming, you can pick it up again as the next chapter rolls out today (and why not, since youve all finished that last Harry Potter). An extraordinarily large number of news media were advanced a preview of a paper due to clear the publication embargo today, providing a new twist on analysis of North Atlantic tropical cyclone activity in relation to SST, and it seems all of them carried a story on it. Most tout a sensational headline about global warming increasing hurricanes, but I like this one, Tropical storms stepping up with climate change, because it appears they actually did read the paper.

Theres sure to be some ripples in the pond, so grab the popcorn and Google News (or whatever your poison) this week to catch the dizzying repartee which might be a lot more palatable if it were limited to pirate talk (arrr!).

Another news trend cropped up the last part of July: fearful the public might forget about the danger of hurricanes making landfall during the hurricane season, rather than just remind us regularly during the off-season, its now become vogue to remind us periodically during the season. So, for anyone who hasnt yet heard this several times recently: a slow July is normal, and doesnt mean were not in for an active season. August starts the day after tomorrow, and its going to be active. Or busier than average. Or above normal. Maybe not as many storms as predicted in May, but still more than normal. Certainly more than the old normal. Possibly more than the post-1994 normal. July to August, as far as hurricanes are concerned is, apparently, like getting in a car with your grandmother behind the wheel, put-putting along slowly in the right lane, then, just as youre about to doze off, suddenly realizing that shes put on some pre-1930s-trendy aviator goggles, is laughing maniacally, and youve swerved into the fast lane, in some crazy freewheeling Fear-and-Loathing road trip.

Im not sure how far this trend can go, but it is conceivable that well be reminded weekly, should any week in August, September, or October go by without a hurricane, that this is an active season. For those of you who want to anticipate how active, tune in to CSU on August 3rd and NOAA on August 9th.

Of course, if you want to know now, you can trust the real hurricane experts from Tulsa, OK:

Tropical developments suggest a hurricane may come ''very near the East Coast of Florida early in the 11- to 15-day period,'' Stephen Strum, president of Frontier Weather Inc. in Tulsa, Okla., said in a report.
Should someone let them know how accurate the models - er, "tropical developments" - are, two weeks out?...Nah!

Theres an invest in the North Atlantic not worth mentioning unless you planned to golf today in Bermuda which may get a tad more interesting once it is completely ocean-bound and of hardly any interest to anyone.

While there is constant talk about tropical cyclone activity in the North Atlantic, there is tropical cyclone activity in other basins of the world this week.

The West Pacific has come alive after a late start, with super-typhoon Man-yi in mid-July. Japan is currently in the cross-hairs for Typhoon Usagi, which developed a good underlying structure this weekend (oh, the anticipation of the next decent 37gHz pass!) and will likely be looking impressive 36 hours from now (00Z 1 August). When it does, I'll be keeping you up to date with interesting imagery and news from that part of the globe.

The 2007-2008 Southwest Indian Ocean season has started early with two invests in the neighborhood of Diego Garcia, one of which developed into a short-lived tropical storm.

Finally, borrowing another page from Brendan's book: That Which It Is No Longer Necessary To Blog About is behind us (and, hopefully as well, Maxs days of jokingly referring to me as Agatha). So, I wont be mentioning that either. :)

However, it is a good time to mention that Max has recently started his own hurricane blog, over at Miamis WPLG Local 10, which immediately jumped to the top of my blog roll. A word of warning, Max: the only thing worse than blogging is not blogging.

* * * * * * *

For Jeffs early August hurricane outlook, which came out Sunday, link here.

Updated: 4:15 PM GMT en Julio 31, 2007

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Early August hurricane outlook

By: JeffMasters, 2:12 PM GMT en Julio 29, 2007

A tropical disturbance (98L) a few hundred miles north of the central Bahamas has become only a little better organized since yesterday. Heavy thunderstorm activity has increased, and the beginnings of some upper-level outflow to the northeast is apparent on visible satellite loops. A QuikSCAT satellite pass from 6:38am this morning revealed that 98L is attempting to form a closed circulation at the surface, and had top winds of at least 25 mph.

Water vapor satellite loops show an upper-level low pressure system to 98L's northeast, and this upper low is bringing about 15 knots of wind shear over the disturbance. The GFS and GFDL models predict that the upper low will move north-northeast in tandem with the disturbance, keeping low enough shear over it that a tropical depression could form. The other reliable models do not develop 98L. At present, it appears that Bermuda is the only place that needs to concern itself with 98L. SSTs are warm enough to support tropical storm formation until 98L reaches a point 500 miles or so north of Bermuda. The Air Force Hurricane Hunter aircraft scheduled to investigate 98L this afternoon was canceled, and no new flights are planned.


Figure 1. Preliminary model tracks for 98L.

Early August hurricane outlook
In the first half of August, Atlantic tropical cyclone activity starts to pick up. Since the current active hurricane period began in 1995, eight of 12 years have had one or more named storms form during the first half of August, including the last seven years in row. The fact that we've had a quiet July does not mean we can expect a slower than average hurricane season. To illustrate, consider 2004--the first storm, Alex, did not get named until August 1, yet that season had 15 named storms, 9 hurricanes, and 6 intense hurricanes. Five named storms formed in first half of August of 2004. One item of comfort, though, is the fact that 2007 is definitely not a repeat of 2005--we were already up to "G" in the alphabet at this point in 2005.


Figure 2. Historical Atlantic hurricane and tropical storm activity, 1851-present. Figure modified from NOAA's original.

As seen in Figure 2, hurricane activity does take a bit of an upward jump around August 1, but the real action doesn't start until August 18. It should not surprise us, then if we go a few more weeks without a named storm. I am still expecting an above-average hurricane season with 12-14 named storms (10-12 more, since we've already had two), with at least one major hurricane hitting the U.S. However, the decline in SSTs relative to normal over the past two months means we should have a less active season than originally thought. I'm guessing that the Dr. Bill Gray/Phil Klotzbach August forecast, due to be released Friday August 3, will have two fewer named storms compared to their May 31 forecast.


Figure 3. Tracks of all tropical storms and hurricanes since 1851 that formed August 1-15.

Sea Surface Temperatures
Early August storms can occur anywhere, and strike anywhere (Figure 3), since the oceans have finally heated up to the point where the entire tropical Atlantic can support hurricane formation. Sea Surface Temperature (SSTs) remained near average over the tropical Atlantic between Africa and the Lesser Antilles in July (Figure 4), thanks to plenty of African dust keeping sunlight from heating up the ocean. A stronger than average Bermuda High has also helped cool the ocean more than normal, thanks to the faster trade winds it brought over the ocean in June and July. However, SSTs are 0.5-1.0 C above average over much of the Caribbean and Gulf of Mexico, so there is still good reason to expect an above-average number of tropical storms and intense hurricanes this hurricane season. The total amount of heat energy in the upper layer of the ocean (the Tropical Cyclone Heat Potential, TCHP) remains high in the Western Caribbean--near the record levels observed in 2005. However, TCHP is much lower over the rest of the tropical Atlantic, including the Gulf of Mexico.


Figure 4. Sea Surface Temperature (SST) departure from average for July 26, 2007. Image credit: NOAA.

Wind shear
Wind shear has been near normal, averaged over the tropical Atlantic during July. Wind shear is predicted to be near or below normal for the first half of August.

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa. By early August, dust activity typically diminishes, but it is not well-understood how to forecast these dust outbreaks. We have seen a decline in the amount of dust over the past week, as one might expect from climatology. Since the long-range GFS forecast does not show any major changes to the weather pattern over Africa the next two weeks, I am expecting African dust activity to remain near normal through mid-August.

Steering currents
The hurricane steering pattern for the next two weeks should be near normal, with no areas at above-average risk for a hurricane strike. I discussed this in detail in Friday's blog. Steering current patterns are not predictable more than about two weeks in advance, and there is no way to tell if this steering current pattern will remain in place past mid-August.

Summary
Recent history suggests a 75% chance of at least one named storm occurring in the first half of August. I'll go with climatology and forecast a 75% chance this year, as well, since SSTs, wind shear, and African dust/dry air should all be near normal. With the steering current patterns expected to be near normal, no areas can be singled out as being at higher risk than average. We'll have to keep a careful eye out late this week, when a cold front is expected to sweep off the East Coast of the U.S. Several of the models are indicating the possibility that a tropical depression could form at the tail end of the cold front by Thursday or Friday. This would most likely happen off the Carolina coast, but could also occur in the Northeastern Gulf of Mexico, near the Florida Panhandle. I think it is still too early to get a tropical storm forming between Africa and the Lesser Antilles Islands this week, but next week we could see something.

Last blog for a week
This will be my final blog until Monday, August 5, as I am taking a week's vacation to do some camping and paddling along Lake Huron's gorgeous Georgian Bay. I've arranged for an able substitute blogger to make daily posts here this week, but I will be able to do some blogging beginning Friday if something nasty pops up.

Jeff Masters

Updated: 4:09 PM GMT en Julio 29, 2007

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Disturbance 98L forms north of the southern Bahamas

By: JeffMasters, 2:18 PM GMT en Julio 28, 2007

A concentrated area of thunderstorms has developed just north of the southern Bahamas Islands this morning, in association with a broad surface trough of low pressure. The NHC labeled this disturbance "98L" this morning, and the preliminary computer model tracks have the system moving slowly to the north-northeast. An upper-level low pressure system to 98L's northeast is bringing about 15 knots of wind shear over the disturbance. The GFS model predicts that the upper low will move north-northeast in tandem with the disturbance, keeping low enough shear over it that a tropical depression could form. The other reliable models do not develop 98L. At present, it appears that Bermuda is the only place that needs to concern itself with 98L. An Air Force Hurricane Hunter aircraft is scheduled to investigate the storm Sunday afternoon.


Figure 1. Preliminary model tracks for 98L.

Jeff Masters

Updated: 5:52 PM GMT en Julio 28, 2007

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Steering current forecast

By: JeffMasters, 1:25 PM GMT en Julio 27, 2007

Thunderstorm activity in association with a westward-moving tropical wave has decreased over the Northwest Gulf of Mexico this morning. Wind shear is 15-20 knots over the wave, and is expected to remain at least 15 knots over the next two days. This is probably too high to allow tropical development to occur. Wind shear is also expected to be 20 knots or higher over the Caribbean for the next week, which should stifle any development there.

Two computer models, the GFS and ECMWF, develop a tropical storm off the coast of Africa by Monday. The African wave that would likely be the seed for this moved off the coast last night, but looks unimpressive this morning. Wind shear is 30 knots over the wave and the surrounding region of the Intertropical Convergence Zone (ITCZ), and is forecast to remain high in this region for several days. Any tropical storm development will probably have to wait until the wave gets at least 1000 miles from the coast. The Saharan Air Layer (SAL) is relatively weak and far to the north at present, so dry air and Saharan dust should not be a major impediment. The UKMET and NOPGAPS models do not develop anything over the coming week, and predict high wind shear over the region. My best guess is that the earliest we would see a tropical storm form between Africa and the Lesser Antilles would be Thursday August 2nd.

Steering current forecast
The hurricane steering pattern for the next two weeks over the North Atlantic should be near normal, with no areas at above-average risk for a hurricane strike. The tool I like to use to study steering currents is the 500 millibar (mb) upper-air forecast from the latest run of the GFS model. Plotted on these maps are lines showing how high above sea level one finds a pressure of 500 mb. Where a U-shaped bend occurs, a trough of low pressure is present. Any tropical cyclones that get far enough north to "feel" the trough's presence will recurve to the north. Conversely, an upside-down "U" in the 500 mb height lines reveals the presence of a ridge of high pressure. Ridges force tropical cyclones to move westward (in the Northern Hemisphere.) As seen in Figure 1, a ridge of high pressure was present this morning over the U.S. East Coast, with troughs of low pressure over the mid-Atlantic and Great Lakes. Under this steering pattern, any hurricanes in the mid-Atlantic north of about 25 degrees latitude would be recurved by the mid-Atlantic trough, but storms closer to the U.S. would not get recurved until they came very close to the coast and began feeling the Great Lakes trough. One can pull up a loop going out a full 16 days of the 500 mb forecast and watch the evolution of the trough/ridge pattern to see how the steering currents might change.


