Lesser Antilles may see a tropical storm late this week

By: Dr. Jeff Masters , 1:51 PM GMT on August 01, 2010

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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

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Wasn't it 2007 that we had quite a few storms develop in the same area and head straight to mexico on a straight path? A few storms hit Jamaica that year too, but the point is that most stayed south. How would I go about looking up the data from that year (looking at steering) and comparing it to this year? Thnx
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laughs

Quoting nash28:
Oh boy...

Let the fighting begin. And many wonder why I only observe here anymore.. This thing is over a week away from the US and already the bickering begins on landfall.

It is STILL fighting the ITCZ. We don't even have a closed low yet. Take a pill. Enough of the "it's gonna hit here, cause I want it to hit here to feel important" forecasts. Pay attention to those folks here who know what they are doing...

Weatherguy03
StormW
Levi
Drakoen
Weather456

I would include myself in the list, but I really have no interest in posting obs here much anymore because of all of the infantile nonsense.

When and if things get sticky, I'll do that on my own blog.
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it is a long way out....but I'd believe the patterns of the ECMWF, which have performed better recently on track, than those of the GFS or HWRF which have had a poleward bias to every storm this year, and are again, wanted to push this storm east, or up the east coast. It is a possibility though....long way to go.

Quoting btwntx08:
hmmm ecmwf 12z at 240 hr
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1572. nash28
Oh boy...

Let the fighting begin. And many wonder why I only observe here anymore.. This thing is over a week away from the US and already the bickering begins on landfall.

It is STILL fighting the ITCZ. Take a pill. Enough of the "it's gonna hit here, cause I want it to hit here to feel important" forecasts. Pay attention to those folks here who know what they are doing...

Weatherguy03
StormW
Levi
Drakoen
Weather456

I would include myself in the list, but I really have no interest in posting obs here much anymore because of all of the infantile nonsense.

When and if things get sticky, I'll do that on my own blog.
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1571. ssmate
Quoting FLdewey:
I think it's going somewhere west of where it is now for certain.
Are you kidding? Nothing is certain right now.
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Quoting bappit:

It is still disorganized. That's why it is not upgraded.
What are you looking at? 91L has a well-defined closed surface circulation with organized convection. Satellite estimates also are worthy of tropical depression classification.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1568. GBguy88
We hit 104 degrees in Pensacola today. Sitting at 102 right now. Good grief.
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1566. bappit
Quoting Levi32:


Greatest 850mb vorticity is not under the convection on the right. CIMSS maps can be wrong when low-level clouds cannot be observed well by satellite. They fill in with numerical model data and it becomes unreliable. The CIMSS maps don't even agree with themselves sometimes.

Observe....the "Regular" 18z vort map:



And the rapid-scan one for 18z:



See the difference?

The "regular" map is more accurate in this case. The highest vorticity on that map is closer to the western area of convection and is near 11.5N, 35W on the CIMSS map, which may still be a little too far east, but it's better than the map you're looking at.

The ascat confirmed the location of max vorticity.
Member Since: May 18, 2006 Posts: 10 Comments: 6157
1565. fire635
Quoting bwt1982:
Really worried for Bermuda with this storm! We lucked out here in Florida again! Whoop whoop!


Its a little early to write off anything..no?
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1564. bwt1982
Quoting TexasHurricane:
So, I guess we may have a East coat or fish strom.....



Dont say the dreaded F word on here...The wishcasters hate fish storms. With that being said I do agree that that is a fish storm or headed to Bermuda possibly. That was my thinking all along and the models are starting to verify that!
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1561. Levi32
A repost:

Tropical Tidbit for Sunday, August 1st, with Video

Back later.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
You are right...I should just shake my head and move on...

Quoting CaneBeast2010:


brah, just ignore him
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Quoting ironbark:
the models are all over the place.its a safe bet to say anybody from georgia to south texas should monitor the developing storm.


....

Further NORTH of Georgia should monitor this system. I think it's all clear from the GOMEX, IMHO.
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dont turst any mode runs in tell the storm is at 55W
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
1557. Relix
Looking impressive to be honest. Definitely a TD at this point. I am quite confident in the model consensus of it going north of PR so I am honestly not that worried at all about the system here. Might leave some rains and of course lots of heat. To pinpoint my island is a feat only a few hurricanes every decade or so can make haha. As I said, confident, but watchful. Especially since it's getting stronger than anticipated a more WNW course is expected.
Member Since: August 3, 2006 Posts: 0 Comments: 2741
Quoting portcharlotte:
Disagree politely...You will see many bahamian cruisers this year unless you are in the caribbean and are a wishcaster! The Bermuda High's position (mean position) will allow more wnw courses this year. Many forecasters have pointed this out. Bonnie already gave us a hint.


