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 Stormchaser2007:
If 97L follow the BAMS track it will be sheared apart.


Yes. Although for the time being it doesn't look like it is.
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513. JLPR
Quoting Drakoen:
It looks so cute lol!


xD lol
but can be quite deadly .... this small systems tend to develop fast
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512. eye
Since people like to compare invests with past major hurricanes here...how about a IVAN path?
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Quoting Drakoen:
A track slightly south of due west, for the time being, definitely helps as shown on the XTRAP.


Agreed, and steering layers suggests that; but, sat appears to show it has moved about a degree more northwards since this early this morning - or am I not seeing this correctly?
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting Stormchaser2007:
If 97L follow the BAMS track it will be sheared apart.


I can't see it gaining that much poleward momentum. The BAMM and LGEM have the right idea. At least for now.
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It looks so cute lol!
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Quoting weatherwatcher12:

Should Jamaica watch his?


If I was there I would be watching (given the steering flow) and it now appears a rather problematic disturbance.
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If 97L follow the BAMS track it will be sheared apart.
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Quoting StormW:
Afternoon Drak and SJ.


Hello StormW
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A track slightly south of due west, for the time being, definitely helps as shown on the XTRAP.
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Watson continued the collapse in the playoff

No storybook ending :(

Stewart Cink is about to be your 2009 British Open champion, dont think anyone saw that coming

at least an American won
Quoting Stormchaser2007:


Hm really? Im just going by what I see from shear maps and the GFS shear. So im really not that sure at this point.


As I just said in my one post, the GFS is just one model. Others suggest a more favorable environment.
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I agree extreme. Numerous outlflow boundaries are setting up from the weather activity off the Florida west coast. This could get interesting. Later those boundaries could act as mechanisms for storms either from a tropical system or other disturbances.
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Yep Drak,it was nice to have a good microwave pass that came out in a timely fashion. Will be interesting to see the TRMM pass when it comes out as well. Although it will be from this same time.
Member Since: August 17, 2005 Posts: 26 Comments: 16554
Quoting Weather456:
18 UTC Ships

Brings it to 30 knots tonight



SHIPS uses the BAMM track and the GFS for its shear forecast. There are more models out there than the GFS.
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496. eye
The meat of the hurricane season will soon be here....will it be busy or a flounder?
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The SHIPS take it to near hurricane strength.
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Quoting Drakoen:



Eyewall lol? There's a lot of things to interpret from that. Could be mid level sinking air in the lower to mid level circulation.


You could be correct there. Thats why I said eyewall-like feature.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting Drakoen:
New shear forecast from the BAMM guidance keeps shear within the marginal range.


Slows down the forward speed also.
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Quoting Weather456:


or 30 mph

Should Jamaica watch his?
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting presslord:
Any reason I can't take a nap without having to worry about shuttering up and evacuating?


ROFL!

Just lurking back about 100 posts; no way to back track over 200. LOL


I still see we are watching and waiting.

now back to the pool...


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18 UTC Ships

Brings it to 30 knots tonight, shows steading sgtrengthing under marginal shear of 15-20 knots and brings it 60 knots in 5 days near 22N 83W

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Quoting extreme236:


I really dont think shear is going to be a major issue at this point in time. Just my opinion. Could be wrong.


Hm really? Im just going by what I see from shear maps and the GFS shear. So im really not that sure at this point.
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New shear forecast from the BAMM guidance keeps shear within the marginal range.
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Quoting Stormchaser2007:
IF 97L does develop and IF it does survive the shear we could have trouble later on.



I really dont think shear is going to be a major issue at this point in time. Just my opinion. Could be wrong.
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Quoting nrtiwlnvragn:
AL 97 2009071918 BEST 0 122N 525W 25 1012 DB


or 30 mph
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Quoting nrtiwlnvragn:
AL 97 2009071918 BEST 0 122N 525W 25 1012 DB


30 MPH (up from 25) Pressure 1012 MB (lowered from 1013)
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Quoting cchsweatherman:
Hey Drak,

With that latest microwave pass, it would seem that a possible eyewall-like feature has been developing and is attempting to close off. Its really starting to get better organized.

Now the only question remains will be what will wind shear be as this disturbance progresses off towards the WNW. Only time will tell.



Eyewall lol? There's a lot of things to interpret from that. Could be mid level sinking air in the lower to mid level circulation.
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Quoting Stormchaser2007:
IF 97L does develop and IF it does survive the shear we could have trouble later on.


Looks like it's targeting me
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Seems like the DAM model is in disagreement
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She went down a millibar and up to 25 knots.
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Quoting presslord:
Any reason I can't take a nap without having to worry about shuttering up and evacuating?
You mean you haven't done that yet ? Remember the Wizard of Oz...
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Hey Drak,

With that latest microwave pass, it would seem that a possible eyewall-like feature has been developing and is attempting to close off. Its really starting to get better organized.

Now the only question remains will be what will wind shear be as this disturbance progresses off towards the WNW. Only time will tell.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
very well, then...Thanks! nitey nite...
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Quoting Drakoen:
She's moving slightly south of due west.

Thank you, Drak. Every steering layer suggests that movement, really.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
97L is a micromini storm. lol

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Quoting KEEPEROFTHEGATE:
nope tagged and bagged and forwarded to NHC for there response



You should change youre name .... "Barney Fife" suites you better.
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AL 97 2009071918 BEST 0 122N 525W 25 1012 DB
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She's moving slightly south of due west.
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IF 97L does develop and IF it does survive the shear we could have trouble later on.

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97L has some nice structure with some bands extending outward
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actually the more and more I think about it, I agree with the NHC

they are basing this on the shear forecasts, even if this continued to get better organized, they are saying shear will hinder development before it gets to TD status, that isnt unreasonable. Also they feel the shear will hinder it for the next 2 days, hence why the low chance is still there

If the system continues to get better organized and things change with shear; which happens quite often, you will see them act accordingly.
466. eye
hey extreme!
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465. amd
it looks like 15 degrees latitude is becoming the dividing line between favorable shear and very unfavorable shear in the Caribbean, at least in the short term.

If 97L stays below 15 degrees, it may develop. IMO.
Member Since: August 29, 2005 Posts: 0 Comments: 1024

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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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