Figure 1. GFS model forecast of heights of the 500 mb surface above sea level (white lines) for 8am EDT today. The colors show how much counter-clockwise spin is present (vorticity). High vorticity is associated with storms.

To get an idea of the uncertainty in these steering pattern forecasts, a good tool to use is the Global Ensemble Forecast System (GEFS) charts. The GEFS charts show runs of the GFS model done using 20 slightly different initial conditions. This creates an "ensemble" of 20 possible forecasts. By examining how these 20 different forecasts diverge with time, one can get an idea of how confident one should be of major changes forecast by the GFS model.

These 20 forecast solutions are plotted as a series of colored lines that trace out the height (in decameters, or tens of meters) above sea level where a certain pressure is found. It turns out that the southern edge of the jet stream is currently found at a 500 mb height of about 582 decameters (5820 meters). Go to the NOAA experimental model graphics web site, click on the latest "Charts" link for the GEFS model, then select to plot up the "500mb 540/582 Hgt Contours". The loop takes a while to load, but gives one the best idea of how the steering currents might evolve. The 20 forecasts all lie close to each other the first few days of the forecast, then begin to diverge at later times. By the end of two weeks, you'll see why these are called "spaghetti plots" (Figure 2).



Figure 2. Forecast of the location where the 500 mb pressure surface will be at a height of 582 decameters (5280 meters) above sea level. This height marks the approximate southern boundary of the jet stream. Top image: the forecast for 8am EDT today. Bottom map: the forecast for 26 days from now. The 20 different lines correspond to 20 different runs of the GFS model with slightly different initial conditions. The runs were all initialized at 06 GMT (8am EDT) July 27. Image credit: NOAA/NCEP.

For this morning's GEFS run, we see that 16 days from now most of the 20 ensemble members are predicting a shallow trough of low pressure over the Eastern U.S., similar to what we've seen through most of June and July this year, and during the entire 2006 hurricane season. However, the trough is forecast to be not as strong as we saw in 2006, and thus will be less likely to recurve storms approaching the U.S. This trough is also forecast to be transient--GEFS runs ever past week are pointing to a near-normal jet stream pattern over the coming two weeks, bringing an alternating series of weak ridges and troughs across North America and the Atlantic. This will bring a near normal chance of landfalling tropical cyclones to all regions of the Atlantic. This is in contrast to the steering pattern of 2006, which saw the jet stream get "stuck" in place, with a strong trough of low pressure over the Eastern U.S. most of the season.

My next update will be Sunday, unless there's some major development to talk about.
Jeff Masters

Updated: 1:32 PM GMT en Julio 27, 2007

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Tropical update; 4th warmest June on record

By: JeffMasters, 1:51 PM GMT en Julio 26, 2007

Thunderstorm activity has increased over the central Gulf of Mexico this morning, thanks to a tropical wave moving westward at 20-25 mph. Winds have increased to 20-25 mph at the Gulf of Mexico buoy 275 miles SSE of Sabine Pass, Texas, but pressures are not falling. Wind shear is 20 knots over the wave, and is expected to remain at least 20 knots over the next two days. This is probably too high to allow tropical development to occur.

Two computer models, the GFS and ECMWF, are indicating the possibility of a tropical storm forming in the mid-Atlantic between Africa and the Lesser Antilles Islands by August 1. This is still a bit early for something to form in this region, given that the SSTs are average there. However, there is a strong tropical wave about to emerge from the coast of Africa that may be something to watch early next week as it moves over the central Atlantic.

Fourth Warmest June on record
June 2007 was the fourth warmest June for the globe on record, and the period January - June of 2007 was the second warmest such period ever, according to statistics released by the National Climatic Data Center. The global temperature record goes back 128 years. The global average temperature for June was +0.55�C (+0.99�F) above the 20th century mean. Over land, June global temperatures were the third warmest ever measured. Ocean temperatures were a bit cooler (eighth warmest on record). All land areas, with the exception of Argentina, were warmer than average during the period January-June 2007.

June temperatures were particularly warm across Southeast Europe, where temperatures soared to 40�C (104�F). At least 40 deaths were blamed on the heat, and electricity demand reached record levels. Winter in the Southern Hemisphere was colder than average in Argentina and Australia, and Johannesburg, South Africa's largest city, received its first significant snowfall since 1981 on June 27.

23rd warmest June on record in the U.S.
In the U.S., June 2007 ranked as the 23rd warmest since record keeping began in 1895. The period January through May was the 18th warmest such period on record. It was the second driest January-June and driest April-June on record in the Southeast. Alabama was hardest hit, with 86 percent of the state's pasture and range lands in poor or very poor condition in early July.


Figure 1. Temperature departure from average for June 2007. Image credit: National Climatic Data Center.

Sea ice extent
Sea ice extent in the Arctic for June was the fourth lowest on record, the second straight month that we haven't had a record low. Arctic sea ice coverage in June has declined by about 10% since measurements began in 1979 (Figure 2).


Figure 2. Arctic sea ice extent for June, for the years 1979-2007. June 2007 had the fourth lowest Arctic sea ice extent since satellite measurements began in 1979. May sea ice coverage has declined about 10% since 1979. Image credit: National Snow and Ice Data Center.

I'll have a new blog Friday.
Jeff Masters

Climate Summaries

Updated: 10:27 PM GMT en Octubre 21, 2011

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Warmer Water, SUPER HURRICANES

By: JeffMasters, 12:33 PM GMT en Julio 24, 2007

The July 2007 issue of Scientific American has an article called "Warmer Oceans, Stronger Hurricanes" (referred to as "Warmer Water, SUPER HURRICANES" on the cover). The article is written by Dr. Kevin E. Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, and a lead author on the landmark 2007 climate report issued by the UN's Intergovernmental Panel on Climate Change (IPCC). The article makes the case that "evidence is mounting that global warming enhances a cyclone's damaging winds and flooding rains." The article presents some solid evidence to substantiate that point of view, which I will share below. However, I was disappointed in the general tone of the piece, which was over-hyped and did not paint an objective view of the current scientific thinking on the global warming/hurricane issue.

The hype
First off, the reader is hit with a dramatic full-page artist's depiction of the global super-hurricane of the future--a massive 5000-mile diameter Caribbean storm the size of North America. The storm's 200-mile eye is wider than the Florida Peninsula! Whoa, I said when looking at the whopper "SciAmicane". No doubt many readers perusing the magazine, trying to decide whether to buy it, had the same reaction and plunked down their $5 to read about this grim threat. OK, lets talk reality here. The largest tropical cyclone on record, Supertyphoon Tip of 1979, had a diameter of 1380 miles--less than one third the size of the SciAmicane. A storm like the SciAmicane cannot physically exist on Earth unless the oceans were to super-heat to about 122°F (50°C). Only an asteroid impact or similar calamity could create such a hypercane. Even the most extreme global warming scenarios do not heat the oceans to 122°, so the SciAmicane is there to sell magazines, not to illustrate what global warming might do to hurricanes.


Figure 1. Comparison of sizes: the Earth, the largest tropical cyclone on record (Supertyphoon Tip of 1979, 1380 miles in diameter), and the recently discovered hurricane-like vortex on Saturn (the Saturnicane). The "SciAmicane" is about the same size as the Saturnicane--5000 miles across.

The article also calls attention to 2004, when "an unprecedented four hurricanes hit Florida, and 10 typhoons made landfall in Japan". I've erroneously made this statement, too, but the truth is that Japan was hit by only four typhoons in 2004. Ten tropical cyclones that were of typhoon strength at some point during their life did hit, yes, but six of these had decayed to tropical storm or tropical depression strength by the time they hit Japan. The article then refers to a "consensus explanation" emerging to explain recent hurricane activity patterns, and "that explanation forebodes meteorological trouble over the long term." I'd say that the issue is still very much under dispute. In fact, the consensus statement on hurricanes and climate change adopted by the World Meteorological Organization in December 2006, in response to the recommendations of a panel of 125 hurricane researchers was thus: "Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point." Trenberth's article gives a list of four publications to read in the "more to explore" section, but none of these include the recent articles that call into question the strength of the global warming/stronger hurricane connection. (I apologize for not reviewing the many excellent articles that have appeared on this subject of late!)

The good science
There's quite a bit of good science in the article, which is worth reading if one keeps in mind its biases. In particular, I like the discussion of how global warming has affected precipitation and atmospheric water vapor. The 0.6°C (1.0°F) rise in Sea Surface Temperatures (SSTs) globally since 1970 has increased water vapor in the atmosphere by 4%, thanks to increased evaporation. This in turn has led to an 8% increase in global precipitation. Trenberth makes the point that no given hurricane can be blamed on global warming, but one can say 8% of a given storm's rainfall is due to global warming. There's also a nice discussion about how weaker than normal trade winds over the tropical Atlantic in 2005 caused less evaporational cooling than normal, allowing the ocean to heat to record temperatures. Finally, the conclusion of the article is one I certainly agree with:

We would all be wise to plan for more extreme hurricane threats.

Both theory and computer models predict a 3-5% increase in hurricane winds per degree C increase in tropical SSTs, and there is concern that the actual increase may be much more than this.

Jeff Masters

For a technical treatment of hypercanes, see Dr. Kerry Emanuel's paper, Hypercanes: a possible link in global extinction scenarios.

Climate Change

Updated: 8:03 PM GMT en Agosto 16, 2011

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Quiet Atlantic; police blow up weather station

By: JeffMasters, 2:34 PM GMT en Julio 23, 2007

There's not much to talk about in the Atlantic today. A tropical wave we were watching (97L), east of Bermuda, has moved north over colder waters and is no longer a threat to develop. A large area of Saharan dust and dry air is present between Africa and the Lesser Antilles Islands, which will discourage any development in this region over the next few days. Later in the week, the UKMET and ECMWF models are hinting that conditions may moisten enough for something to develop off the coast of Africa. However, tropical storm formation in this region is unusual in July, and I'd be surprised if something did develop.

The long range GFS model shows that the steering pattern for the next two weeks will be much different than what we saw in 2006 and so far in 2007. We will no longer have a dominant trough of low pressure over the Eastern U.S. that will act recurve storms out to sea. Instead, an alternating series of weak ridges and weak troughs rippling along the jet stream is expected. No particular region of the Atlantic will be at higher risk of being hit with such a pattern.

Police robot blows up weather station
If you've never seen one before, familiarize yourself with what a weather stations looks like. State Police in Virginia had apparently never seen one before, and sent a police robot in to blow up a "suspicious object" hanging from a tree near a hospital in Virginia. The object turned out to be a home weather station. A tree is not a very good place to put a weather station--how can you measure accurate precipitation and winds there? Perhaps that's what the police were wondering, too, and this made them suspicious enough to terminate the threatening weather station.

In case you missed it, here's my analysis of the QuikSCAT science presented at Thursday's Congressional hearing.

Jeff Masters

Updated: 2:36 PM GMT en Julio 23, 2007

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Bermuda tropical wave

By: JeffMasters, 4:13 PM GMT en Julio 22, 2007

A tropical wave near Bermuda (dubbed "97L" by NHC this evening) is interacting with an upper-level low pressure system just west of the island. The two weather systems are producing plenty of clouds and thunderstorms over a wide region of ocean. An area of concentrated thunderstorms has developed about 100 miles east of Bermuda, and we'll have to watch this area for continued development. Wind shear has decreased to about 10 knots over the area, and is expected to remain at 10 knots or less for the next two days, which is low enough to encourage development. However, the disturbance is moving northward towards cooler waters, and it will only have about 1 more day over favorable water temperatures greater than 80F. In any case, the system's expected northward track over the next three days means that any tropical storm that might develop will probably not last long or threaten any land areas. The Hurricane Hunter aircraft that was scheduled to investigate the system today was canceled, and no further flights are planned.

