Remainder of July hurricane outlook
Not much has changed in the Atlantic since my early July Atlantic hurricane outlook posted two weeks ago. Tropical cyclone activity typically picks up a bit during the last half of July, but we are still a month away from when hurricane season really gets going. Since the current active hurricane period began in 1995, nine of 14 years (63%) have had a named storm form during the last half of July. We had two last-half-of-July named storms last year--Christobal and Dolly. As seen in Figure 1, most of the late 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 1851 - 2006 that formed July 16 - 31.The Gulf of Mexico coast is the preferred strike location. There are still very few major Cape Verdes-type hurricanes forming in the last half of July.
Sea Surface Temperatures
Sea Surface Temperature (SST) anomalies have warmed slightly over the past two weeks, and are about 0.3°C (0.5°F) above average over the tropical Atlantic between Africa and Central America (Figure 2). These are some of the coolest SST anomalies for this time of year that we've seen since 1994. The strength of the Azores-Bermuda high has been near or slightly below average over the past two weeks, driving slightly below average trade winds. Weaker trade winds don't mix up as much cold water from the depths, and cause less evaporative cooling. The latest 2-week run of the GFS model predicts continued near-average or slightly below average-strength trade winds through the end of July, so SSTs should remain slightly above average during this period.
Figure 2. Sea Surface Temperature (SST) departure from average for July 13, 2009. SSTs were about 0.3°C (0.5°F) average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS
El Niño
El Niño conditions continue to amplify over the tropical Eastern Pacific. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", are now 0.4°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology (Figure 3). An increase of another 0.1°C will push the current El Niño into the "moderate" category. NOAA's Climate Prediction Center issued an El Niño Advisory earlier this month. The latest set of mid-June runs of the El Niño computer models are almost universally calling for El Niño conditions to become well-established for the peak months of hurricane season, August - October. It is likely that Atlantic hurricane activity will be suppressed in 2009 due to the strong upper-level winds and resulting wind shear an El Niño event usually brings to the tropical Atlantic.
Figure 3. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 8, 2009, SSTs in the Niño 3.4 region had risen to 0.9°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: Australian Bureau of Meteorology.
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. The jet stream's band of strong high-altitude winds is the main source of wind shear in July over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.
The jet stream over the past three months has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England.
The jet stream is forecast to maintain this two-branch pattern for the next week. However, during the final week of July, the subtropical jet is forecast to weaken. This will leave regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July (Figure 4), increasing the chances of hurricane development.
Figure 4. Wind shear in m/s between 200 mb and 850 mb on July 31, 2009, as forecast by the 00Z July 15, 2009 run of the GFS model. The subtropical jet is forecast to weaken by this time, leaving regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.
Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past month. 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. Several well-developed African waves have been done in by dry air from Africa over the past few weeks.
Steering currents
The steering current pattern over the past few weeks has not changed much. A persistent trough of low pressure has remained entrenched over the Eastern U.S. all summer, bringing cool and relatively moist weather to the eastern half of the country. This trough is strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the strong trough over the Eastern U.S., which decreases the hurricane risk to the U.S. Gulf Coast. There is no telling what might happen to the steering current pattern during the peak months of August, September, and October, but it is often difficult to break a months-long steering current pattern like the current one.
Summary
Recent history suggests a 63% chance of a named storm occurring in the last half of July. Given that none of the computer models are forecasting tropical storm formation in the coming seven days, and SST and wind shear patterns look pretty average, I'll go with a 30% chance of a named storm forming this month. Such a storm would most likely form near the end of the month, when wind shear is expected to decline due to a weakening of the subtropical jet stream. The last time we went this long in the season without a named storm forming was in 2004, when the first storm (Alex) formed on August 1.
I'll have a new post on Friday.
Jeff Masters
Reader Comments
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 — Blog Index
This is why you are ignored all the time by people!
What deserves! The CMC....LOL
Did you read the bottom half of my Update....if not read it again!
I think the GFS has done that more this year...
Maybe next season I will keep track of how many phantom storms the two spin up over the season.
enjoy have fun
the wave at 30w looks much better thanks the 50 west i think that one might have a better chance is it the 50 w one that suppose to effect fla or both
No, last year it was almost the gospel of cyclonegenesis. Arthur, Bertha, Cristobal, Eduoard, Fay, Gustav, Hanna, Ike, Kyle, a week or more in advance were all caught by the consistancy of the GFS.
The CMC is not really good at intensity, but it is great for tracking eversince last year.
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT THU JUL 16 2009
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS.
$$
FORECASTER BRENNAN
Nuttin'
And how many ghost storms did it spin up, especially before the season got rolling?
All I am saying is that models more than 3 days out (5 days in a stretch) are not something to rely on. Personally, until 2-3 models are fully on board, and its less than 5 days out, (3 days before the models prove themselves for reliability), I don't pay much attention to the models for anything smaller than synoptic scale.
When you write things like that you just leave yourself open for ridicule. There's nothing wrong with what you said, but at least try to make your comments have the correct spelling. It's very easy to attack someone who doesn't seem to have a firm grasp on the english language.
http://www.ssd.noaa.gov/goes/east/catl/rb-l.jpg
Ramsdis close up floater
http://hadar.cira.colostate.edu/ramsdis/online/trop_ge_storm_relative_1.html
However, it will enter very hostile conditions with high wind shear and some dust.
Not alot actually. I don't know whats the GFS problem this year.
A TROPICAL WAVE IS ALONG 31W S OF 18N MOVING W AT 15 KT. RECENT
SATELLITE IMAGERY DEPICTS A LOW TO MIDDLE LEVEL CYCLONIC
CIRCULATION ALONG THE WAVE AXIS NEAR 10N. AN EARLIER ASCAT PASS
AROUND 1150 UTC ALSO CAPTURED A BROAD LOW-LEVEL CIRCULATION NEAR
10N WHICH REMAINS EMBEDDED WITHIN THE ITCZ AXIS. SCATTERED
MODERATE CONVECTION IS FROM 6N-13N BETWEEN 27W-33W.
yup
On the down side, however, is the damage (among many other factors in this complex world)it is alleged to be causing to the Coral Reef structures in the Caribbean.
Meanwhile, I welcome the "boring" quiet that exists for the time being in the region!
Yup and about the C.V wave they develop it to a tropical wave.
IMHO, the problem with many of the "thoughts/experiments" etc out there, is the sometimes apparent lack of holistic "cradle to grave" investigation into the full ramifications of what we may be embarking on.
For instance - in this case - what will happen to the whole ocean structure - currents, life, atmospherics etc if we start "sucking up" huge quantities of cold water from the depths to the surface.
Long live the ingenuity, enquiry and humane capabilities of humankind - but be thorough before commencing any real life applications - please.
I think before we ever even try to master mother nature (a false hope in my opinion), we need to fully understand her - it is patently obvious that we do not.
Hi Storm...
Not joking - USA today article - choked on my coffee and sprayed it all over the page. The word "tunnel" wasn't mentioned but hey....great minds and all (grin)....
Viewing: 701 - 751
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 — Blog Index