No problem, just my opinion or you have yours, no wishcasting on my part. I had my taste and more of what destructive hurricanes can do, just watch, wait and see, we'll find who's right or wrong soon enough!
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1554. KEEPEROFTHEGATE (Mod)
X
Member Since: July 15, 2006 Posts: 178 Comments: 56059
1551. LBU1
Quoting bwt1982:
Really worried for Bermuda with this storm! We lucked out here in Florida again! Whoop whoop!


Really!
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Quoting bwt1982:
Really worried for Bermuda with this storm! We lucked out here in Florida again! Whoop whoop!
I am really worried about your thought process...there is no "all clear" for anybody, anywhere as of yet.
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Are you kidding....how many days out are we? NO WHERE in the Western Atlantic basin is safe from anything yet....

Quoting bwt1982:
Really worried for Bermuda with this storm! We lucked out here in Florida again! Whoop whoop!
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Quoting CaneBeast2010:


Wrong, dead WRONG, as a matter of fact. The ridge will keep Bermuda safe,s orry, but, this will nnot be another 09, wishcastetrs



you are dead wrong in face you dont even no what your talking about
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
The long-range track and intensity forecasts remain highly uncertain.
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1544. KEEPEROFTHEGATE (Mod)
0XX/INV/91L
MARK
10.23N/36.73W
Member Since: July 15, 2006 Posts: 178 Comments: 56059
Quoting MississippiWx:
With the exception of Bonnie, it seems like our systems want to be big this year. We can most likely attribute that to the large build up of heat in the Atlantic.
what other systems, 95L ? ...now she was a monster :)
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the models are all over the place.its a safe bet to say anybody from georgia to south texas should monitor the developing storm.
Member Since: Posts: Comments:
Disagree politely...You will see many bahamian cruisers this year unless you are in the caribbean and are a wishcaster! The Bermuda High's position (mean position) will allow more wnw courses this year. Many forecasters have pointed this out. Bonnie already gave us a hint.


Quoting stormpetrol:

Imo this will be a Caribbean Cruiser, the majority of storms that form at that lattitude seldom go north of Cuba , this storm imo opinion will take similar tracks that Ivan 04, Dean 07 or Emily 2005 or just split the difference, of course it could still move more wnw/nw , I just don't see it.
Member Since: September 7, 2008 Posts: 0 Comments: 703
I still say we could see a renumber at any time.
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1538. bwt1982
Really worried for Bermuda with this storm! We lucked out here in Florida again! Whoop whoop!
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Quoting leo305:


ANDREW HIT SOUTH OF MIAMI, AND THEN HIT NEW ORLEANS

KATRINA HIT NEAR MIAMI AND THEN HIT NEW ORLEANS!

yes I agree =P
Andrew's Louisiana's landfall was just west of Morgan City, not NOLA.
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1534. Ossqss
click to enlarge



Member Since: June 12, 2005 Posts: 6 Comments: 8188
1532. KEEPEROFTHEGATE (Mod)
Quoting MississippiWx:
With the exception of Bonnie, it seems like our systems want to be big this year. We can most likely attribute that to the large build up of heat in the Atlantic.

more to the picture than meets the eye
when it comes to the effect of high SST's
increased vapour levels
wider reaching warm tropical converenge zones
warm water temps far reaching into the northern areas of ocean
this is more than likly the next area of reaction
all these things are a road to the unknown
there effects never before experienced
Member Since: July 15, 2006 Posts: 178 Comments: 56059
The original wave axis is trying to take over.

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So, I guess we may have a East coat or fish strom.....

Member Since: July 2, 2009 Posts: 0 Comments: 2811
1529. Levi32
Quoting StormW:


Well, La Nina and the PDO are two different entities.


Though, La Nina is a very big part of the PDO. The PDO is just the larger version of the ENSO that includes stuff in the mid-latitudes and has a bigger time-scale. You will rarely see a solidly cold PDO without a La Nina in the equatorial Pacific.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting P451:


I don't know...Shear seems awfully high in it's path. Dry air could also be a problem as it gains latitude.

It looks to be in a healthy place right now but once it nears PR, unless something changes, it won't be by then.

Imo this will be a Caribbean Cruiser, the majority of storms that form at that lattitude seldom go north of Cuba , this storm imo opinion will take similar tracks that Ivan 04, Dean 07 or Emily 2005 or just split the difference, of course it could still move more wnw/nw , I just don't see it.
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Quoting MiamiHurricanes09:
No renumber yet; no tropical depression at 5PM EDT. Now I'm out.


Interesting to note, there was never and still isn't a renumber from 97L (Bonnie)
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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