NHC's new Experimental Graphical Tropical Weather Outlook
Last week, NHC began issuing their new Experimental Graphical Tropical Weather Outlook. The product takes the standard Tropical Weather Outlook text and combines it with an infrared satellite image identifying the regions being discussed. It's similar to what I frequently do on my blogs, and I think NHC should make it a permanent feature on their web site. There's a feedback form on the web site to comment on the usefulness of the new product.



Figure 2. Infrared satellite image showing the upper level low interacting with a tropical wave near Bermuda (area 1). Image credit: NHC's new Experimental graphical Tropical Weather Outlook.

Jeff Masters

Updated: 11:33 AM GMT en Julio 23, 2007

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Tropical update

By: JeffMasters, 4:16 PM GMT en Julio 21, 2007

A tropical wave a few hundred miles north of Puerto Rico is moving into a region where an upper-level low pressure system is spinning. The two weather systems are producing plenty of clouds and thunderstorms over a wide region of ocean. Wind shear is about 20 knots over the area, so not much development today is expected. However, wind shear is expected to drop to about 15 knots Sunday in the area, which could allow some slow development. Water vapor satellite loops show that the tropical wave has brought copious moisture into the previously dry upper level low, and this low could gradually develop a surface low pressure area as thunderstorm activity continues to moisten the region. This system is currently stationary, but is expected to drift northwards over the next two days. A Hurricane Hunter aircraft is scheduled to investigate the area Sunday afternoon.


Figure 1. Water vapor image from this morning showing the upper level low that is sucking in moist air from a tropical wave.

Carolina low pressure system
Thunderstorm activity is starting to pick up off the Carolina coast waters, thanks to a cold front that has pushed off the coast. A regular extratropical low pressure system is expected to develop here today, an move northwards, bringing rain to New England on Monday. Due to high wind shear of about 30 knots and cool SSTs, this low is not expected to be tropical.

In case you missed it, here is my blog on the science of QuikSCAT that was presented at Thursday's Congressional hearing on NHC's turmoil.

OK, now you can go back to reading Harry Potter :-)

Jeff Masters

Updated: 4:19 PM GMT en Julio 21, 2007

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QuikSCAT science at yesterday's hearing

By: JeffMasters, 8:22 PM GMT en Julio 20, 2007

Dr. Robert Atlas, director of the NOAA Atlantic Oceanographic and Meteorological Laboratory--the parent organiztion of NOAA's Hurricane Research Division--testified at yesterday's Congressional hearing, on the science of QuikSCAT. In his written testimony, Dr. Atlas presented a good summary of QuikSCAT science:

There are three studies that address the potential degradation to computer hurricane forecasts that might result from the loss of QuikSCAT. Each of these studies has limitations that prevent definitive conclusions, and additional studies are needed. In my opinion, the preponderance of evidence from the three studies indicates that computer model forecasts of landfalling hurricanes, especially in the 2-5-day time range, could be degraded if we do not mitigate the loss effectively. Forecasters at the NHC are able to improve upon the computer forecasts, so that the potential degradation can be diminished. This is especially true as the storms are approaching land in the shorter time ranges. In addition, NOAA has recently developed an effective mitigation plan that would make substantial use of other satellites as well as enhanced aircraft observations.

I was pleased to see Dr. Atlas mentioning many of the uncertainties I've been drawing attention to. In his verbal comments, he offered a theory as to why the study done using the Navy NOGAPS model showed little effect of QuikSCAT on hurricane track forecasts. The NOGAPS model inserts a "bogus" vortex where a tropical cyclone exists, and this bogus vortex is resistant to modification by winds from QuikSCAT. The GFS model, used in the QuikSCAT study Bill Proenza cited, does not do vortex bogusing.

Dr. Atlas was not questioned about the uncertainties of QuikSCAT's impact on hurricane track forecasts, which surprised me. The general consensus among Congress members seemed to be that QuikSCAT was a valuable enough satellite that it deserved to be replaced, regardless of whether Mr. Proenza exaggerated its importance or not. No one talked about the need to cut any hurricane funding to pay for QuikSCAT, and a number of Congressmen thought we should be spending more. Congressman Ehlers (R-Michigan) said, "I think we have given short shrift to NOAA and its satellite program, considering how much is spent on the satellite programs for the Department of Defense, Global Positioning System, and NASA."

QuikSCAT science in the independent panel's report
The independent panel sent by NOAA to investigate management problems at the National Hurricane Center talked extensively about QuikSCAT (Attachment 9 of the written testimony of the administrator of the National Oceanic and Atmospheric Administration, Conrad Lautenbacher). The report said that mistrust of Bill Proenza by the staff was, in part, caused by disagreements about the science of QuikSCAT:

"Statements by the director about the limited lifetime of the QuikSCAT satellite and the resulting impact on forecasts--made without context or caveat--raised public doubt about the center's ability to perform its mission and distracted center staff from doing their jobs."
And: One senior hurricane specialist noted that the director repeatedly quoted him out of context about the potential impact of QuikSCAT's loss even after the director was told that he was in error.

Had I been a senior forecaster at the NHC, I would have raised the same issues, and spoken out against the misrepresentation of the QuikSCAT science that occurred. The director of the NHC must be honest with the uncertainties in the science if he is to be entrusted with the most important job in weather.

Jeff Masters

Politics

Updated: 10:55 PM GMT en Octubre 21, 2011

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Probe recommends Proenza's permanent removal; Atlantic and Hawaiian tropical update

By: JeffMasters, 2:11 PM GMT en Julio 20, 2007

At a Congressional hearing yesterday, results of the independent probe sent by NOAA to investigate management problems at the National Hurricane Center were presented by Dr. Jim Turner. Dr. Turner is deputy director of the National Institute of Standards and Technology, and was leader of the independent team of five people sent to NHC on July 2. Their report (Attachment 9) recommended the permanent removal of Bill Proenza as director of NHC (also called the Tropical Prediction Center, or TPC):

"The current TPC director should be reassigned and not be allowed to return to his position at the center. This should be done due to his failure to demonstrate leadership within the TPC rather than his public statements about the QuikSCAT satellite or NOAA leadership."

In his testimony, the administrator of the National Oceanic and Atmospheric Administration, Conrad Lautenbacher, presented some very damaging evidence against Mr. Proenza. Lautenbacher's written testimony includes a letter (Attachment 2) providing a detailed description of a conference call requested by 11 NHC employees (including 7 of 9 of the hurricane forecasters), with the acting head of the National Weather Service, Mary Glackin. If you want to better understand the NHC controversy, read Attachment 2 describing what was said during the June 19 meeting.

I'll make one more post this afternoon analyzing the science of what was presented at the Congressional hearing. Then, it's time to let this issue fade until the next Congressional hearing on the issue, tentatively planned for December or January. The tropics are starting to heat up, and it's time to focus on the coming hurricane season.

Tropical wave near Puerto Rico
A tropical wave near Puerto Rico is spreading clouds and thunderstorms over a wide area of the Eastern Caribbean, northern Lesser Antilles Islands, and surrounding waters. This wave is under about 20-30 knots of wind shear, thanks to the presence of an upper-level low pressure system to its northwest (Figure 1). This upper low is expected to stay in place an continue to bring hostile wind shear to the area the next few days. I don't expect the shear will allow anything to develop from this tropical wave.


Figure 1. Water vapor image from this morning showing the tropical wave near Puerto Rico, and the upper level low with dry air (dark colors) to its northwest. This upper level low sucking in moist air from the tropical wave, and is bringing hostile wind shear of 20-30 knots over it.

We will need to watch the waters off the Carolina coast on Saturday, when a cold front is expected to push off the coast. Most of the models are predicting the formation of a low pressure system along the tail end of this front by Sunday. This low may be an ordinary extratropical storm--or possibly a subtropical storm--due to the presence of high wind shear. NHC has put a Hurricane Hunter aircraft on standby to investigate the region on Sunday afternoon, if necessary. Even if the low is extratropical, it may be able to suck up plenty of tropical moisture and douse the mid-Atlantic coast and/or New England with heavy rains as early as Monday.

Cosme to skirt Hawaii
Residents of the Hawaiian Islands can relax a bit now, as it appears that Tropical Depression Cosme, will pass well south of the Big Island on Saturday. The edges of the outermost spiral bands will probably bring rains of 1-3 inches to the east side of the Big Island. Wind shear has fallen to 5-10 knots, and ocean temperatures are beginning to warm to 80F under the storm, and I expect Cosme will regain minimal tropical storm strength by Saturday. Satellite imagery of the storm shows that the amount of heavy thunderstorm activity has remained about constant so far today.

Jeff Masters

Politics

Updated: 10:55 PM GMT en Octubre 21, 2011

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New NHC revelations; Atlantic tropical update; Hawaii watches Cosme

By: JeffMasters, 1:47 PM GMT en Julio 19, 2007

There are no areas of interest to talk about in the tropical Atlantic today, but we will need to watch the waters off the Carolina coast on Saturday when a cold front is expected to push off the coast. The tail end of this front could serve as the focus for development of a tropical disturbance. The UKMET model is forecasting the development of a low pressure system here on Sunday. This low may be an ordinary extratropical storm, though, due to the presence of high wind shear.

Large amounts of dry air and African dust cover the eastern Atlantic, and this dusty air is moving westward towards the Caribbean. Tropical storm development is unlikely in this region for the coming five days. Thereafter, as a major shift in the Northern Hemisphere weather pattern puts a ridge of high pressure in place over the Eastern U.S., the Saharan dust outbreaks may decrease. Additionally, wind shear over the tropical Atlantic is expected to decrease substantially by next week, and chances of tropical storm formation are much higher next week than they were this week.

Hawaii eyes Cosme
Residents of the Hawaiian Islands need to keep an eye on Tropical Depression Cosme, which is headed towards the islands and may impact their weather by Saturday. Cosme is struggling with 10-20 knots of wind shear and ocean temperatures of about 25 degrees C. Satellite imagery of the storm shows that the amount of heavy thunderstorm activity has decreased some this morning, and it is possible that the unfavorable shear and SSTs will kill the depression before it encounters warmer waters and lower shear on Friday. If Cosme does survive the next 24 hours, it could re-intensify to a weak tropical storm and brush the Big Island of Hawaii on Saturday.


Figure 1. Sea Surface temperatures beneath Cosme were about 25 C (78 F), just below the 26 C threshold favorable for tropical cyclones. Cosme will be traversing a region of 24-25 C SSTs through Friday, then SSTs will warm to 25-26 as it approaches the Hawaiian Islands on Saturday.

More on the National Hurricane Center controversy
In an article published in the Houston Chronicle yesterday, senior hurricane specialist James Franklin said that employees of the center were not coerced by NOAA management into signing the July 5 letter of no confidence against director Bill Proenza. This view was echoed by NHC's top administrator in an Orlando Sentinel article. Franklin outlined a variety of reasons why the staff lost confidence in Proenza--Proenza lacked experience in hurricane forecasting and showed little interest in learning the science, ignored his employees to the tune of 2000 unread email from them, and lied to the press about his employees' reaction to his reprimand from NWS chief Mary Glackin.

