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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I think 91L (Colin?) could take a track similar to Georges 1998, but slower at intensifying and a bit farther north.

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What are the update times today? I've gotten all confused (go figure) ---
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.
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Quoting MiamiHurricanes09:
Satellite presentation is good enough for it to be classified, now let's see if it can close off its circulation.


The circulation is closed. It is just broad. Also the ASCAT pass suggest the system may be located closer to 10.5N

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Funny how whenI state that S. FL needs to pay close attention to this I get bashed. But when model runs and other bloggers tend to have the same opinion then noone says a word...GO FIGURE!
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Hey Drak How's It.

I was looking at some things and am leaning towards this being for skirt event for the Lessers and an Issue for Bermuda. Seems to me there will be an escape hatch open up in about day 5. Thoughts
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91L still does not have a well-defined center. It's gonna need to tighten up.
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Quoting CybrTeddy:
SAB at 1.5
TAFB at 2.0
Satellite presentation is good enough for it to be classified, now let's see if it can better define its center and also consolidate it.
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I see it has a well defined circulation, and the thunderstorms are at the center. Looks like a Cape Verde to me!

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To what longitude are the hurricane hunters allowed to fly (55W?). I don't remember.
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Quoting Drakoen:
Good morning everyone!
Good morning Drak!
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SAB at 1.5
TAFB at 2.0
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Quoting Drakoen:
Looks like 91L is on its way to becoming a tropical depression. Microwave imagery shows the poleward banding wrapping in cyclonically towards the 1007mb low pressure center located near 10N 36.3W. While upper level winds are currently 10-20 knots an upper level high is located to the northwest of the center of circulation. My forecast is for the system to heading WNW in the general direction of the northern Lesser Antilles in best agreement with the ECMWF and the GFS models.

Hello Drak.
Member Since: July 7, 2010 Posts: 0 Comments: 5690
Nice summary Sebastian
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Quoting alaina1085:

I live a few hours inland in SELA so by the time a cat 3 gets to me its down graded. So I dont have to worry about evacuating. But yea if I lived near the coast I wouldnt take any chances.


I might stay for a 3 but for a 4 or 5 I'll be outta here.
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Good morning everyone!
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Quoting alaina1085:

Hence why I said most :) I know there are those out there that genuinely dont want a cane.
You have it backwards. Most people with a descent level of intelligence do NOT want to be hit by a hurricane. Only a few of the clueless want to get samcked by a major. Give people a little more credit.
Member Since: August 22, 2008 Posts: 0 Comments: 755
Quoting scott39:
Do some bloggers on here really want a Hurricane to hit them???????

Do some tornado chasers want to be within 5-10 miles of a tornado?
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting Weather456:


There will be disagreements because of the broadness of 91L's center. From my visible obs, its near 10N35W from my last update, which was using sat images from early this morning.


Just had a look at the floater and I think your dead on, thanks!
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Quoting sebastianflorida:
If the system remains weaker, it may go further south into the Caribbean or over most of the islands and get torn up over Hispaniola. If it strengthens or forms earlier the more northerly situation is likely. Atmospheric conditions are very favorable for the latter.

What are the odds favoring now? Strengthening and the more northerly route. Although shear will increase as it gets closer to the islands which likely will keep it from being too strong until past the northeastern Caribbean.

Since the odds are more favorable for the northerly route, a key to the future track may be the presence of two upper ridges, one west of Bermuda and another over the southern plain states. If a weakness exists offshore the Carolinas, that would be what drags the wave more northerly, and if it barely misses the northeastern Caribbean, would be the cause. What's not happening there would likely be enough to continue to pull it out to sea. What happens after that is the weakness gets plugged, which completes the ridge and generally drags it more westward, which is why those in Florida would want to watch it. Chances for a gulf impact without Florida are low currently, but not non-existent. .

It will take until it develops and trends over the next few days to up the odds in any particular situation though. It is still very early, and nothing has developed yet. However it is August now, and historically this is the time to be very careful about systems such as these.

Who will need to watch the system over the next week or so if it does develop? Northeastern Caribbean. Bahamas, Florida (particularly east central and south Florida), and the southeast Coast up to the Carolinas. The good news is that shear closer toward the Caribbean goes up, which will likely keep the system from getting too strong.

When? (Estimates can change if the forward motion of the system changes)
If it affects Northeast Caribbean?, for them Wednesday/Thursday
If it affects Bahamas? Saturday
If it affects Florida/East Coast? Sunday/Monday (next week)
I know they always say stronger further north and weaker further south and people seem like they don't want you to use Ivan as an example but when Ivan was in this area he was already a TS (04 / 0000 9.1 35.0 999 45) and did not track "further" north. As a matter of fact, he stayed pretty far south until entering the Caribbean.
Member Since: October 9, 2008 Posts: 0 Comments: 8392
Quoting scott39:
Do some bloggers on here really want a Hurricane to hit them???????


