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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WHXX01 KWBC 191217

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

ATTENTION...NATIONAL HURRICANE CENTER

1217 UTC SUN JUL 19 2009



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



ATLANTIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (AL972009) 20090719 1200 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

090719 1200 090720 0000 090720 1200 090721 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 12.4N 50.2W 13.0N 54.0W 13.9N 58.2W 15.3N 62.2W

BAMD 12.4N 50.2W 12.5N 52.8W 12.7N 55.1W 13.1N 57.6W

BAMM 12.4N 50.2W 12.8N 53.1W 13.3N 56.2W 14.0N 59.2W

LBAR 12.4N 50.2W 12.6N 53.7W 12.9N 57.5W 13.6N 61.3W

SHIP 20KTS 24KTS 29KTS 32KTS

DSHP 20KTS 24KTS 29KTS 32KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

090721 1200 090722 1200 090723 1200 090724 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 16.6N 66.7W 19.8N 74.8W 22.9N 80.3W 25.4N 82.4W

BAMD 13.4N 60.5W 14.0N 67.8W 14.5N 76.1W 14.2N 84.8W

BAMM 14.9N 62.7W 17.1N 70.5W 19.3N 78.1W 20.8N 84.1W

LBAR 14.3N 65.3W 16.1N 72.7W .0N .0W .0N .0W

SHIP 35KTS 37KTS 42KTS 53KTS

DSHP 35KTS 37KTS 42KTS 52KTS



...INITIAL CONDITIONS...

LATCUR = 12.4N LONCUR = 50.2W DIRCUR = 270DEG SPDCUR = 20KT

LATM12 = 12.3N LONM12 = 46.2W DIRM12 = 272DEG SPDM12 = 20KT

LATM24 = 12.0N LONM24 = 42.0W

WNDCUR = 20KT RMAXWD = 40NM WNDM12 = 20KT

CENPRS = 1013MB OUTPRS = 1014MB OUTRAD = 100NM SDEPTH = S

RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM



$$

NNNN


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Hunkerdown, post 197.
You are correct there. Also, the ITCZ is looking very dry again. Strange...
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Quoting beell:
This trough does not look all that bad. A shortwave trough at best-with the worst of it (shear-wise) moving to the northeast of 97L. It would be the strong upper flow following the shortwave around the SA anti-cyclone that will do a number on 97L. Steering would suggest this is where it is heading, but if it can stay to the south and move under the upper high then 2-3 days of very good conditions for devlopment.

Photobucket


Nice obs, beell. Thanks. Yes, I'm not too concerned about the trough, although if 97L gets a little more organized and gains a couple of degrees in latitude from the initial coriolis, I do think it will have some effect on steering eventually - maybe perhaps a bit further north. For now, I'm speculating that it will hold to the westerly steering pattern for the most part until it becomes better organized. Another thing, it's an upper level trough - that does little to effect what's happening at the sfc with 97L imo.
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Quoting StormFreakyisher:
Um is anyone looking at the wave east of 97L.It has a flare up in some thunderstorms now.
Do you mean to the West ? If so, THAT is from shear.
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201. potteryHi Nole, Gamma.
Some fun times ahead ? About time we had something to quarrel about !
heheheheh



lol...i hear ya...
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sngalla, gamma- no, stormno is not using all caps anymore. But I bet he will before Season™ is over.

STORMMASTERG is not Lenny.
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207. IKE
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206. beell
Quoting BurnedAfterPosting:


A few days ago most models were forecasting near perfect conditions in the Caribbean in 5-7 days and I bet it has to do with that anticyclone.


The current BAMS run does not look too out of wack (a wnw track) but this would place the storm right in the face of the westerlies and a ton of land interaction.
Member Since: September 11, 2007 Posts: 142 Comments: 16478
Quoting StormFreakyisher:
Um is anyone looking at the wave east of 97L.It has a flare up in some thunderstorms now.


East or West?

I see nothing else in the Atlantic other than 97L, if you mean the area in the Caribbean, that convection is shear induced
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Hi Snaglla, so looks like we will be keeping an eye to our SE for a few days.

Hi pottery..

hi everyone..

got to leave for a while..bbl
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Um is anyone looking at the wave east of 97L.It has a flare up in some thunderstorms now.
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Quoting BurnedAfterPosting:


not at all really, conditions were near perfect for both Emily and Felix; also future tracks take this to the NW Caribbean and not mainly due west in time

funny thing Felix was in perfect condition but when it formed they said it would only be a cat one even with the extra predicted time over the west Caribbean. (Felix was originally supposed to track N of Nicaragua.
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Hi Nole, Gamma.
Some fun times ahead ? About time we had something to quarrel about !
heheheheh
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Quoting sporteguy03:
I think the next 48 hours are what is important 5 days out conditions can change one way or another, heck they did in 24 hours.
Exactly.
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Felix also developed under a strong ridge.
Link

Weather Brainiacs: Analyze similarities and differences between conditions for Felix and 97L. Discuss amongst yourselves...
Then submit three-paged report, double-spaced (no typos!) LOL.