Also in the Houston Chronicle story is the revelation that Proenza never applied for the position of director of NHC. He was demoted into it, according to Daniel Sobien, president of the National Weather Service Employees Organization. This raises the question, who put Proenza into the job? Why did they do it? Hopefully, this will get answered at today's congressional hearing. The list of people testifying include Bill Proenza; QuikSCAT expert Dr. Robert Atlas; emergency management officials who worked with Proenza; and the head of NOAA, Admiral Lautenbacher. With the exception of Lautenbacher, all these witnesses are likely to be allies of Proenza. Also testifying will be Dr. Jim Turner, deputy director of the federal agency NTIS (National Technical Information Service), who led the inspection team that showed up at NHC without notice on July 2. Dr. Turner's report was scheduled to be completed this Friday, July 20, but is now scheduled to be released to the Congressional panel today. Notably absent from the list of people called to testify is anyone from the National Hurricane Center. Also absent is a QuikSCAT science expert besides Dr. Atlas, who has thus far not addressed in his public comments, that I have seen, the very high uncertainties surrounding the impact of QuikSCAT data on track forecasts of landfalling hurricanes. In fact, in comments published in the Orlando Sentinel, Dr. Atlas claimed that Proenza's statement that loss of the loss of QuikSCAT could reduce the accuracy of hurricane-track forecasts by as much as 16 percent represents "the consensus of the scientific community." Well, that is not the case, as myself and senior hurricane specialists at the National Hurricane Center will attest to. I'll be sure to present a full analysis of the science presented--and the science left unsaid--at today's hearing.

The hearing charter for today's hearing raises these questions:

Why was Proenza chosen to be Director of the highest profiled Center at NOAA?

Beyond the items listed in the Glackin memorandum--which NOAA stresses was not a reprimand document and was not placed in Mr. Proenza's personnel file--are there any other actions that better justify the action to place Proenza on leave?

Why was there such a depth of dissatisfaction over Proenza's focus on a particular satellite?

What is needed to properly equip the Tropical Prediction Center, and are those resources available at this time?

Was the Tropical Prediction Center incapable of carrying out its core task of identifying, tracking and predicting hurricanes before the evaluation team was dispatched by Admiral Lautenbacher?

Jeff Masters

Politics

Updated: 10:56 PM GMT en Octubre 21, 2011

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Congressional NHC hearing tomorrow; Hawaii eyes Cosme

By: JeffMasters, 2:38 PM GMT en Julio 18, 2007

There are no areas of interest to talk about in the tropical Atlantic today, and none of the reliable computer models are forecasting tropical storm formation during the coming week. We will need to watch the waters off the Carolina coast on Saturday, when a cold front is expected to push off the coast. The tail end of this front could serve as the focus for development of a tropical disturbance.

Hawaii eyes Cosme
Residents of the Hawaiian Islands need to keep an eye on Tropical Storm Cosme, which is headed towards the islands and may impact their weather by Saturday. Cosme is a not-too-impressive 40 mph tropical storm now, thanks to 15 knots of wind shear and ocean temperatures about 25 degrees C. However, satellite imagery of the storm shows that it is maintaining a solid amount of heavy thunderstorm activity despite the wind shear and cool SSTs. I expect Cosme will be a tropical depression or weak tropical storm on Saturday when it passes close to the Hawaiian Islands, since SSTs are expected to increase and wind shear should decrease over the storm on Friday.


Figure 1. Sea Surface temperatures beneath Cosme were about 25 C (78 F), just below the 26 C threshold favorable for tropical cyclones. Cosme will be traversing a region of 24-25 C SSTs through Friday, then SSTs will warm to 25-26 as it reaches the Hawaiian Islands on Saturday.

Congressional hearing on the National Hurricane Center
On Thursday, July 19, from 10am until 12pm EDT, the House Committee on Science and Technology is holding a hearing called, "Tracking the Storm at the National Hurricane Center". You can check out some of the press releases and listen to a webcast of the hearing at the Committee web site. The Miami Herald, Orlando Sentinel, and Houston Chronicle have interesting stories on the upcoming hearing. The list of people testifying include Bill Proenza; QuikSCAT expert Dr. Robert Atlas; an emergency management official from the Gulf Coast states; and the head of NOAA, Admiral Lautenbacher. There may be others testifying, including Dr. Jim Turner, deputy director of the federal agency NTIS (National Technical Information Service), who led the inspection team that showed up at NHC without notice on July 2. Dr. Turner's report was scheduled to be completed this Friday, July 20, but is now scheduled to be released to the Congressional panel tomorrow. Notably absent from the list of people called to testify thus far: anyone from the National Hurricane Center, and a QuikSCAT science expert besides Dr. Atlas, who has thus far not addressed in his public comments--that I have seen--the very high uncertainties surrounding the impact of QuikSCAT data on track forecasts of landfalling hurricanes. I'll be sure to present a full analysis of the science presented--and the science left unsaid.

Jeff Masters

Politics

Updated: 10:57 PM GMT en Octubre 21, 2011

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Atlantic hurricane outlook for the last half of July

By: JeffMasters, 2:41 PM GMT en Julio 16, 2007

Atlantic tropical cyclone activity is usually low during the last half of July. Since the current active hurricane period began in 1995, eight of 12 years have had one or two named storms form during the last half of July. Two named storms formed in both 1995 and 2005. In 2005, we were already up to "E" in the alphabet at this point, so 2007 is certainly not going to be a repeat of 2005, thank goodness! As seen in Figure 1, most of the late July activity occurs in the Gulf of Mexico, but there are a few long-track "Cape Verdes" hurricanes beginning to occur. These are spawned by tropical waves that come off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed July 16-31. The Gulf of Mexico coast is the preferred strike location.

Sea Surface Temperatures
Sea Surface Temperature (SSTs) remained near average over the tropical Atlantic between Africa and the Lesser Antilles in July, thanks to plenty of African dust keeping sunlight from heating up the ocean. However, SSTs are 0.5-1.0 C above average over much of the Caribbean and Gulf of Mexico, so there is still good reason to expect an above average number of tropical storms and intense hurricanes this season--but not the 15 or 16 more named storms predicted by the Klotzbach/Gray team and TSR. I think it is more likely we will see 10-12 more named storms in the Atlantic this season, for a total of 12-14 when we include Andrea and Barry.


Figure 2. Sea Surface Temperature (SST) departure from average for July 16, 2007. Image credit: NOAA.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. There is less heat energy available this year than in 2005, which recorded the highest SSTs and TCHP ever measured in the tropical Atlantic. However, this is not true in the Western Caribbean, where we have very high TCHP this year. The African dust storms have not penetrated all the way to the Western Caribbean, and SSTs and TCHP have stayed above average. In the unlikely event we get an intense hurricane in late July, it would probably be in the Western Caribbean.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for July 14 2005 (top) and July 14 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation by tearing a storm apart. Wind shear below 8 knots is very conducive for tropical storm formation.

Wind shear during most of June and July has been above 20 knots along the two branches of the jet stream--the polar jet, which has been positioned along the U.S.-Canadian border, and the subtropical jet, which has been over the Caribbean. This pattern is apparent in this morning's wind shear map (Figure 4, top). However, a major shift the Northern Hemisphere weather pattern is expected over the next two weeks. The GFS model is predicting that the persistent trough of low pressure that has been over the Eastern U.S. will move off and be replaced by a ridge of high pressure about ten days from now. The subtropical jet will weaken, bringing pockets of very low wind shear all across the tropical Atlantic by the end of the month (Figure 4, bottom image). The shear will remain high enough to discourage tropical storm formation over the coming week, but chances for a named storm will increase sharply by the beginning of August.



Figure 4. Top: Wind shear analyzed by the GFS model at 00 GMT Monday, July 16 2007. Bottom: Forecasted wind shear for August 1, 2007. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the light purples in the image) will act to inhibit tropical storm formation. Wind shear below 8 knots (4 m/s, the lightest red color) is very conducive for tropical storm formation. Note the large increase in low wind shear areas expected by August 1 (bottom image, red colors).

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa. Despite the fact that the Sahel region of Africa has seen two straight years of above-average rains, which should result in soil stabilization and fewer dust outbreaks, 2007 has seen very high levels of dust coming from Africa. This activity continued over the tropical Atlantic during the first half of July, and I expect this activity to continue for the remainder of July. This dry air and dust will act as a major deterrent to any storms that tries to form between Africa and the Lesser Antilles Islands the remainder of July. With the coming Northern Hemisphere weather pattern shift, it is possible that the dry air coming off of the Sahara will fade some at the end of the month, though.

Steering currents
The steering current pattern for June and the first half of July featured a pattern much like we saw in 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. As I discussed in my blog on Friday the 13th, this steering current pattern is expected to shift next week, bringing a ridge of high pressure over the Eastern U.S. and an extension of the Bermuda High westwards over the U.S. This pattern will act to block recurvature of any tropical cyclones that might form in the last half of July. Such a pattern puts the Western Caribbean, Gulf of Mexico, and east coast of Florida at highest risk, as we saw in 2004 and 2005. Note that the the northern Lesser Antilles Islands, Puerto Rico, and the U.S. East Coast from the Carolinas northwards can expect reduced risk under this steering pattern. Steering current patterns are not predictable more than about two weeks in advance, and there is no way to tell if this new steering current pattern will remain in place for a few days or a few months.

Summary
Recent history suggests a 75% chance of at least one named storm occurring in the last half of July. This July, I put the odds at 50%, due to the unfavorable conditions for the coming week. Any storms that occur this July will probably be towards the end of the month, due to the lower shear, warmer SSTs, and potential for less African dust and dry air then. The areas of highest risk are the Western Caribbean, Gulf of Mexico, and east coast of Florida.

Jeff Masters

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Quiet in the Atlantic

By: JeffMasters, 2:29 PM GMT en Julio 14, 2007

There are no threat areas in the tropical Atlantic to discuss, and none of the reliable computer models are forecasting tropical storm formation over the coming week. Note that the Canadian CMC model has been regularly forecasting formation of tropical storms this season that have not occurred, so I am not including this model as one of our "reliable" models.

The long-range GFS model continues to forecast that the persistent trough of low pressure that has been present over the Eastern U.S. the past two months will finally move off, to be replaced by a ridge of high pressure by late July. This would bring a hurricane steering pattern much like we saw in 2004 and 2005, with increased risk for the Gulf of Mexico and reduced risk for the U.S. East Coast from the Carolinas northward. The east coast of Florida would remain at normal to above normal risk.


Figure 1. The eye of Typhoon Man-Yi showed pentagonal symmetry on July 12, 2007, when it was a Category 4 typhoon. Image credit: NASA.

Typhoon Man-Yi
In the Pacific, Typhoon Man-Yi battered Japan's Kyushu island yesterday, striking as a Category 1 storm. The typhoon killed one and injured 56 in Japan, according to preliminary media reports. The typhoon should weaken to a tropical storm by Sunday as the combined effects of winds shear, cooler waters, and interaction with land take their toll. Some weather links for those following the typhoon:

Japanese radar. Click on an area of interest to zoom in.

Latest satellite images of Typhoon Man-Yi, courtesy of NOAA.

Guam sector satellite images.

Awesome image of Man-Yi from NASA's Aqua satellite.

Jeff Masters

Updated: 2:33 PM GMT en Julio 14, 2007

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Major steering current shift; Typhoon Man-Yi wallops Okinawa

By: JeffMasters, 1:55 PM GMT en Julio 13, 2007

There are no threat areas in the tropical Atlantic to discuss, and none of the computer models are forecasting tropical storm formation over the coming week. However, there is there a major development to report--it appears likely that a major shift in the weather pattern will occur in late July across the Northern Hemisphere. If the GFS model is correct, the trough of low pressure that has been consistently in place over the Eastern U.S. will finally move off, to be replaced by a ridge of high pressure (Figure 1). This would bring a hurricane steering pattern much like we saw in 2004 and 2005, with increased risk for the Gulf of Mexico and reduced risk for the U.S. East Coast from the Carolinas northward. The east coast of Florida would remain at normal risk. The GFS model has been inconsistent in its prediction of the timing of this shift, but has been persistent enough about it that I'm forecasting a 70% likelihood of this major pattern shift occurring by the end of July. Such a shift would bring the western U.S. some relief from the current heat wave, and bring high heat and air pollution problems to the Midwest and East Coast. How long such a shift might last is impossible to predict--it could last for a week, or could remain in place for the remainder of hurricane season. I'll have an updated forecast on this pattern shift Monday, when I issue my bi-weekly hurricane outlook.