OZ........... LOL
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Quoting WeatherNerdPR:

Nice. TD by 5PM?
Not until it closes off its area of low pressure, but that could happen very soon. What we have is great satellite presentation.
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Quoting alaina1085:

Hes just brave enough to say what most other floridians want but wont admit LOL.


Thank you.
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Here's a dry air loop. Freeze it on the last frame and it shows a gap in the SAL around the invest.

Looking at the big picture also puts the invest in perspective a bit. It is way out there right now. I suspect that the big chunk of clouds south of 10 north and west of the invest location is not part of the invest.
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Do some bloggers on here really want a Hurricane to hit them???????
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249. Relix
So the ECMWF and Drakoen expect me to hunker down in PR. Ok, I'll listen. =P
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Quoting Drakoen:
Looks like 91L is on its way to becoming a tropical depression. Microwave imagery shows the poleward banding wrapping in cyclonically towards the 1007mb low pressure center located near 10N 36.3W. While upper level winds are currently 10-20 knots an upper level high is located to the northwest of the center of circulation. My forecast is for the system to heading WNW in the general direction of the northern Lesser Antilles in best agreement with the ECMWF and the GFS models.

Thanks for your input Drake
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting MiamiHurricanes09:
TAFB at T2.0. That would be good enough for 91L to be classified as a tropical depression. Looking at satellite it really doesn't look raged to me.

TAFB, MF, VI, 5, , , , MET8, CSC, , DT = 2.0 BASED ON 0.3 BANDING WITH (T 0.5) WHITE B

Nice. TD by 5PM?
Member Since: July 7, 2010 Posts: 0 Comments: 5690
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Quoting Drakoen:
Looks like 91L is on its way to becoming a tropical depression. Microwave imagery shows the poleward banding wrapping in cyclonically towards the 1007mb low pressure center located near 10N 36.3W. While upper level winds are currently 10-20 knots an upper level high is located to the northwest of the center of circulation. My forecast is for the system to heading WNW in the general direction of the northern Lesser Antilles in best agreement with the ECMWF and the GFS models.


Good morning Drak!
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Looks like 91L is on its way to becoming a tropical depression. Microwave imagery shows the poleward banding wrapping in cyclonically towards the 1007mb low pressure center located near 10N 36.3W. While upper level winds are currently 10-20 knots an upper level high is located to the northwest of the center of circulation. My forecast is for the system to heading WNW in the general direction of the northern Lesser Antilles in best agreement with the ECMWF and the GFS models.
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It will be interesting to see Bahahurricaneman's reaction to the new invest.
Looks like he's in the center of the cone of uncertainty at present, though it is still several days away.
Member Since: July 11, 2006 Posts: 14 Comments: 11351
Quoting truecajun:


so if 91 strengthens quickly it will go towards low near pr and experience shearing, but if it wanes in strengthening, it will travel more south of that low and not into the shear?? I'm asking not stating

I'm bumping my post for answer. Maybe bad question since obviously strengthening?
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It is so dry and hot here in FL ...we need something tropical (East Coast Central)...I don't want the fires again..

did my pic come up? test
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Quoting divdog:
Well I am a floridian who has been thru 4 major hurricanes and you can put me in the no florida hurricane camp. We are not all 20 years old wishing to see our town destroyed. Don't put us all in the florida wishcasters association like jeff.

Hence why I said most :) I know there are those out there that genuinely dont want a cane.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting hurricaneben:


Well I wish we in FL get hit. We haven't had a hurricane since 2005's Wilma.


Who in their right mind would wish this?
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Quoting Hurricanes12:
What scares me the most is that if this is another S.FL storm, people will think it's going to be another Bonnie and won't listen to the authorities. During Bonnie the local news went crazy. It's early in the game with this system but it could be a disastrous situation.


i agree with you...miami thinks that they had had their hurrucane for the year. in 2005 we had katrina, rita and wilma...we need to be very calm until 5 days ahead od time....
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Quoting sammywammybamy:




An Hebert Box (pronounced AY-bear, also known as Hebert's Box) is one of two regions of the tropical Atlantic Ocean that are useful as predictors of hurricanes that will strike South Florida, USA. They are named for former National Weather Service and National Hurricane Center forecaster Paul Hebert, who observed in the late 1970s that most strong hurricanes (characterized as those with winds exceeding 110 miles per hour (177 km/h)) which had struck South Florida since 1900 had also passed through one of these two small 335-mile-by-335-mile (517-km-by-517-km) square geographic regions.[1]

Examples include unnamed hurricanes in 1926, 1928, 1933, and 1935, as well as the major hurricanes Donna and Betsy, all of which came through a Hebert Box. Collectively these storms killed more than 2,000 people in Florida. Conversely, storms such as the major hurricanes Floyd and Gert in 1999, which both were headed for Florida at one point, missed the Hebert Boxes and turned away from Florida at the last minute.[1]





The first Hebert Box is located east of Puerto Rico over the US Virgin Islands, between 15° and 20° north latitude and 60° to 65° west longitude. This was the first area that Hebert discovered, and provides an indication for the behavior of Cape Verde type storms, which form off of the western coast of Africa near the islands of the same name. This first box is useful for storms that typically form in the early part of the Atlantic hurricane season (June through early September).

