Lesser Antilles may see a tropical storm late this week
A concentrated area of intense thunderstorms near 9N 36W, midway between Africa and the Lesser Antilles Islands, has become more organized this morning. NHC has labeled this system Invest 91L, and is giving it a 60% chance of developing into a tropical depression by 8am Tuesday. Wind shear is a moderate 10 - 20 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of 91L to potentially allow further development. The main negatives for development are the current phase of the Madden-Julian Oscillation, which favors downward motion over the tropical Atlantic, and the fact that 91L is too close to the Equator to take much advantage of the Earth's spin to get spinning. Last night's ASCAT pass of the region did show a large region of westerly winds south of 91L, indicating that a surface circulation is trying to form. Satellite imagery shows that the intensity and areal extent of 91L's heavy thunderstorms is increasing. However, there are no signs of a surface circulation, and low-level spiral bands and upper-level outflow are not apparent yet.
Forecast for 91L
There is strong model support for 91L developing into a tropical depression. The GFS, ECMWF, NOGAPS, and UKMET models all develop 91L into a tropical depression by Tuesday or Wednesday. A west to west-northwest motion is predicted, and residents of the Lesser Antilles Islands should anticipate the possibility of a tropical storm arriving in the islands as early as Thursday. It is possible that 91L would pass northeast of the islands, as predicted by the UKMET model, and it is too early to speculate on which of the islands is at most risk. As the storm approaches the Lesser Antilles late this week, 91L will encounter a strong upper-level low pressure system centered north of Puerto Rico. This upper-level low will likely bring high levels of wind shear to the waters just north of Puerto Rico and Hispaniola. Thus, if 91L stays to the south, in the Caribbean, it is far more likely to attain hurricane status than if it pushes north of the Caribbean. As always, long range forecasts of this sort are speculative, and it is too early to reliably say what the long-term risks of 91L becoming a hurricane are. The latest intensity forecast from the SHIPS model shows 91L peaking in strength four days from now, then weakening as it encounters the high wind shear area north of Puerto Rico.
Figure 1. Morning satellite image of Invest 91L.
Next update
I'll have an update Monday morning.
Jeff Masters
Reader Comments
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You may have a future in selling underwater real estate. :)
1) 6,000 posts- That get ridiculous when you are trying to keep up with people, and many times, your obs get lost two pages ago within seconds...
2) The trolls. Now, in years past I would engage them and end up banned myself, which was an exercise in futility. No more of that. I also do not go ape over Invests anymore. Education will do that to ya! I will be on in some capacity when needed.
I notice that the latest SHIPS output has some quite strong shear past 72 hrs, up to 36 kts at 108 hrs. Obviously seeing that upper low north of the eastern Caribbean. Question is - will it really have that much influence on a developing TC. Will it move out of the way? GFS seems to move it out as 91L approaches. But there's a chance it could impart enough shear to weaken 91L/Colin as it nears the islands.
Question is, where will it eventually make its final landfall. I'm thinking somewhere between Tampico, MX and Iceland, presently. Sort of centered along the SE U.S. Coast. Will it cross into the Gulf? Maybe. Models have been indicating a significant weakness in the ridge to the north after it passes around 65W. Will it actually be there? Maybe.
First thing to determine, assuming it develops, is the potential threat to the islands of the NE Caribbean. It's so far south, it's hard to believe that it'll miss the NE Caribbean as many models suggest. Regardless, watch out Bahamas then Florida to the Carolinas, as once it gets away from the upper low it could strengthen quickly. Won't even speculate on final intensity yet, it's still 1600+ miles east of the Caribbean.
Guess I'll be busy the next 10-14 days (and through Thanksgiving).
BY wxman57 Moderator-Pro Met
//www.storm2k.org
Yeah I know KOG i just think it would be easeir to ban his IP again or his new name and then wait a while for him to make another one instead of constantly deleting his posts one by one.
A 2010....nice car....
That I will agree with. The first one of the year is exciting but it starts to wear off after that.
JUst watch the orange ball!
Okay I'll bite what does it say? :)
Thank you sir
Big systems will draw in more dry air from the SAL even before they become named. Large build up of heat could have a negative effect on TC development.
What's the point? He will just come back in under a different name.
I have read you before, you are a respected opinion. I just don't understand the frustration, people are people.....and where this is Dr. Master's Blog, this is a comments section, not a discussion board. I know that others treat it this way....but I do not see where the qualifications of a blog comment section to be "you have to be a qualified forecaster"....
ture i dont think JFV under stans what the word BANNED means
18z Early Cycle NHC model tracks
Invest91
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)
Dynamic Models (More sophisticated models)
Proud mincaster right here! ;)
Anyways, 91L wasn't declared... and I can see why. I have to admit I jumped the gun on this one. It will, however, have the organization needed to be declared by the 11 pm EDT advisory, 5 am EDT at the latest. Then, the real fun begins...
This is a definate east coast storm. Everyone start preparing on the East Coast!
He will have ample competition being in South Florida...
AFDHGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
240 PM CDT SUN AUG 1 2010
.DISCUSSION...
UPPER LEVEL RIDGE OVER TEXAS WILL KEEP HOT CONDITIONS IN PLACE
THROUGH THE NEXT 5-7 DAYS. HUMIDITY WILL POSSIBLY BE HIGHER
STARTING TOMORROW THROUGH WEDNESDAY SO WILL HAVE TO MONITOR FOR
HEAT ADVISORY CONDITIONS. THE RIDGE MAY FLATTEN SOME TOWARDS THE
WEEKEND SO WILL SHAVE A DEGREE OR TWO OFF MAX TEMPS FROM EARLIER
IN THE WEEK AND KEEP SLIGHT CHANCE OF THUNDERSTORMS FRI-SUN.
TROPICS MAY DECIDE TO ACT UP WITH AN ORGANIZING SYSTEM IN THE
ATLANTIC. LONG RANGE MODELS BRING THIS SYSTEM TOWARDS SE U.S. BY
NEXT WEEKEND.
I've seen no evidence of "a well-defined closed surface circulation with organized convection."
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