Figure 1. Observed 500 mb heights at 00 GMT today (top), and forecast height in two weeks' time from the GFS model(bottom). The white lines in these plots show how close to the surface a pressure of 500 millibars (mb) is found. When there is low pressure aloft, due to a trough of low pressure, the height at which a pressure of 500 millibars is found moves closer to the surface, and one sees a "U" shaped area of 500 mb height lines. We can see a trough over the Eastern U.S. in the top plot. When a ridge of high pressure occurs aloft, the height at which a pressure of 500 millibars is found moves higher up in the atmosphere, away from the surface, and one sees an upside-down "U" shape to the height lines. A ridge of high pressure is apparent over the Eastern U.S. in the bottom plot. This ridge of high pressure over the Eastern U.S. will be accompanied by an extension of the Bermuda High to the west over the the U.S., which will act to block recurvature of hurricanes.

Typhoon Man-Yi
In the Pacific, Typhoon Man-Yi battered Japan's Okinawa Island this morning, striking as a super typhoon with 155 mph winds. Naha, Okinawa recorded sustained winds of 76 mph with gusts to 105 mph (Figure 1), and a pressure of 939 mb. This was very close the the minimum pressure estimated by satellite, 937 mb. Media reports indicate substantial damage occurred on Okinawa, and over 100,000 people lost power. Twelve crew members of a Chinese ship were missing after the vessel sank some 600 km northwest of Guam in strong winds and high seas. Man-Yi is expected to make landfall on the Japanese island of Kyushu Saturday. However, the storm should weaken to a Category 1 storm by landfall, as wind shear from an approaching trough of low pressure has already reached 20 knots on the west side of the storm, and is expected to increase further. Some links for those following the storm:

Japanese radar. Click on an area of interest to zoom in.

Latest satellite images of Typhoon Man-Yi, courtesy of NOAA.

Guam sector satellite images.

Awesome image of Man-Yi from NASA's Aqua satellite.

Current conditions in Japan:
Kagoshima, southern Japan
Miyazaki, southern Japan
Tanegashima, southern Japan


Figure 2. Wind trace from Okinawa airport during Typhoon Man-Yi. Note the shift in wind direction as the eye passed over, and sharp drop in wind speed at this time.

Jeff Masters

Updated: 7:26 PM GMT en Julio 13, 2007

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Restoring confidence in NHC

By: JeffMasters, 12:24 PM GMT en Julio 11, 2007

There are no threat areas in the tropical Atlantic to discuss, and none of the computer models are forecasting tropical storm formation over the coming week. In the Pacific, an exceptionally large Category 4 typhoon, Man-Yi, will pass close to Okinawa on Friday, and hit Japan on Saturday. Winds at Okinawa have been as high as 50 mph with gusts to 70 mph.

Some links on Man-Yi, sent to me by Jim Edds:

Live camera feed from Southern Okinawa:

click on the pic arrow on the bottom right.

Okinawa radar.
click on Okinawa to zoom in - awesome shot

Camera feed with some audio.
click on the first "no image" box then select "report 17/66"


Latest satellite image of Typhoon Man-Yi, courtesy of NOAA.

Restoring confidence in the NHC
Interim National Hurricane Director Dr. Ed Rappaport has two immediate tasks--restoring morale fractured by Bill Proenza's turbulent 6-month tenure, and restoring public confidence in the Hurricane Center's ability to do their job. With the steadying influence of Dr. Rappaport, a highly respected and talented hurricane scientist, I expect that the staff of NHC will put out their best hurricane forecasts ever this season. Aiding in this endeavor will be the availability of a new hurricane tracking, intensity, and storm surge model called the HWRF--Hurricane Weather and Research Forecast Model. In addition, several of the other reliable models used by the forecasters, such as the GFS and GFDL, have had upgrades since last hurricane season. Furthermore, the Air Force Hurricane Hunters will be carrying the SFMR instrument for the first time, which can measure winds speeds at the ocean surface everywhere the aircraft fly.

Forecasters at the National Hurricane Center made their best track forecasts ever for storms in the Atlantic in 2006. The mean track errors for 12 to 72 hour forecasts were 15% - 20% lower than during 2001-2005. Track errors for Atlantic storms have improved about 50% in the past 15 years (Figure 1), a remarkable achievement that has undoubtedly saved lives and hundreds of millions of dollars. The track error in 2006 for a 24 hour forecast was 58 miles; 112 miles for a 48 hour forecast; and 171 miles for a 72 hour forecast. Track errors for 96 and 120 hour forecasts were 236 miles and 305 miles--the second best on record (2003 set the record). NHC's long-range 120 hour forecasts had a significant bias to the west of 94 miles--about double the bias of what the computer models were forecasting. Thus, when the models correctly called for systems to recurve out to sea, NHC human forecasters tended to resist following what the models were saying.



Figure 1. Track forecast skill since 1990 in the Atlantic for the official NHC forecasts. Track errors are given in nautical miles (100 n mi = 115 miles). Skill is rated compared to a "zero skill" forecast using NHC's CLIPER5 model. The CLIPER model (short for CLImatology and PERsistence) is a model that makes a forecast based on historical paths hurricane have taken, along with the fact that hurricanes tend to keep moving in the direction they are going (i.e., their current motion persists).

Intensity forecasts
Intensity forecasts since 1990 have shown little or no improvement, and 2006 was no exception (Figure 2). One encouraging result was the emergence of the GFDL's intensity model as the best intensity model for 2006. This is the first time that a non-statistical model has made the best intensity forecasts. With the major improvements that were added for the 2007 version of the GFDL, plus the availability of the HWRF model, I am hopeful that this year will see the first noticeable improvement in intensity forecasts since 1990.



Figure 2. Intensity forecast skill since 1990 of the official NHC Atlantic forecasts. Intensity errors are given in knots (10 knots = 11.5 mph).

Jeff Masters

Politics

Updated: 10:57 PM GMT en Octubre 21, 2011

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Bill Proenza gone; tropical update

By: JeffMasters, 8:35 PM GMT en Julio 09, 2007

With hurricane season fast approaching and internal strife threatening "the effective functioning of the National Hurricane Center", as stated in a letter signed by 23 of NHC's 49 employees, NOAA did the best thing by reassigning director Bill Proenza this afternoon. Conrad Lautenbacher, the head of the National Oceanic and Atmospheric Administration, announced Proenza has been placed on leave "until further notice."

The reassignment puts NHC deputy director Ed Rappaport, 49, into the director's hot seat. I greatly respect Dr. Rappaport, who has done a great job as deputy director and is a highly skilled hurricane forecaster. Dr. Rappaport has a Ph.D. in Atmospheric Sciences from Texas Tech. He began work in 1988 at NHC, and served as one NHC's Hurricane Specialists before becoming chief of the Technical Support Branch. He is the best choice for director of NHC. He had wide support to become director last year when Max Mayfield retired, but turned down the job due to family reasons.

Tropical update
There are no threat areas in the tropical Atlantic to discuss, and none of the computer models are forecasting tropical storm formation over the coming week. A cold front is expected to push off the U.S. East Coast by Sunday, and we will have to watch the waters off the North Carolina coast then for development when the front stalls out. In the Pacific, an exceptionally large Category 1 typhoon, Man-Yi, is expected to become a major typhoon, and will threaten Japan late this week.

Jeff Masters

Politics

Updated: 10:58 PM GMT en Octubre 21, 2011

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More heat

By: JeffMasters, 1:40 PM GMT en Julio 09, 2007

An assessment team from NOAA headquarters returns to the National Hurricane Center today to interview staffers and director Bill Proenza about the on-going upheaval at the center. Last week, most of the senior staff called for Mr. Proenza to step down. I continue to support the senior staff on this issue, as detailed in a blog from last week. It's up to the NOAA assessment team to sort things out now, which will not be easy. I hope that the NOAA assessment team fairly considers the evidence, and that wisdom prevails in this unfortunate conflict.

Tropical Update
Fortunately for all concerned, the tropical Atlantic is very quiet at present. There are no threat areas to discuss, and none of the computer models hint at anything developing over the coming week. It's a different story in the Pacific, where tropical Storm Man-Yi is expected to become the season's first Category 3 or higher typhoon. Man-Yi could threaten Japan late this week.

More heat
Friday's high temperature of 129 degrees in Death Valley was only five degrees away from the hottest temperature ever recorded in North America--the 134 degrees (you guessed it) in Death Valley, back on July 10, 1913. Temperatures cooled off over the weekend, but not a lot--Sunday's high was 120 degrees (but it was a "dry" heat!) The heat will continue over the West this week, but we have likely witnessed the peak temperatures from this heat wave. With thunderstorm activity expected to pick up this week across the West, expect plenty of lightning-triggered fires to erupt. Utah is already reporting its biggest forest fire in history, and we can expect one of the worst summer fire seasons on record across the Western U.S.

June wasn't exceptionally hot across the U.S.--the National Climatic Data Center reported that June 2007 was the 23rd warmest and 33rd driest June in the historical record (since 1895). The period January - June was the 18th warmest on record. July will probably not set any heat records for the U.S. as a whole, despite the Western heat wave, since a major trough of low pressure is forecast to bring unseasonably cool air across the Midwest and Northeast later this week.

Good-bye, Margie!
View From the Surface blogger Margie Kieper is retiring from blogging as of today. She wants to focus her energies on contributing to the science of tropical meteorology, and hopes to become a co-author on scholarly journal articles. Margie is one of the best researchers I've worked with, and I'm sure she'll do well. We'll miss her thorough and informative blog posts!

Jeff Masters

Heat Politics

Updated: 11:12 PM GMT en Agosto 16, 2011

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Transcript of the NHC press conference; QuikSCAT science

By: JeffMasters, 8:27 PM GMT en Julio 06, 2007

The National Hurricane Center political controversy continues today. In an Associated Press story released this morning, Senior Hurricane Specialist James Franklin of the National Hurricane Center commented on Bill Proenza's QuikSCAT claims, saying:

"He has been very loudly saying if it failed our forecasts for landfalling storms would be degraded, that warning areas would need to be expanded. None of that is the case, and he knows that we feel that way. The science is not there to back up the claims that he's making."

This was the same case I made in my blog yesterday. However, in comments published in the Miami Herald today, Dr. Bob Atlas, a QuikSCAT scientist who runs NOAA's Atlantic Oceanographic and Meteorological Laboratory on Virginia Key, rose to defend Proenza. To quote from the Herald:

He said the report challenged by Masters, even if not yet published, appears to be a "rigorous study" that provides the "most comprehensive study of QuikSCAT data related to hurricane predictions."

Atlas said nothing he has heard Proenza say about QuikSCAT has made him wince, though Atlas added that NOAA is developing ways to mitigate the loss of QuikSCAT data.

In addition, he said, Proenza's estimates of 16 percent and 10 percent have been misunderstood: They apply to the accuracy of one of many computerized forecast models rather than actual, end-result predictions by hurricane forecasters.

"Bill's worked very hard and very well to position the hurricane center to interact well with researchers," Atlas said.


Dr. Atlas was mis-quoted by Time Magazine, who printed this:

Bob Atlas, director of NOAA's Atlantic Oceanographic and Meteorological Laboratory in Miami, insist that Proenza's concerns "are very well founded. QuickScat is the most valuable forecasting tool." Atlas says he applauds Proenza's outspokenness, predicting it will "accelerate the effort to replace QuickScat with an even better scatterometer satellite."