The second Hebert Box is located over the Cayman Islands between 15° and 20° north latitude and 80° to 85° west longitude. This was the second discovered, and provides an indication for the behavior of storms that will move north to hit Florida. These are usually late-season storms that form in this region in late September and October, and this box is mostly concerned with them.[2]


I always wondered what those boxes were...
Member Since: July 7, 2010 Posts: 0 Comments: 5690
Quoting alaina1085:

Hes just brave enough to say what most other floridians want but wont admit LOL.
Well I am a floridian who has been thru 4 major hurricanes and you can put me in the no florida hurricane camp. We are not all 20 years old wishing to see our town destroyed. Don't put us all in the florida wishcasters association like jeff.
Member Since: August 22, 2008 Posts: 0 Comments: 755
Quoting MiamiHurricanes09:
LOL! I've got to admit I did like Bonnie, a nice peaceful rain and nothing more. But when we start with those Cat 1's and Cat 2's I'm out...! LOL.

I live a few hours inland in SELA so by the time a cat 3 gets to me its down graded. So I dont have to worry about evacuating. But yea if I lived near the coast I wouldnt take any chances.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
This system is so far out at the moment, that it could end up anywhere from the Caribbean to the Gulf or East Coast if it develops....Things will change with the models as conditions change over the next several days and the models get fed better data from recon and Gulfstream flights......As usual for approaching CV systems, the immediate threat is for the Antilles and that's as far as we should be going at the moment.
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Quoting alaina1085:

Hes just brave enough to say what most other floridians want but wont admit LOL.
LOL! I've got to admit I did like Bonnie, a nice peaceful rain and nothing more. But when we start with those Cat 1's and Cat 2's I'm out...! LOL.
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If the system remains weaker, it may go further south into the Caribbean or over most of the islands and get torn up over Hispaniola. If it strengthens or forms earlier the more northerly situation is likely. Atmospheric conditions are very favorable for the latter.

What are the odds favoring now? Strengthening and the more northerly route. Although shear will increase as it gets closer to the islands which likely will keep it from being too strong until past the northeastern Caribbean.

Since the odds are more favorable for the northerly route, a key to the future track may be the presence of two upper ridges, one west of Bermuda and another over the southern plain states. If a weakness exists offshore the Carolinas, that would be what drags the wave more northerly, and if it barely misses the northeastern Caribbean, would be the cause. What's not happening there would likely be enough to continue to pull it out to sea. What happens after that is the weakness gets plugged, which completes the ridge and generally drags it more westward, which is why those in Florida would want to watch it. Chances for a gulf impact without Florida are low currently, but not non-existent. .

It will take until it develops and trends over the next few days to up the odds in any particular situation though. It is still very early, and nothing has developed yet. However it is August now, and historically this is the time to be very careful about systems such as these.

Who will need to watch the system over the next week or so if it does develop? Northeastern Caribbean. Bahamas, Florida (particularly east central and south Florida), and the southeast Coast up to the Carolinas. The good news is that shear closer toward the Caribbean goes up, which will likely keep the system from getting too strong.

When? (Estimates can change if the forward motion of the system changes)
If it affects Northeast Caribbean?, for them Wednesday/Thursday
If it affects Bahamas? Saturday
If it affects Florida/East Coast? Sunday/Monday (next week)
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Quoting Weather456:


There will be disagreements because of the broadness of 91L's center. From my visible obs, its near 10N35W from my last update, which was using sat images from early this morning.

It has no clearly defined center yet.

And if you are playing invest bingo at home, check your card and fill in that square!
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Quoting sammywammybamy:


lol. ur silly.

Hes just brave enough to say what most other floridians want but wont admit LOL.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
HunkerDown, Do you have a short or long range forecast on 91L to post?
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TAFB at T2.0. That would be good enough for 91L to be classified as a tropical depression. Looking at satellite it really doesn't look raged to me.

TAFB, MF, VI, 5, , , , MET8, CSC, , DT = 2.0 BASED ON 0.3 BANDING WITH (T 0.5) WHITE B
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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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