97L growing more organized, will bring heavy rain to the Lesser Antilles

By: Dr. Jeff Masters , 3:55 PM GMT on July 19, 2009

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The tropical wave near 12N 52W, about 600 miles east of the Lesser Antilles Islands (97 L), has grown more organized this morning as it tracks west at about 20 mph. This wave is surrounded by an area of very dry air from the Sahara Desert, but 97L has been able to steadily moisten a large region of the atmosphere over the past day, insulating itself from the dry air. This moistening process has been aided by sea surface temperatures (SSTs) that have steadily increased from 26.5°C to 27.5°C, plus the presence of only 10 knots of wind shear. The system now has a small area of intense thunderstorms near its center, with some rotation of the cloud pattern evident at mid-levels of the atmosphere. An upper-level outflow channel has opened to the north, and there is evidence that surface spiral bands are beginning to form. This morning's QuikSCAT pass missed 97L, so we don't know what is happening at the surface.

Wind shear is a modest 10 knots over the disturbance, and is forecast to remain in the moderate 10 - 15 knot range through Monday morning. This should allow further development to occur today, and 97L could be approaching tropical depression strength on Monday as it moves through the central Lesser Antilles Islands. Monday night, shear is expected to rise to 20 - 30 knots, thanks to the presence of a trough of low pressure at upper levels of the atmosphere over the eastern Caribbean. Since 97L is a relatively small system, it is very vulnerable to wind shear. This shear may be able to drive some of the dry air west of 97L deep into its interior, significantly disrupting the disturbance. Shear will remain high along 97L's path through Thursday, when the storm should be in the western Caribbean near Cuba. If there is anything left of 97L by then, some development is possible. The National Hurricane Center gave 97L a low (less than 30% chance) of developing into a tropical depression in the next 48 hours in their 8am Tropical Weather Outlook. However, I'd say the odds are now in the medium range (30 - 50%).

None of the computer models are forecasting tropical storm development over the next seven days.


Figure 1. Current satellite image of African wave 97L.

I'll have an update Monday morning. As 97L approaches the islands, you may want to follow local observations there using our wundermap for 97L.

Jeff Masters

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Quoting weatherwatcher12:
Hmmm... The TUTT has move more north than previously.


actually shear has increased a bit in the southern caribbean, it will be very close
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Quoting weathermanwannabe:


It is certainly taking advantage of the immediate low sheer and threading the needle...."lowriding" below the sheer to the North and SA to the South.


Thats cause 97L is a gangsta! LOL.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting Funkadelic:
Now heres the question.. Is 97L making its OWN convection, or is it being enhanced by shear/ the TUTT


Also if it was shear induced the convection would not be consildating and becoming circular as you see it would be blowing in a direction like what happen to wave in front of 97L.
Member Since: July 7, 2005 Posts: 0 Comments: 5351
Quoting Patrap:
Shear killer.
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Quoting eddye:
there no shear and people get ready south fla this will be a catgory 1 hurricane and hit south fl


Based on what?
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There's a lotta energy out there, Patrap.
Lucky it's going in different directions!
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Quoting Drakoen:
Right now I don't see shear being favorable in the western Caribbean.


Its not gonna be 100% by any means, but if she takes the southern route like it looks she is, she should survive the killing shear to its north. Shes small and I think it will survive with some shear but not enough to destroy it
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Hmmm... The TUTT has move more north than previously.
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Quoting Chicklit:
Everyone says shear is forecast to lessen, but still, it will be amazing to me if 97L manages to negotiate the shear just to its north. So far it has managed to stay out of that fray by laying low...amazingly enough already!


shear map


It is certainly taking advantage of the immediate low sheer and threading the needle...."lowriding" below the sheer to the North and SA to the South.
Member Since: August 8, 2006 Posts: 0 Comments: 9231
It is interesting, how the clouds to the s/ west and n/ east (generally) are begining to look like feeder bands.........
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Quoting Funkadelic:
Now heres the question.. Is 97L making its OWN convection, or is it being enhanced by shear/ the TUTT
Not TUTT enhanced either, its not near 97 plus appears to be on its way out.
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Quoting BurnedAfterPosting:
poll will be closing at 1pm, so if anyone hasnt voted yet, do so before then


