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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Yeah dragonfly that same lightning show was over here near me today daytona and to the south in edgewater where I live. It was a awesome light show huge branch lightning bolts and very bright blues and whites now hollywood is getting it, sorry I didn't mean to wave my wand haha. So how did day go hollywood? Oh btw my name is nick and yes my heritage is german.
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To be quite honest, I am surprised that 91L is not a tropical depression yet. I'd presume it will be one at 5:00 am, though.
Member Since: June 29, 2009 Posts: 13 Comments: 5238
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Quoting GeoffreyWPB:
For God's sake SSIG...put...ahhh never mind. :) Time to retire that line!


If he needs a shirt, I suggest the Guy Harvey "Save Our Gulf" series.
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2921. Drakoen
Quoting bappit:
Okay, I took a screen shot of the last frame of the MIMIC gif.



This shows the pouch 91L can develop in. The vectors apparently are calculated from how the pixels change as the images morph. The center of the pouch would have zero velocity. The vector there is represented as a dot.

The dot seems to be located at about 36.8, 11.5! I misread the graticule earlier while it was animated. I think ideally it would be at the center of the MIMIC image, so this kind of estimating may be imprecise. (Really?)


Thanks for that 11.9N 36.9W
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Quoting StormW:
The weakness in the ridge has shifted west slightly:

03Z AUG 01


00Z AUG 02

Does that mean that the models might shift more towards the islands?
Member Since: July 21, 2010 Posts: 60 Comments: 1011
2919. Patrap
91L is a bad seed.

Has BAD all over it..

If it can be all it poses downstream.

And that High is gonna be a friend fo some,,and the nose of it a nightmare for somebody in a week.
Member Since: July 3, 2005 Posts: 414 Comments: 125613
Quoting ho77yw00d:


seriously? wow well your blessed to be alive!!! my butt is staying inside!!

I was dead for about 2 mins before my mum resuscitated me.
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It won't let me post the pic,but the navy has a pretty cool night visible sat!!!!
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting AussieStorm:

I think i was bit more fortunate then him,,, I have few reminders of being stuck other than a weird feeling when a storm is in the area and a scare on my hand. He had a disc removed from his back.


My father in law once saw a foursome struck on the golf course ahead of him on the same hole. I won't describe what he told me but suffice it to say that on the first sign of trouble I head indoors quickly.
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Quoting ho77yw00d:


seriously? wow well your blessed to be alive!!! my butt is staying inside!!


Yeah please, lightning is the #1 weather related killer in the state of FL. Wind just picked up quite a bit.
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2914. bappit
Okay, I took a screen shot of the last frame of the MIMIC gif.



This shows the pouch 91L can develop in. The vectors apparently are calculated from how the pixels change as the images morph. The center of the pouch would have zero velocity. The vector there is represented as a dot.

The dot seems to be located at about 36.8, 11.5! I misread the graticule earlier while it was animated. I think ideally it would be at the center of the MIMIC image, so this kind of estimating may be imprecise. (Really?)
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Quoting AussieStorm:

oh, don't go out,,, I can tell you know, it's not worth getting stuck just for the sake of a photo. I am a survivor of being struck.


seriously? wow well your blessed to be alive!!! my butt is staying inside!!
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Quoting Drakoen:
MIMIC-TPW clearly shows a circulation above 10N

Seems to be around 12N, Microwave also suggests that the center be by 12N.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Quoting stillwaiting:
I wonder how far away we are from .......TD04 has formed!!!,lol...like 20minutes IMO....


Nah. Probably 5 AM.
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Quoting kmanislander:


You and Lee Trevino !

I think i was bit more fortunate then him,,, I have few reminders of being stuck other than a weird feeling when a storm is in the area and a scare on my hand. He had a disc removed from his back.
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As the Pot(tery) Boils... the saga :)

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Quoting extreme236:


I'd almost guarantee a TD at 5am with the info I'm seeing.
Still has to work on a few things, but TD at 5AM EDT seems very likely to me.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
2907. Drakoen
MIMIC-TPW clearly shows a circulation above 10N

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2906. pottery
Quoting Orcasystems:


I will keep you updated :)
Thats what friends are for.

You are a True Friend, Orc.
You always let me know when Bad Stuff is a-commin'.
heheheheh
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2807 MyrtleCanes " [track map of HurricaneBonnie] "

The model projections more closely overlap

but frankly I put little trust in track predictions based on what is still an Invest.
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Quoting extreme236:


I'd almost guarantee a TD at 5am with the info I'm seeing.


11 am seems likely. JMO
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2903. Levi32
Quoting Relix:


I said I would leave but.. well... this is addicting =P.

What change in track do you think this could create?