I talked with Dr. Atlas this morning, and what he actually said is that "NCEP's Ocean Prediction Center (OPC) have referred to QuikSCAT as the most valuable tool they have." OPC issues the high seas marine forecasts and warnings for the North Atlantic and North Pacific. Dr. Atlas did not say QuickSCAT is the most valuable forecasting tool for hurricane forecasting which it is not. Dr. Atlas and I both agree on what the science says about QuikSCAT. I respect his support for Proenza, and hope that Proenza's superiors in Washington take into account all the facts in the case. I did my best to present what I know of the science in my blog yesterday. No one knows the full story of what's going on at NHC, but this morning's press conference, done by staff members at NHC who oppose Proenza, will help clarify things. A transcript was sent to me by WTVJ, the NBC Station in Miami.

Transcript of this morning's press conference

Senior Hurricane Specialist James Franklin
We have been a family here, we are a small group of about 50 people. When things are really happening, we've got a Katrina out there or a Rita type of storms, everybody needs to stop what they're doing and pull together and make sure our message gets out and that we're doing the best job that we can to make the best forecast. We've got a lot of people pulling together to do that. That takes a certain amount of teamwork and appreciation of sense of family and he's destroying that, he's destroying that.

He's divided the staff, and it's hard to know how we're going to be able to come together with him here. One thing that happened yesterday when the staff met, and talked about these issues and a lot of people learned for the first time about some of the issues going on yesterday, and that brought a lot of the staff together. You saw a number of people speaking out both in terms of 3 to 23 yesterday. We found out what was really going on here. and I think you're going to see more later on.

I was very very gratified, we had a wonderful meeting with staff, including those who have been prior supporters of Bill. And we're learning a lot of things for the very first time. There we're a number of people who agreed with us, didn't like the idea of going to the press, but felt he needed to go, there are a fair number of people who didn't sign the letter for that reason. They wanted to keep it in house, and I certainly understand that. About 70-percent of the people who were in the discussion yesterday, put their names on the paper.

I think we've learned an awful lot about Bill here, during the last six months that maybe we didn't know.

We would have liked to have seen Bill realize that he didn't have the support of the staff and step down. That's not going to happen apparently. The process, the Dept. of Commerce process, I imagine needs to go forward. I think it would be nice if they could take him out of the office while that process goes on, those are not decisions we can make.

Lixion Avila-Senior Hurricane Forecaster
-Been here longer than any other forecaster
-Worked for 5-hurricane directors

I was Bill's stronger supporter, I went with him to the Caribbean with the hurricane hunter plane. To develop the hurricane hunter plan, like I did with all the directors. And I'm very upset (loud truck drives by) that he's been misrepresenting the views of the National Hurricane Center, and the hurricane plan. That plan was developed by the previous five hurricane directors, it's a jewel, it's the best in the world and it's been something that Neil Frank, Bob Sheets and Jerry Jarrel and developed for 20-years in six months he wants to destroy that plan.

For example he, I'm a scientist not a manager, and I don't know anything about management, but I can tell you that he came to my office telling me that he wants my advice, that he can not work here if he doesn't hear my advice.. very helpful with the previous directors, and he asked me, and I said the first thing you need to do is quit talking about that QuikSCAT and tell him that is out of line, will help all the problems. And he says he will do that, instead he goes back to the media, and you don't publish that you only publish the good things he said.

He said that we don't want to work with him, because he brings many good ideas, and we don't want to do that. I want you to know that he has not made a hurricane forecast since 1964.

That satellite, I gave that example to many people here. There are many things more important than that satellite. Of course I want that someone to have that satellite. The example I gave everybody is like having a BMW with leather seats. If you don't have leather seats that BMW is going to ruin, and we are going to make a very damn good forecast this year, with Bill or without Bill, and I think. I'm being very emotional, because I was his strongest supporter and I feel betrayed.

I was the last forecaster to join the group. They were smarter than me, I was giving him one more chance. Two day's ago when he came to my office and said please, what should I do to solve this problem? And I was very naive and I told him you need to stop fighting, pretending you're David against Goliath, and all those things with NOAA. The public thinks you're a hero, but you're not. You just need to develop your time and saving the hurricane program that your predecessor developed so nicely, this castle that has been done here. and he went back and said he was going to do that, he went to the media and said the opposite, and that's the end, thank you.

James Franklin
I want to say something about the QuikSCAT issue because, because that's important. The QuikSCAT satellite, is important to us, it does a lot of good things for us. We want a next generation advanced instrument, however there are a lot of things that current instrument cannot do, and by misrepresenting the case for that satellite, he has made it seem so urgent and so important. That what we're afraid of, that we'll get a quick fix, a copy of the kind of thing with existing technology. And within a couple of years we'll be in exactly the same position same situation. QuikSCAT is not a tool to help us improve track forecasts, that's how it's been misrepresented. Bill waves this NOAA report that some of my colleagues worked on and said look this is it. That report did not address track forecast accuracy, that is another one of the misrepresentations.

QuikSCAT is important to help us understand the size of the wind field, the strength, the current instrument has a lot of trouble with rain, a lot of rain in tropical cyclones. We need to move forward if we take the time develop the technology further and in a few more years get at the technology that really helps us get at the intensity problem, that's where our forecast problem really is. We've made great strides with track, as you know we're having a lot more problems with intensity, and doing the QuikSCAT problem correctly, taking our time, developing new technology is one of the tools that we need to help solve the intensity problem. But because of the way it's been portrayed we're afraid that there's going to be a quick fix that's not going to address the track problem, and it doesn't address the track problem and it isn't going to end up helping us with what the forecasters really know will help us.

We've see members of the Congress talking about how the information from the recognizance aircraft are inferior to QuikSCAT, we're afraid that somebody might get it in their heads to fund a stopgap QuikSCAT to take funds from recon aircraft. There is no comparison, there is not a forecaster here who believes QuikSCAT is more important than recon aircraft or other tools we have. But because this issue has been misreported we're afraid we might lose what we have.

We've got forecasters still back at there desks doing their jobs and they'll continue doing that. But there's a lot of people losing sleep over this, and as we get into august September, October, I don't think you want a bunch of tired sick, forecasters working the forecast desk. I think it takes a full effort. It's not just about doing our jobs, we need to go over and beyond when those storms are coming, and that's becoming harder to do.

I think when things get busy, it's going to be harder for us to work effectively with the situation we have here.

Vivian Jorge, Administrative Officer
As far as myself in the administration, since Bill got here, is the turmoil in the administration, because in my sense, bill(sat breakup) likes controversy. And I myself have been asked to do things that I know are not procedure but have been asked to do because that's the way he wants things done, and I've worked at hurricane center since 1985.

Unfortunately I think a director needs to unite his staff and he needs to be a calming person. It doesn't need to be a no new ideas. All the directors have different ideas.. from Neil on down to Max, they were different, they were not the same, their management styles were not the same, but they united the staff, the listened to the staff, especially the folks who have been here for so many years. .. and I think in the case of bill he doesn't feel that's necessary, he always feels he knows best. And that again in our case, there's never been so many closed doors, so much intrigue at the hurricane center as now and that's really unfortunate. I can't tell you how proud I am to work here.

--End of Press Conference

QuikSCAT science
Enough of politics, let's talk science! I've communicated several times over the past few weeks with Dr. Paul Chang, a NOAA QuikSCAT scientist whose QuikSCAT web page I've linked to hundreds of times in my blogs over the past two years. He did not want to comment on the politics of the QuikSCAT issue (smart man!), but did ask me print these comments:

The need for an operational ocean surface vector wind satellite system like QuikSCAT (or actually better) goes much further than the hurricane issue, and the push for it started long before Bill Proenza became the NHC director. NHC actually wants/needs something better so that it can provide them with reliable and accurate information (intensity and structure) within all hurricanes. A few other users of QuikSCAT data include: The Department of Defense's Joint Typhoon Warning Center in Pearl Harbor, which has a much larger area to forecast for. They have no Hurricane Hunter data and much less surface and upper air data to work with, and thus use QuikSCAT winds quite a bit. This is a similar situation for NOAA's Central Pacific Hurricane Center located in Hawaii. QuikSCAT has also had significant positive impacts at the Ocean Prediction Center, which issues the high seas marine forecasts and warnings for the North Atlantic and North Pacific. This has led to the introduction of a warning category for hurricane force winds for the most dangerous extratropical cyclones. I know of at least a few private marine weather companies that routinely use QuikSCAT. The Australians, French and many others use QuikSCAT routinely for tropical storm forecast/analysis, and for marine weather in general.

The track degradation impact numbers that Bill Proenza has been stating publicly come from a limited data study for the 2003 season in the Atlantic with the GFS model only. I believe Bob Atlas did some earlier work studying the impact of QuikSCAT on Hurricane Cindy using an earlier version of the NCEP global model. Both of these studies did show promising positive impacts. They are of course limited studies, and a more in-depth study is warranted.

The GFS model hurricane track forecasts are just one piece of guidance that the NHC human forecasters use to generate the official track forecast, so the impact in a particular model guidance package does not directly translate to the same impact in the actual NHC officially issued track forecast. Additionally, QuikSCAT data are also used directly by forecasters at NHC and elsewhere, but this impact tends to be more difficult to quantify.

The aircraft are a very important hurricane operational and research tool, and no one involved in the QuikSCAT follow-on effort has ever said QuikSCAT (or its successor) should or could replace the role of the hurricane aircraft flights, just as no one has said that aircraft could replace the role of satellites. They are very complementary platforms, but they fulfill different roles.


It would be a shame if in the hubbub over Bill Proenza's push to get a replacement for the QuikSCAT satellite we lose sight of what all the scientists agree on--QuikSCAT is a vital tool in weather prediction that needs to be replaced with a better satellite. Both Dr. Atlas and Dr. Chang are working on research specifically designed to study just how much impact QuikSCAT has on landfalling hurricanes in the Atlantic, which no studies have yet quantified.

Read Margie' Kieper's View From the Surface Blog for more on the QuikSCAT/Bill Proenza matter.

Jeff Masters

Politics

Updated: 11:02 PM GMT en Octubre 21, 2011

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Revolt at NHC; tropical update

By: JeffMasters, 1:24 PM GMT en Julio 06, 2007

The extraordinary political turmoil at the National Hurricane Center (NHC) continued yesterday, with the release of a statement signed by nearly half of the staff calling for the immediate dismissal of director Bill Proenza. Front page stories in both the Miami Herald and Florida Sun-Sentinel detail the letter, which reads: "An unfortunate public debate is now occurring over the ability of the National Hurricane Center to meet its mission. The undersigned staff of the National Hurricane Center has concluded that the center needs a new director. The effective functioning of the National Hurricane Center is at stake. The staff of the National Hurricane Center would like nothing more than to return to its primary mission of protecting life and property from hazardous tropical weather, and leave the political arena it now finds itself in." The letter is signed by 23 of the center's 49 employees, including almost the entire senior staff. Many NHC employees were on vacation, and did not have the opportunity to sign the letter.

The articles in the two newspapers also quote my blog from yesterday, where I present the case against Bill Proenza--his misrepresentation of the science of how much the QuikSCAT satellite influences hurricane track forecasts. I'll have more to say on the matter this afternoon, when I've had a chance to process some of the feedback on this.

Tropical update
A low pressure system (96L) with a well-defined spin is about 550 miles east of the Lesser Antilles Islands, moving westward towards the islands at 10-15 mph. This low continues to show sporadic heavy thunderstorm activity, but has been unable to overcome the large amount of dry air it is embedded in. It would appear that 96L's window of opportunity for developing into a tropical depression has closed, as wind shear has risen to 20 knots and is expected to remain at least 20 knots for the next two or three days. None of the reliable computer models develop the system into a tropical depression.


Figure 1. Model tracks for 96L, the low pressure system approaching the Lesser Antilles Islands.

