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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How far south in the east carrb on monday night will the 20-30 knt winds be. "per Dr.Masters"? Does anyone know??
Looking Good!
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97 hasn't really sped up or slowed down from what I can see, it's been consistent. I have to agree that some low level spiraling is starting to take place.
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Somebody probably already said this, but no SAL left in Caribbean near 97L.



Member Since: July 11, 2006 Posts: 14 Comments: 11322
About 5 hours to D-Max where it is.
Will certainly be interesting to see what happens overnight.
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I give it a 20% chance of TD at 11PM.
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Quoting extreme236:


Doubtful. Probably more like "Shower and thunderstorm activity associated with a tropical wave about X miles east of the Lesser Antilles has become better organized. Environmental conditions appear favorable for some additional development...and a tropical depression could form during the next day or two as it moves westward at 15-20 MPH. There is a Medium chance...30 to 50 percent...of tropical cyclone formation in the next 48 hours.


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.
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she sure looks to be getting herself together now...the 2 update could be interesting..still alot of time left till then....
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106. DDR
Hey pottery,how are you?
How's the weather? You been measuring lately?
I got about 215 mm so far.
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105. WAHA
Quoting eddye:
there no shear and people get ready south fla this will be a catgory 1 hurricane and hit south fl

Hope that doesn't happen, but i think it will probably do that
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Was "decoupling" an option in the poll?
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I think it already may be a td.
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Code red at 2 pm, tropical depression tomorrow.
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Quoting pottery:
Look, a pin hole eye !!

oh, wait a sec., its a bug on my screen. Sorry...


LOL
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Quoting pottery:
Look, a pin hole eye !!

oh, wait a sec., its a bug on my screen. Sorry...


lol
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Quoting Funkadelic:


Hey drak, what track will ex97L take if it develops? I know its way to early to tell but what general area could possibly be affected?


Looking at the steering layers, it should continue to head westward into the Caribbean then northwestward in response to a trough advecting eastward over the CONUS. Could end up somewhere in the northern Caribbean.
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there no shear and people get ready south fla this will be a catgory 1 hurricane and hit south fl
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Look, a pin hole eye !!

oh, wait a sec., its a bug on my screen. Sorry...
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Quoting Funkadelic:


Hey drak, what track will ex97L take if it develops? I know its way to early to tell but what general area could possibly be affected?


97L was reactivated. Its no longer 'ex'
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94. JRRP
Quoting extreme236:


Doubtful. Probably more like "Shower and thunderstorm activity associated with a tropical wave about X miles east of the Lesser Antilles has become better organized. Environmental conditions appear favorable for some additional development...and a tropical depression could form during the next day or two as it moves westward at 15-20 MPH. There is a Medium chance...30 to 50 percent...of tropical cyclone formation in the next 48 hours.

well...
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How far N can it go before shear tears it apart in the carrb??
12z GFS isn't showing much wind shear in the Caribbean in the next 5 days.
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Quoting stoormfury:
without model concensus very few persons incuding the NHC are willing to make a call. judging from what i have been seeing in the last visible frames, i am willing to predict the TS ana will move through the central islands tomorrow morning


In all honesty I have to agree. Unless something rather unexpected happens I don't see why this won't make TS status upon reaching the antilles. It's become far more symetrical in the last few frames, with increasing and expanding convection. Almost look like banding features on the NW side. It just needs to work on that surface low and maintain the heavy convection for an extended period
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Quoting Drakoen:


You can see... it's trying to build TSTM on the southern end and/or wrap some TSTM around the center.
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I think we'll go to Orange Alert at the Two.
cool detail on wundermap but don't see anything there as weather yet except the red "L." InvestWundermap
Member Since: July 11, 2006 Posts: 14 Comments: 11322
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Quoting Drakoen:


Looks like low level spiral bands are developing. Interesting.
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85. IKE
Quoting extreme236:


Doubtful. Probably more like "Shower and thunderstorm activity associated with a tropical wave about X miles east of the Lesser Antilles has become better organized. Environmental conditions appear favorable for some additional development...and a tropical depression could form during the next day or two. There is a Medium chance...30 to 50 percent...of tropical cyclone formation in the next 48 hours.


I'll go with yours.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Not so sure.

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Quoting BurnedAfterPosting:


looking at the visible loop I really feel it has slowed down


That can't help but aid development.
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without model concensus very few persons incuding the NHC are willing to make a call. judging from what i have been seeing in the last visible frames, i am willing to predict the TS ana will move through the central islands tomorrow morning
Member Since: August 22, 2006 Posts: 0 Comments: 2678
If only nowcoast had ability to animate...

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Quoting pottery:
Post 65. Is that you, Stormtop??


no that's not him. He is Stormno this year, and he doesn't post links or graphics.
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Quoting JRRP:
i think NHC will say:
SHOWERS AND THUNDERSTORMS HAVE INCREASED IN ASSOCIATION WITH A
WELL-DEFINED TROPICAL WAVE LOCATED ABOUT 400 MILES EAST OF THE
LEEWARD ISLANDS.DEVELOPMENT OF THIS SYSTEM...IF ANY...WILL BE SLOW TO
OCCUR AS IT MOVES WESTWARD AT 15 TO 20 MPH. . THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS


Doubtful. Probably more like "Shower and thunderstorm activity associated with a tropical wave about X miles east of the Lesser Antilles has become better organized. Environmental conditions appear favorable for some additional development...and a tropical depression could form during the next day or two as it moves westward at 15-20 MPH. There is a Medium chance...30 to 50 percent...of tropical cyclone formation in the next 48 hours.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Stormchaser2007:
Hm looks to be moving near 25mph. Thats its only problem now.


looking at the visible loop I really feel it has slowed down
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Quoting JRRP:
i think the NHC will say:
SHOWERS AND THUNDERSTORMS HAVE INCREASED IN ASSOCIATION WITH A
WELL-DEFINED TROPICAL WAVE LOCATED ABOUT 400 MILES EAST OF THE
LEEWARD ISLANDS.DEVELOPMENT OF THIS SYSTEM...IF ANY...WILL BE SLOW TO
OCCUR AS IT MOVES WESTWARD AT 15 TO 20 MPH. . THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS


Sounds about right, I think we stay in the yellow with the next TWO.
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Post 65. Is that you, Stormtop??
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Bye Aussie...
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Hm looks to be moving near 25mph. Thats its only problem now.
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72. JRRP
i think the NHC will say:
SHOWERS AND THUNDERSTORMS HAVE INCREASED IN ASSOCIATION WITH A
WELL-DEFINED TROPICAL WAVE LOCATED ABOUT 700 MILES EAST OF THE
LEEWARD ISLANDS.DEVELOPMENT OF THIS SYSTEM...IF ANY...WILL BE SLOW TO
OCCUR AS IT MOVES WESTWARD AT 15 TO 20 MPH. . THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS
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Goodnight all
Goodnight alaina1085
C'yas in the morning
And no fighting ya'll
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Yeah, that is pretty impressive consolidation of the heavy convection.
Watch the rains from this one Stormdude.
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Quoting Drakoen:


Whether that trough rips it up or not.


Ah ok, guess we will see

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Quoting BurnedAfterPosting:


close call for what?


Whether that trough rips it up or not.
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I'm hoping the shear remains high in the carib. If she blows up, the shear could knock her back down.
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Quoting Drakoen:
Looks like it's going to be a close call...


I'd say pretty even chance for either favorable or unfavorable conditions in the Caribbean when it gets there.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Link
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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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