I'm tired of being wrong so will not vote this time. (HNI) (Have No Idea:)
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I'm hoping we get a GFDL and HWRF run. Regional models have an easier time handling these smaller systems. The GFS can't even pick up on the 850mb vort max.
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136. Patrap

very nice image...still alot of time left till the update time...place your bets place your bets...
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Quoting weatherwatcher12:

True and there are other places other than south Florida


Careful deep layer steering brings this up northwesterly eventually.Maybe some rain if theres anything left.
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Quoting Vero1:

AGXX40 KNHC 190819
MIMATS

MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE MIAMI FL
418 AM EDT SUN JUL 19 2009

...I AM NOT CONFIDENT WITH THE GFS SOLUTION
OF THIS WAVE AS IT SEEM TO MOVE IT TOO SLOWLY AND LEAVES SOME
TROFFING BEHIND ACROSS THE THE NE CARIBBEAN TODAY...WHILE
CURRENT STLT IMAGERY CLEARLY SHOWS A LOW TO MID LEVEL VORT
PASSING S OF PUERTO RICO ATTM. I THUS PREFER THE ECMWF AND UKMET
SOLUTIONS OF A FASTER MOVING WAVE...WITH MOST OF THE ENERGY AND
ACTIVE WEATHER CROSSING THE CARIBBEAN N OF 16N AND ACROSS THE
GREATER ANTILLES AND ADJACENT ATLC. A SECOND TROPICAL WAVE
CURRENTLY OVER THE CENTRAL ATLC WILL PUSH INTO THE EASTERN
CARIBBEAN BY EARLY MONDAY...REACHING ROUGHLY 68W BY EARLY
TUE...AND JAMAICA BY WED.

....FORECASTER STRIPLING




That discussion is mostly about the first wave that is already in the Caribbean, that 2nd wave it touches on briefly is 97L
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124 -- Convection is convection. In the past I've seen NHC report that storm such and such formed after an easterly wave "interacted" with a trough in the westerlies. I think that means the wave entered an area with diffluent flow aloft which intensified the convection, hence the disturbance strengthened.

I think the diffluence in their reports diminishes the significance of convection only when there is no low level convergence or vorticity to go with it.
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Thanks Dr masters.

Night Aussie.

Im still going with code orange for tonight.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Right now I don't see shear being favorable in the western Caribbean.
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Everyone says shear is forecast to lessen, but still, it will be amazing to me if 97L manages to negotiate the shear just to its north. So far it has managed to stay out of that fray by laying low...amazingly enough already!


shear map
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Quoting hunkerdown:
Has anybody noticed the lack of activity across Africa ?

No a wave just came of last night
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142. Vero1

AGXX40 KNHC 190819
MIMATS

MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE MIAMI FL
418 AM EDT SUN JUL 19 2009

...I AM NOT CONFIDENT WITH THE GFS SOLUTION
OF THIS WAVE AS IT SEEM TO MOVE IT TOO SLOWLY AND LEAVES SOME
TROFFING BEHIND ACROSS THE THE NE CARIBBEAN TODAY...WHILE
CURRENT STLT IMAGERY CLEARLY SHOWS A LOW TO MID LEVEL VORT
PASSING S OF PUERTO RICO ATTM. I THUS PREFER THE ECMWF AND UKMET
SOLUTIONS OF A FASTER MOVING WAVE...WITH MOST OF THE ENERGY AND
ACTIVE WEATHER CROSSING THE CARIBBEAN N OF 16N AND ACROSS THE
GREATER ANTILLES AND ADJACENT ATLC. A SECOND TROPICAL WAVE
CURRENTLY OVER THE CENTRAL ATLC WILL PUSH INTO THE EASTERN
CARIBBEAN BY EARLY MONDAY...REACHING ROUGHLY 68W BY EARLY
TUE...AND JAMAICA BY WED.