I think that was one of the top three fastest CAT5's to form in the history of hurricane tracking. It also formed at the end of August, not mid-July. So please, do not think we've got another Felix on our hands, folks.
I captured this image of Felix Sunday, Sept. 2, 2007.

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Quoting weatherwatcher12:

No a wave just came of last night
That was last night, I said ACROSS Africa (which means currently), not what has previously exited.
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Satellite imagery continues to show good rotation and convection organizing.
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Quoting beell:
This trough does not look all that bad. A shortwave trough at best-with the worst of it (shear-wise) moving to the northeast of 97L. It would be the strong upper flow following the shortwave around the SA anti-cyclone that will do a number on 97L. Steering would suggest this is where it is heading, but if it can stay to the south and move under the upper high then 2-3 days of very good conditions for devlopment.

Photobucket


A few days ago most models were forecasting near perfect conditions in the Caribbean in 5-7 days and I bet it has to do with that anticyclone.
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I say we ignore the models for the next 24-36 hrs
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I'll be here all night to give you guys my weather obs....
Quoting seflagamma:


Hi Aqua,
thanks for the info...

does he still post in all caps??? lol


Hey neighbor. Yes, he does.
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Quoting CybrTeddy:
pat: Funktop? Is it disco time already?


ROFL... It's always disco time :)
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189. beell
This trough does not look all that bad. A shortwave trough at best-with the worst of it (shear-wise) moving to the northeast of 97L. It would be the strong upper flow following the shortwave around the SA anti-cyclone that will do a number on 97L. Steering would suggest this is where it is heading, but if it can stay to the south and move under the upper high then 2-3 days of very good conditions for devlopment.

Photobucket
Member Since: September 11, 2007 Posts: 142 Comments: 16478
187. IKE
Less than 30%? No way...at least 30-50%.

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Quoting CUBWF:
I don't understand why dr. master said it's surrounded by dry air. Moisture is all around the wave, with just some spot of dry air to it's nw

He said it was read on and you will see that he said it is moist now.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting aquak9:


no that's not him. He is Stormno this year, and he doesn't post links or graphics.


Hi Aqua,
thanks for the info...

does he still post in all caps??? lol
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It's hard to forecast what shear will be like in the western Caribbean as the models are handling the upper level high differently. The UKMET, NOGAPS, ECMWF have favorable conditions with the high advecting from the central Caribbean into the western Caribbean. The CMC has completely unfavorable conditions. The GFS has marginal and then unfavorable condtions.
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Quoting StormFreakyisher:
Something to compare this storm too although it will definitely not be a Cat 5 in these current conditions.
Emily

Felix
Posting historical tracks are fine but they mean nothing unless the conditions/features then were the same same as they are now.
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If things are like it is now,I cant be surprised if NHC puts out a Special Tropical Weather Outlook product.What do all think of that happening?
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155. pottery 4:45 PM GMT on July 19, 2009
It is interesting, how the clouds to the s/ west and n/ east (generally) are begining to look like feeder bands.........


yeah i also was thinking that after patrap's image, after these past few seasons it seems to expect the unexpected...nothing suprises me anymore..lol
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I think the next 48 hours are what is important 5 days out conditions can change one way or another, heck they did in 24 hours.
Member Since: July 7, 2005 Posts: 0 Comments: 5270
178. CUBWF
I don't understand why dr. master said it's surrounded by dry air. Moisture is all around the wave, with just some spot of dry air to it's nw
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pat: Funktop? Is it disco time already?
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Quoting BurnedAfterPosting:


not at all really, conditions were near perfect for both Emily and Felix; also future tracks take this to the NW Caribbean and not mainly due west in time

Well then I guess I should keep an eye on this and pay attention to the Met service
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting WeatherStudent:


If it did, it would be a spec of clouds because wind shear would destroy it.
If it can get through the shear in the Caribbean and thread through the Yucatan, with shear expected to be on the decrease it will have favorable shear conditions in the GOMEX.
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Quoting pottery:
Post 65. Is that you, Stormtop??



roflmao! oh those Stormtop post from summer of 2005!
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Chicklet,Dr Masters said,"If there is anything left when it enters the western carrib,is when it when developement is possible". He was referring to the 20-30knt winds it will encounter in the eastern carrib.I also took it to mean that is when we have to worry about a land threat.
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Quoting StormFreakyisher:
Something to compare this storm too although it will definitely not be a Cat 5 in these current conditions.
Emily

Felix


not at all really, conditions were near perfect for both Emily and Felix; also future tracks take this to the NW Caribbean and not mainly due west in time
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Quoting alaina1085:


Thats cause 97L is a gangsta! LOL.


Lol....Bigtime female-wannabe lowrider....
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lol @ gangsta storm
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Quoting jasoniscoolman09:
wow did anyone see this storm yet..

I saw it last night
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Above 16N LAT. WILL GET "RIP" APART IF SHEAR CONDITIONS REMAIN AS THEY ARE AT THE MOMENT.But it seems that a ridge from north south America will lift the TUTT up. Is a wait and see situation. My humble opinion, not an expert!
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Something to compare this storm too although it will definitely not be a Cat 5 in these current conditions.
Emily

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