None, this was expected, but it may be messing up some of the model runs.
Member Since: November 24, 2005 Posts: 628 Comments: 26455
I wonder how far away we are from .......TD04 has formed!!!,lol...like 20minutes IMO....
Member Since: October 5, 2007 Posts: 20 Comments: 4970
2901. KEEPEROFTHEGATE (Mod)
here is another one an IR image for ya pott
Member Since: July 15, 2006 Posts: 165 Comments: 52262
For God's sake SSIG...put...ahhh never mind. :) Time to retire that line!
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hey cacios
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Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting cirrocumulus:
10.2N, 37.5W

is this wrong or right??
Link
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Quoting Patrap:
Record Report

Statement as of 04:40 PM CDT on August 1, 2010

... Record high temperature set at New Orleans...

a record high temperature of 100 degrees was set at New Orleans
International Airport today. This breaks the old record of 97 set in
1998.


... Record high temperature set at Baton Rouge ASOS...

a record high temperature of 99 degrees was set at Baton Rouge today.
This breaks the old record of 98 set in 1998.



... Record high temperature tied at Gulfport ASOS...

a record high temperature of 101 degrees was tied at Gulfport today.
This ties the old record of 101 set in 1986.



... Record high temperature set at Slidell ASOS...

a record high temperature of 100 degrees was set at Slidell today.
This breaks the old record of 98 set in 1986.



It's horrendous!

Image and video hosting by TinyPic
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Quoting AussieStorm:

oh, don't go out,,, I can tell you know, it's not worth getting stuck just for the sake of a photo. I am a survivor of being struck.


You and Lee Trevino !
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Quoting MiamiHurricanes09:
Agreed, I don't see it anywhere near 10.1N as shown on the 00z ATCF best track.


I'd almost guarantee a TD at 5am with the info I'm seeing.
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2893. angiest
Oh my, it sure looks like the ECWMF is the contrarian model on this system.
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Quoting pottery:

Earlier this afternoon, I thought B'dos.
But it has kept west all day, mostly.
Looks like between me and you.
Tobago, Grenada.
But I am sure we will all get wetter.....


I will keep you updated :)
Thats what friends are for.
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Quoting ho77yw00d:



I love taking pictures myself but I am not going to go out and get struck knowing my luck (with this bad of a storm)

oh, don't go out,,, I can tell you know, it's not worth getting stuck just for the sake of a photo. I am a survivor of being struck.
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10.2N, 37.5W
Member Since: September 30, 2005 Posts: 0 Comments: 1606
2888. Patrap
Quoting eyesontheweather:
Hmmm. So Many of the folks I used to read and learn from are not here anymore.....Surprised your still here...glad you are. Hopefully the others are lurking and will intersede as needed.


Ty eyes,,..long time no see.

Im Like BP and Beaches..
Forever
Member Since: July 3, 2005 Posts: 414 Comments: 125613
2887. pottery
Post 2873.
Nice loop, Keeper. Thanks.
I had not seen that.
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Well I got jumped on before, last post for the night looking at satellite all day low clouds are moving due west mid and upper want to go wnw to nw.IMO There is one line of 20 knot shear right over llc it's what has held this back. IT will probably work itself to the surface around 12n that remains to be seen.
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2885. Relix
Quoting Levi32:


Totally agree...they appear to still be tracking the center of the broad low, instead of switching to the developing surface center which will almost certainly become Colin's core.


I said I would leave but.. well... this is addicting =P.

What change in track do you think this could create?
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Quoting extreme236:


Since the center has yet to become very well-defined, I'd say 12N could be very possible for a center estimate.
Agreed, I don't see it anywhere near 10.1N as shown on the 00z ATCF best track.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
whew... home from an outstanding B'day party with many of my strange old-time friends here in the island.

..now, here to check on the potential mischief to the East.
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Quoting earthlydragonfly:


That is what I do



I love taking pictures myself but I am not going to go out and get struck knowing my luck (with this bad of a storm)
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Blog Update!

August 1, 2010 - 10:30 PM EDT - 91L On The Verge Of Becoming A Tropical Depression
Member Since: September 2, 2009 Posts: 130 Comments: 21032
2879. Levi32
Quoting Drakoen:
I don't understand why the NHC has 91L at 10.1N when the ASCAT, Windsat, and CIMSS 850mb vort clearly differ with that philosophy.


Totally agree...they appear to still be tracking the center of the broad low, instead of switching to the developing surface center which will almost certainly become Colin's core.
Member Since: November 24, 2005 Posts: 628 Comments: 26455
Quoting nrtiwlnvragn:


Don't know what the MM5B and MM5E models are but I noticed the BAMD has done that several runs in a row, slows down the track and takes that left turn.

Strange model
.
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2877. pottery
Quoting Barbados:


Do you recon the blob to your east will drift up to me or give you another good soaking?

Earlier this afternoon, I thought B'dos.
But it has kept west all day, mostly.
Looks like between me and you.
Tobago, Grenada.
But I am sure we will all get wetter.....
Member Since: Posts: Comments:

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.