....FORECASTER STRIPLING


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141. Relix
Well at lest it will miss PR =P. Darn what a comeback!!
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Wait somebody mentioned it will be in the northern Carribean near Cuba because of a trough moving eastward.So does that mean it will recurvate to the north or northeast like towards Florida?
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Quoting Chicklit:
Somebody probably already said this, but no SAL left in Caribbean near 97L.



Has anybody noticed the lack of activity across Africa ?
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She looks to take the southern route into the southern tier of the islands, shear to the north of it might miss her, and she will survive if she takes the southern track and stays low away from the northern tier islands.
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Funktop Image




Floater 1 - Funktop Color Infrared Loop

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Quoting btwntx08:

don't get ahead of ur self it may not to fl imo

True and there are other places other than south Florida
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I vote B
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Drakoen what % chance do you give 97L of coming out of any unfavorable shear in the eastern carrib?
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Quoting Drakoen:
If the system continues @ 25mph it will reach the islands by this time tomorrow. Facing marginally favorable shear conditions according to the GFS 12z. Shear looks a little more favorable in the eastern Caribbean than the previous runs especially @ 36hr.Link

I have this feeling that it will slow its forward speed soon
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Quoting Funkadelic:
Now heres the question.. Is 97L making its OWN convection, or is it being enhanced by shear/ the TUTT


Its not shear induced.
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Quoting Funkadelic:
Now heres the question.. Is 97L making its OWN convection, or is it being enhanced by shear/ the TUTT


based on the cloud pattern, it is creating its own
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Quoting BurnedAfterPosting:
poll will be closing at 1pm, so if anyone hasnt voted yet, do so before then


C or Orange
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127. JRRP
Quoting SavannahStorm:


That's what the NHC should say, but I don't think they will. The NHC's trends to the conservative side when forecasting development. Especially given the fact that none of the major models develop the system, the NHC will probably play it safe with the next TWO.

i agree
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Floater 1 - Visible Loop
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poll will be closing at 1pm, so if anyone hasnt voted yet, do so before then

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It's got everything going for it right now except for the prospective sheer values out ahead of it.......She could blow out before then so it is a wait and see; but, based upon current observation, the islands may to to issue a tropical storm watch later this evening if this very impressive daytime organization continues...
Member Since: August 8, 2006 Posts: 0 Comments: 9231
Quoting SavannahStorm:


That's what the NHC should say, but I don't think they will. The NHC's trends to the conservative side when forecasting development. Especially given the fact that none of the major models develop the system, the NHC will probably play it safe with the next TWO.



Thats the kicker, but if they can get some good factual observations from a ship, buoy, or reporting station then that could sway them more.
Member Since: July 7, 2005 Posts: 0 Comments: 5351
Quoting rxse7en:
Was "decoupling" an option in the poll?


don't think so, RX7n. Mid level has been strong.

(ducks)
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hello everyone,i think the NHC will raise the alert to orange at the next TWO and they will mention they will be sending an aircraft to investigate the area if necessary,because the system is almost at 55
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post 111
EDIT, should have said D-Min.
Sorry..
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D-Min is in 5 hours, not D-Max

D-Max is just before sunrise
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If the system continues @ 25mph it will reach the islands by this time tomorrow. Facing marginally favorable shear conditions according to the GFS 12z. Shear looks a little more favorable in the eastern Caribbean than the previous runs especially @ 36hr.Link
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Okay it seems to still be moving west so it will start effecting the southern Antilles and part of the mid Antilles,then northern Venezuela,Trinidad and Tabago, and Aruba.The slower it moves the better chance the shear will lessen in time for development?or break up?
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How far south in the east carrb on monday night will the 20-30 knt winds be. "per Dr.Masters"? Does anyone know??
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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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