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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Pressure (MSLP): 1011 mb (29.85 inHg | 1011 hPa)
Sustained wind speed (1 min. avg.): 25 knots (29 mph | 13 m/s)
Member Since: May 16, 2009 Posts: 1 Comments: 1231
2113. Relix
97L is like the brave little toaster!! Haha, holding out against shear. Is it me or is there more of a noticeable WNW component right now, or is it the mess of convection messing with my eyes?
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Quoting moonlightcowboy:
It can still make it, TS - maybe not tomorrow, but maybe past the islands if it can keep some circulation intact...it's doing that so far. With some low level convergence it may be able to keep creating some good lift through dmax to maintain its spin and convection, despite the shear blowing tops off. There is no shear with 97L at the mid-levels. Additionally, the anti-cyclone is growing off the northern SA coast into the Caribbean.


agree
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Quoting CybrTeddy:


Wow Tampa, serious whats your problem this year? Calling wishcasters, insulting people, ect. You weren't anything like that last year.


Cybr know you for a long time......if i came across that to everyone i apologize...it was only intended to just a hand full..
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Convection is converging and exploding. It's defying the shear, but for how long.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
It can still make it, TS - maybe not tomorrow, but maybe past the islands if it can keep some circulation intact...it's doing that so far. With some low level convergence it may be able to keep creating some good lift through dmax to maintain its spin and convection, despite the shear blowing tops off. There is no shear with 97L at the mid-levels. Additionally, the anti-cyclone is growing off the northern SA coast into the Caribbean.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
The divergence is also increasing
Member Since: May 16, 2009 Posts: 1 Comments: 1231
SOI still positive

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Quoting moonlightcowboy:
97L is finally showing some lower level convergence as well.

very true
Member Since: May 16, 2009 Posts: 1 Comments: 1231
I'm sorry to rain on some people's parade. But 97L is about to head into 40 Knots of Vertical Wind Shear. You can already see the shear's effect on satellite. Also, to the people denying Tampaspin you shouldn't be, He has been right all along with 97L. So quit saying he is wrong and wishcasting because you are only putting whatever you think your reputation is here in jeopardy.

Some of y'all need to relax and look at a WV Loop and have fun on here and learn. That's what needs to happen here. But I can't force some of you to do it.

Wxman504
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Quoting TampaSpin:
Just looked at Data.....97L is vertually dead....it will be poof in 12hrs.....Shear will be ripping it apart!


You said the same thing last night.
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Quoting btwntx08:

but now i agree with u on the near 30 kts shear on 97L and it is still to watch after it gets though the shear so its just wait and see game for a couple of days


Honestly the shear was 15kts the other nite.....out of the NW.....if you would have zoomed in you could see the cloud tops blowing off.......5kts of shear does not cause that.....Yes it still bears some watching but, not much....LOOK East and watch the GOM and off the Atlantic seaboard the next few days.
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Quoting TampaSpin:


Many
probably did the same to you!


Wow Tampa, serious whats your problem this year? Calling wishcasters, insulting people, ect. You weren't anything like that last year.
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97L is finally showing some lower level convergence as well.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting TampaSpin:
Just looked at Data.....97L is vertually dead....it will be poof in 12hrs.....Shear will be ripping it apart!

Look at the vorticity. Increasing every 3 hours. The pressure has dropped 3 millibars in the past 24 hours
Member Since: May 16, 2009 Posts: 1 Comments: 1231
this soon to be storm doesnt care about shear.
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Just looked at Data.....97L is vertually dead....it will be poof in 12hrs.....Shear will be ripping it apart!
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Convection looks like it's trying to merge
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Definitely ragged, but definitely still some mid-level rotation and convective bursts. 97L is trying to hang despite the shear - heckuva fighter.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting btwntx08:
btw that wave at 5n 30w is still in the itcz it needs to break away from that then its something to watch but not right now


And yes i think i know that....hahaha
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Quoting btwntx08:

what the i was not wishcasting and yes i saw the quotes....and i barely came on and didn't it till now! lol


Ok....whatever along with your buddies.....its all good!
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Quoting btwntx08:
don't quote ben blogger just ingore him i did a long way back imo


Many probably did the same to you!
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Quoting Funkadelic:


It's still got great shape considering the shear... D-max is approaching and convection is building once again. Just imagine if this thing had no shear to deal with:. We would have a problem


I strongly agree with you....if the Shear would not have been present 2 days ago along with the dry conditions and cooler waters...we could have had Ana already present.
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Quoting btwntx08:

yeah a couuple days late lol


Your so wrong......go back and look at my quotes...i said it was under 10-15kts of shear..even last nite and it would increase....today and tonite....ROFLMAO.....Wishcaster!
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Quoting Funkadelic:


It's still got great shape considering the shear... D-max is approaching and convection is building once again. Just imagine if this thing had no shear to deal with:. We would have a problem


agree
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Shear is actually closer to 30-35kts imo....maybe even higher...
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Quoting weatherwatcher12:
I have to say that the wave at the bottom right is looking good


Just some itcz flare ups.
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I would not write if off either.....it still has a nice circulation intake but, in 6-12hrs the naked spin will wind down also....
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Quoting TampaSpin:


There was believers and wishcasters.........LOL


lol
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Good night y'all. We'll see if it survives the night.
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I have to say that the wave at the bottom right is looking good
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:

Don't write it off. Remember if the circulation survives the axis will move west and meet up with the anti cyclone


I ain't writing it off. still has a slim chance imo
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Quoting BenBIogger:


Both of us knew it was going to hit the brick wall of shear.


There was believers and wishcasters.........LOL
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And theres my answer. Lol.
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Quoting TampaSpin:
Good Morning everyone......Looks like 97L is getting hit with the higher shear i thought it would....


Both of us knew it was going to hit the brick wall of shear.
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Wow, 97L is ragged.
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Quoting weatherwatcher12:

Unlikely. The 850mb vorticity continues to increase. The convection may be gone but the circulation is still there.


Yeah. Looks pretty good on the RGB. And it kinda looks like its starting to go a little more northerly. or that could be because of the convection flaring up.
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000
ABNT20 KNHC 200546
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT MON JUL 20 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

CLOUDINESS AND SHOWERS ASSOCIATED WITH A TROPICAL WAVE LOCATED A
COUPLE HUNDRED MILES EAST OF THE WINDWARD ISLANDS HAVE BECOME LESS
ORGANIZED OVER THE PAST SEVERAL HOURS. UPPER-LEVEL WINDS ARE
EXPECTED TO BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS
SYSTEM OVER THE NEXT 24 TO 48 HOURS. REGARDLESS OF DEVELOPMENT...
LOCALLY HEAVY RAINFALL AND GUSTY WINDS COULD AFFECT THE WINDWARD
ISLANDS DURING THE NEXT DAY OR SO AS THE WAVE 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.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH

Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting BenBIogger:
97L is currently under 25kts of shear.

Don't write it off. Remember if the circulation survives the axis will move west and meet up with the anti cyclone
Member Since: May 16, 2009 Posts: 1 Comments: 1231
The blob at 5N 30W is the one to watch...as the Azore and Beremuda High strengthens and Shear subsides this week.....Ana will be coming from this blob!
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97L is currently under 25kts of shear.
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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.