New disturbance off the east coast of Florida
An area of disturbed weather has developed off the east coast of Florida along an old frontal boundary. Long range radar out of Melbourne, FL shows a large disorganized area of showers off the coast. The area is under 20-25 knots of wind shear, and the shear is forecast to remain above 20 knots for at least the next two days in the region, which should prevent any development. The GFS computer model shows this disturbance moving off to the northeast over the weekend, but it could bring heavy rains to Florida and the Northwest Bahamas Friday and Saturday before it does so. None of the reliable computer models develop the system into a tropical depression.

Jeff Masters

Politics

Updated: 11:02 PM GMT en Octubre 21, 2011

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Challenging Bill Proenza's QuikSCAT numbers

By: JeffMasters, 5:04 PM GMT en Julio 04, 2007

A political storm engulfed the National Hurricane Center this week, with a majority of the senior hurricane forecasters calling for Bill Proenza's removal as director. The most visible issue revolved around the extraordinary focus on the aging QuikSCAT satellite. The public argument put forth by Mr. Proenza was that QuikSCAT data was so vital to hurricane track forecasting that without it, track forecast errors would increase significantly, leading to larger warning areas and increased costs for evacuation and emergency planning.

Focus on QuikSCAT--out of proportion?
On March 16th Proenza went public with the QuikSCAT concerns and associated statistics for the first time, stating that "two- and three-day forecasts of a storm's path would be affected. The two-day forecast could be 10 percent worse while the three-day one could be affected up to 16 percent," with the conclusion," that would mean longer stretches of coastline would have to be placed under warnings, and more people than necessary would have to evacuate." As a result of these comments, a perception arose in the public and among lawmakers that without QuikSCAT, NHC would not be able to provide accurate hurricane forecasts. Legislation was hastily introduced into both the House and Senate to provide an immediate replacement for the $375 million satellite.

Proenza's statements raised several questions: 1) Why the focus on track forecast errors in landfalling situations, when QuikSCAT was widely known to be used in intensity forecasting and for tropical cyclones too far at sea to be accessed by the Hurricane Hunters? 2) Could such specific and significant gains in track forecast error truly be attributed to QuikSCAT? Where did these numbers come from, and why was no uncertainty being attached to them?

Since QuikSCAT data became available, starting in 1999, average track errors for 48-hour and 72-hour forecasts have been reduced by 43 miles and 62 miles respectively. Fully one quarter of this improvement was being attributed by Proenza to QuikSCAT. This was an extraordinary performance increase to attribute to one satellite, and seemed doubtful.

We find out where the QuikSCAT numbers came from
In mid-June, Margie Kieper and I asked Proenza to comment on how he got his QuikSCAT numbers. He cited an unpublished study, "A Two Season Impact Study of Four Satellite Data Types and Rawinsonde Data in the NCEP Global Data Assimilation System", by Tom H. Zapotocny, James A. Jung, John F. LeMarshall and Russ E. Treadon. I contacted one of the authors, who informed me that the study was submitted for publication on January 26, 2007, and accepted for publication in the journal Weather and Forecasting on May 23, 2007. It will probably appear in the October-November time frame, according to the publisher. This raises an immediate problem, since only a privileged few are able to read unpublished research. This limits the possibilities for an informed debate on the issue, and basing important policy decisions on unpublished research is thus normally to be avoided. However, making accurate hurricane forecasts is important enough that such considerations can be excused. Proenza didn't give me any details on the study, other than the fact that QuikSCAT data improved 72-hour and 48-hour hurricane track forecasts by 16% and 10% respectively, for a select group of storms from the 2003 hurricane season. One of the authors graciously sent me a copy of the study, though, and after reading it, I had these observations:

1). The study looked at a very limited number of cases over a six-week period during 2003--only 19 cases were available for 72 hour forecasts. The 19 cases were not 19 storms, just 19 separate forecasts from the 4 hurricanes and 2 tropical storms that occurred during the 6-week study period. This sample is too small to draw definitive conclusions about the impact of the QuikSCAT on tropical cyclone forecasts. The two longest-lived storms during the test period were Fabian and Isabel, storms that spent the majority of their lifetimes far away from land. Since the quality of the observing network increases close to land, particulary when reconnaissance data from the Hurricane Hunters is available, it is reasonable to conclude that the impact of the QuikSCAT data for storms within 72 hours of landfall would be less than for the sample as a whole. The study was not primarily designed to study tropical cyclone track accuracy, so there was no separation out of the cases we really care about--storms 72 hours or less from landfall.

2). The study was done with only one model, the GFS. NHC official forecasts make use of several models, including the GFDL, UKMET, NOGAPS and ECMWF. Consequently, a change in the accuracy of a single model will have only a partial effect on NHC official forecast accuracy. As far as I know, there have not been studies done of the impact of QuikSCAT on tropical cyclone forecasts in the GFDL, UKMET or the ECMWF models. Past studies on the impact of dropsonde data from the Hurricane Hunters, however, show that the GFDL is less sensitive to these data than the GFS is.

3). When I attended the AMS hurricane conference in May 2006 in Monterey, I came across a poster presentation by Dr. Jim Goerss that evaluated the impact of QuikSCAT on the NOGAPS model. His study was far more comprehensive, and included 12 hurricanes, 5 typhoons, and 7 tropical storms from a 6-week period in 2004. The number of cases was 212 at 72 hours, eleven times as many as the study Proenza cites. Dr. Goerss found that QuikSCAT probably improved 24-hour track forecasts by 2.5% (90% confidence of this), but at all other forecast times (48, 72, 96, and 120 hours), QuikSCAT had no statistically significant effect (i.e., zero effect).

It is hard to compare the results from these two studies, since they used two different data assimilation systems. We do not know if they used all the data, or how they treated the vertical impact of the data. The uncertainties are high, and Proenza's simple statement that QuikSCAT data improves hurricane tracks forecasts by 10% and 16% is unreasonable, without at least making mention that these numbers are highly uncertain.

I believe that NHC official forecasts for landfalling storms in the Atlantic would not be significantly affected by the loss of the QuikSCAT satellite. I can't think of a hurricane scientist out there who would defend using a study with only 19 cases that didn't focus on landfalling storms, to make the case Proenza is making--particularly in light of the data from the unpublished Goerss study showing no effect of QuikSCAT data on NOGAPS model tropical cyclone track errors. Proenza should have at least attached some measure of uncertainty to his numbers, which he did not.

One could argue that the study cited by Proenza has undergone peer review, and is thus the only scientific study one can use to make arguments on QuikSCAT's effectiveness. The Goerss study has not been published in a journal, and has not undergone peer review. However, Proenza was making his QuikSCAT accuracy arguments in March, two months before the Zapotocny study he cited had been accepted for publication.

QuikSCAT misconceptions
The numbers pushed by Proenza have led to some potentially serious misconceptions about QuikSCAT. The Congressional Record has this to say about QuikSCAT:

"A single plane gathering data is like a tiny fishing line collecting data only along the single strand of the line. The satellite, on the other hand, provides rich, detailed data horizontally from one side of the storm to the other side, and vertically, from the ocean surface to the top of the storms swirling winds. The QuikSCAT is like a detailed MRI."

Well, QuikSCAT is not like an MRI, it just measures the ocean surface winds. In a letter written by Representatives Melancon and Klein in support of H.R. 2531, there are comments that data from the reconnaissance aircraft are inferior to the data from the QuikSCAT:

"Short-term options for replacing QuikSCAT include hurricane hunter aircraft, buoys, and foreign satellites--all of which will collectively produce inferior data."

There is not a hurricane forecaster anywhere that would trade hurricane hunter data for QuikSCAT. Lawmakers may start cutting aircraft reconnaissance with misconceptions like this. That would be a disaster.

I would hate to lose the QuikSCAT satellite, and have been calling for a replacement since before Mr. Proenza came on the job. QuickSCAT data is invaluable in identifying weak systems and in defining storm structure, particularly of outer wind radii of 34 knots and 50 knots. This is particularly true outside of the Atlantic, where there are no Hurricane Hunter flights, and in the Atlantic beyond where the Hurricane Hunters can reach. Track forecasts for tropical cyclones in the Pacific and Indian Oceans may benefit from QuikSCAT data, since Hurricane Hunter information is not available. QuikSCAT also helps identify when a tropical depression or tropical storm is intensifying.

Besides hurricanes, the QuickSCAT data is invaluable to the Ocean Prediction Center, which now issues hurricane force wind warnings for extratropical storms in the Atlantic and Pacific. Search and rescue missions, and the U.S. Navy also greatly benefit from QuikSCAT. QuikSCAT should be replaced, but not due to a rush knee-jerk reaction that will get us a replacement with old technology. NHC needs a "next-generation" scatterometer, one that has greatly improved capabilities to help tackle the structure and intensity problem. We should take our time, and deal with a gap in coverage, if it gets us an instrument that has higher resolution, higher saturation speed, and is not adversely affected by rain. Such a gap would not put the public at risk.

It greatly troubles me that the most visible and admired member of my profession has failed to use good science in his arguments for funding a replacement of the QuikSCAT satellite. The Director of the National Hurricane Center needs to be an able politician and good communicator, but being truthful with the science is a fundamental requirement of the job as well. Mr. Proenza has misrepresented the science on the QuikSCAT issue, and no longer has my support as director of the National Hurricane Center.

Other critical concerns--lost in the hubbub?
We strongly support many of the valid concerns Proenza has raised. Of particular concern are the slashing of critical research funding for the Joint Hurricane Testbed (JHT) from $1.7 million to $1 million, and the lack of adequate yearly increases to the National Hurricane Center budget. Both of these important concerns still remain to be addressed; they were quickly overshadowed by a frantic campaign by lawmakers to fund a new QuikSCAT satellite. The JHT provides the means for promising research to be tested in the NHC operational environment, usually resulting in a successful transition to an operational product at NHC. This program has been extremely successful, and its budget should have been increased, not slashed. As hurricane activity has increased dramatically over the last twelve years, NHC's budget should have increased accordingly, but it did not.

Proenza also raised legitimate concerns about NOAA's effort to promote their "Corporate Identity" by renaming the National Hurricane Center and National Weather Service. The new organizations would be called the "NOAA Hurricane Center" and the "NOAA Weather Service". He also justly complained about NOAA's plan to spend between $1.5 million and $4 million on a "bogus" 200-year NOAA anniversary celebration.

While wanting to take a neutral stand as to whether to call for Proenza's dismissal, Senior NHC Hurricane Specialist Lixion Avila clearly shares the concerns that have been put forth by the other senior forecasters Richard Pasch, James Franklin, and Richard Knabb, and former director Max Mayfield. Avila noted, "If I [was] the director of the hurricane center, I would not spend my time fighting for QuikSCAT--I would be fighting to make sure that the reconnaissance planes are always there." That leaves a vacationing Jack Beven as the only senior hurricane forecaster to not comment publicly on the issue. Max Mayfield has refrained from making public comments on the deteriorating situation these past months, but all of his comments in the Miami Herald article lend support for the hurricane forecast staff. Given his previous experience in the position of NHC Director and his successful tenure, his feedback counts tremendously.

With the busiest part of hurricane season just a few weeks away, expect a decision on Bill Proenza's tenure to be made soon.

Jeff Masters and Margie Kieper

Having lost the support of most of his senior forecasters, and having misrepresented the science on the importance of the QuikSCAT satellite on hurricane forecasts, it would be best for Mr. Proenza to step down as director of the National Hurricane Center.

--Jeff Masters

Politics

Updated: 11:03 PM GMT en Octubre 21, 2011

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96L weakens; political storm at NHC

By: JeffMasters, 1:13 PM GMT en Julio 04, 2007

A tropical wave in the mid-Atlantic, near 10N 43W, has lost most of its heavy thunderstorm activity, but could still make a comeback and become a tropical depression by Friday. This system has been labeled "96L" by the NHC. The wave has a small closed circulation, as seen on both visible satellite loops and last night's 4:57pm EDT QuikSCAT pass. Winds from QuikSCAT were as high as 25 mph. This morning's QuikSCAT pass missed the storm. Wind shear is about 10 knots, and is forecast to fluctuate between 5 and 15 knots in the region over the next two days. By Friday, as the system approaches the Lesser Antilles Islands, the GFS model is predicting that wind shear will rise to 20-30 knots, which should tear the system apart. Dry air to the north is limiting the thunderstorm activity of 96L. The Saharan Air Layer (SAL) lies just 50 miles north of the storm's center of circulation, as seen in water vapor satellite loops. None of the reliable computer models develop the system into a tropical depression. Climatologically, formation of a tropical depression in this region of the Atlantic this time of year is quite rare, and I don't think 96L will develop.

In the Pacific, we broke a long spell of over a month without a tropical cyclone, with the formation of Tropical Storm 03W. The cyclone is expected to hit southern China as a weak tropical storm Friday.


Figure 1. Computer model forecast tracks for 96L.

Storm at NHC
Those of you who follow Margie Kieper's View From the Surface blog know that a major political battle is occurring at NHC. Last night, the Miami Herald broke the story that several senior Hurricane Specialists at NHC are now openly calling for NHC chief Bill Proenza's ouster. Margie and I have been quietly gathering information on this brewing story over the past few months, but have not posted anything due to the sensitive nature of the matter. Now that the story has been broken, we can tell you what we know. I will lay out the full details in my next blog, which I plan to post by 1pm EDT today.

Jeff Masters

Politics

Updated: 11:03 PM GMT en Octubre 21, 2011

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A mid-Atlantic tropical wave worth watching; more on this year's steering currents

By: JeffMasters, 1:19 PM GMT en Julio 03, 2007

A tropical wave in the mid-Atlantic, near 9N 38W, has grown more organized since yesterday. This system has been labeled "96L" by the NHC. The wave has a small closed circulation, as seen on both visible satellite loops and this morning's 4:28am EDT QuikSCAT pass. Winds from QuikSCAT were as high as 35 mph. Wind shear is about 10 knots, and is forecast to fluctuate between 10 and 20 knots in the region over the next two days. This is low enough wind shear to allow some slow development. Sea surface temperatures are 27-28 C, which is above the 26 C minimum temperature tropical storms typically need to form. There is one cluster of strong thunderstorms near the center of circulation, but dry air to the north appears to be limiting the thunderstorm activity. The Saharan Air Layer (SAL) lies just 50-100 miles north of the storm's center of circulation, as seen in water vapor satellite loops. The GFS model does indicate a tropical depression might form here, but does not have a very good handle on it, since it is showing far too slow of a forward speed. Our other three reliable models, the NOGAPS, UKMET, and ECMWF, do not develop the system. Climatologically, formation of a tropical depression in this region of the Atlantic this time of year is quite rare. Given this fact, plus the presence of so much dry air near a relatively small circulation, I am not expecting this to become a tropical depression. Movement of 96L will be just north of due west over the next few days at 15 mph, as seen in the model forecast plots (Figure 1).


Figure 1. Computer model forecast tracks for 96L.

More on steering currents for this hurricane season
Yesterday, I posted my bi-monthly hurricane outlook, for the first half of July. Since it was getting a bit long, I presented only a short steering current analysis. More follows here. There are several ways to look at steering currents. I presented the position of the surface high pressure system known as the Bermuda High (or Bermuda-Azores High). Another way is to study how close to the surface a pressure of 500 millibars (mb) is found. When there is low pressure aloft, due to a trough of low pressure, the height at which a pressure of 500 millibars is found moves closer to the surface. If one plots up the "500 mb height anomaly"--the difference of where a pressure of 500 mb is found above the surface, compared to the average height from a climatology of the past 30 years--one gets a good measure of where above or below average storminess occurred. Higher than average 500 mb heights imply less storminess and possible drought conditions. The 500 mb height anomaly plot for June 2007 (Figure 2) shows higher than average heights across the southwestern U.S., where drought and high temperatures were observed in June. Lower than average 500 mb heights imply an above normal preponderance of troughs of low pressure and thus storminess. This was the case over Texas and Oklahoma in June. If these troughs are over the Atlantic, they act to recurve hurricanes out to sea at the longitude they are at. This only occurs if a hurricane penetrates far enough north to "see" the southernmost part of the trough of low pressure. Typically, this happens northward of about 20 degrees north latitude. Figure 2 shows lower than average 500 mb heights occurred over most of the Atlantic, meaning there were many more troughs of low pressure than usual. Had any hurricanes occurred over the Atlantic north of about 20 degrees north latitude, they would have gotten caught up in one of the troughs and recurved out to sea. The latest 2-week forecast from the GFS model shows a continuation of this above average frequency and intensity of troughs of low pressure over the Atlantic--much like we saw in 2006. Thus, we can expect any tropical cyclones that penetrate north of about 20 degrees north latitude to get recurved. This will very likely be the case for 96L, if it ever becomes a tropical storm.


Figure 2. Difference in height (in decameters, or tens of meters) from average of the 500 millibar height above the surface for June 2007. Image credit: NOAA/ESRL.

Jeff Masters

Updated: 1:26 PM GMT en Julio 03, 2007

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First half of July hurricane outlook

By: JeffMasters, 7:45 PM GMT en Julio 02, 2007

The first half of July is usually a quiet period in the Atlantic for tropical cyclone formation. Since 1995, six of 12 years have had a named storm form during the first half of July, giving a historical 50% chance of a first half of July storm. The busiest first half of July occurred in 2005, when three hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. As seen in Figure 1, most of the early July activity occurs in the Gulf of Mexico, Western Caribbean, and Carolina waters. However, a few long-track "Cape Verdes" hurricanes begin to occur. These are spawned by tropical waves that come off the coast of Africa. Tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed July 1-15. North Carolina and the Gulf of Mexico coast from the Florida Panhandle to Texas are the preferred strike locations. Oddly, the Florida Peninsula has been struck by only two storms that formed in the first half of July.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have cooled considerably in the past two weeks over the region we care about the most--the hurricane Main Development Region that extends from the coast of Africa to the coast of Central America, between 10 and 20 latitude. SSTs were about 0.5-1.0 C above average over this region in mid-June, and have now cooled to near normal, when one averages over the entire region. A large region of below-average SSTs has formed between Africa and the Lesser Antilles Islands. Why? African dust storms! Levels of Saharan dust coming off the coast of Africa in June were five times those observed in June 2006, and were the highest observed since at least 1999. All that dust blocks sunlight, preventing the water from heating up as much as usual. One dust storm that was particularly noteworthy exited the African coast June 21-22, and made it to the Caribbean and South America June 25 (Figure 3). However, all that dust also interferes with the accurate measurement of ocean heat energy by satellite, so the SSTs shown here may not be quite as cool as indicated.


Figure 2. Sea Surface Temperature (SST) departure from average for July 1, 2007. Image credit: NOAA.


Figure 3. A huge dust storm moved off the coast of Africa June 21-22, and arrived at the Caribbean on June 25. Image credit: NASA.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 4) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, there is less heat energy available this year than in 2005, which recorded the highest SSTs and TCHP ever measured in the tropical Atlantic. However, this is not true in the Western Caribbean, where we have very high TCHP this year. The African dust storms have not penetrated all the way to the Western Caribbean, and SSTs and TCHP have stayed above average. If we do get an intense hurricane in early July, it will likely be here.


Figure 4. Tropical Cyclone Heat Potential (TCHP) for July 1 2005 (top) and July 1 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart.

Wind shear over the past 11 days (Figure 5, top image) has been above 20 knots along the two branches of the jet stream--the polar jet, which runs along the U.S.-Canadian border, and the subtropical jet, which runs through the Caribbean to North Africa. This is very typical for June, when the jet stream is still very active and quite far south. The jet stream will gradually weaken as summer progresses, bringing lower wind shear and greater chances for tropical storm formation. Shear has been average to above average over nearly the entire North Atlantic during the last half of June(Figure 5, bottom image). The latest two-week forecast from the GFS model predicts that the subtropical jet stream will gradually weaken through mid-July, resulting in lower than average wind shear over much of the tropical Atlantic. This should result in a greater than average chance of a named storm occurring.


Figure 5. Top: Average wind shear over the past 11 days. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation. Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note that wind shear has been above average over most of the tropical Atlantic and Gulf of Mexico over the past 11 days. Image credit: NOAA/CPC.

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa. Despite the fact that the Sahel region of Africa has seen two straight years of above-average rains, which should result in soil stabilization and fewer dust outbreaks, 2007 has seen very high levels of dust coming from Africa. Expect dust from Africa to be a major deterrent to any storms that try to form between Africa and the Lesser Antilles Islands in July.

Steering currents
The steering current pattern for June featured a pattern much like we saw in 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. The position of the Bermuda-Azores High (Figure 6) was pretty close to average. Its strength was only 1 mb below average, driving slightly slower trade winds than average across the tropical Atlantic. I expect this pattern to continue for the first half of July, and the troughs should be frequent enough and strong enough to recurve any tropical storms or hurricanes that penetrate north of the Caribbean Sea. Steering current patterns are not predictable more than about two weeks in advance, and there is no telling if we are in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea. It is encouraging to note that in 2006 the steering current pattern locked into place in late May and stayed that way for almost the entirety of the hurricane season. The atmosphere often stays locked in to a particular steering pattern for an entire summer, and it would not be a surprise if that occurred again this year. If this pattern holds, expect a below-average chance of hurricane landfalls along the U.S. Gulf Coast, and normal to above normal chances along the U.S. East Coast.


Figure 6. Sea level pressure for June 2007 (left), and average sea level pressure from climatology (the years 1979-1995). Note that position and strength of the Bermuda-Azores High during June 2007 was very close to average. Image credit: NOAA/ESRL.

Summary
Recent history suggests a 50% chance of at least one named storm occurring in the first half of July. Wind shear is expected to be below average and SSTs are near average, so I expect a 70% chance of a first half of July named storm this year.

Jeff Masters

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One tropical wave to watch in the mid-Atlantic

By: JeffMasters, 1:51 PM GMT en Julio 02, 2007

A tropical wave that emerged from the coast of Africa late last week is now near 8N 35W, way out in the middle of the Atlantic. This wave has heavy thunderstorm activity and some counterclockwise spin to it, as seen on both visible satellite loops and QuikSCAT. Wind shear is 10-20 knots, and is forecast to fluctuate between 10 and 30 knots in the region over the next two days. Sea surface temperatures are 27-28 C, which is warm enough to support some tropical development. Dry air does not seem to be a hindrance, as the Saharan Air Layer is about 150 miles to the north of the wave. The GFS model does indicate a tropical depression might form here, although our other three reliable models, the NOGAPS, UKMET, and ECMWF, do not. Climatologically, formation of a tropical depression in this region of the Atlantic this time of year is quite rare. Due to this fact, plus the somewhat marginal wind shear and the position of the wave so close to the Equator, I'm not expecting it to develop. However, we should keep an eye on it this week as it moves very slowly to the west at less than 5 mph.



I'll be back this afternoon with my bi-monthly hurricane outlook, for the first half of July.

Jeff Masters

Updated: 2:13 PM GMT en Julio 02, 2007

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All quiet in the Atlantic

By: JeffMasters, 3:22 PM GMT en Julio 01, 2007

Clouds and showers associated with a weak trough of low pressure extend off the east coast of Florida several hundred miles to the northeast. Wind shear has dropped to about 20 knots over this system, so some slow organization is possible over the next day as it moves east-northeast away from the U.S. coast. However, wind shear is expected to increase on Monday over the disturbance, as it approaches the cold front from an extratropical cyclone. The disturbance should merge with the front by Wednesday without developing into a tropical depression. None of the reliable computer models are forecasting tropical storm formation anywhere in the Atlantic over the coming week. Have a great 4th of July holiday week, everyone!

I'll post my July hurricane season outlook early Monday afternoon.

Jeff Masters

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About

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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