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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Link 18Z WRF SHEAR.
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That shear lifts,play the model run igave the link before.
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Quoting Ossqss:
I would offer this, Weather456 and Drakoen, we value your input very much along with many others input. I hope we can continue to enjoy the pleasure of your presence as we move forward. I cannot speak for anyone but myself, but I thank you for what you do for all of us. It is appreciated, desired, and very educational. The same respect to others who provide exceptional input -- :)


What....no love for those who provide common sense input? There's plenty of room for both.
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Quoting BahaHurican:
Evening all. I see 97L has been holding its own. Anyone with thoughts that it might survive the CAR shear?


I think it has the potential to, but it's a slim one, given its small size.

I think that it has the best chance to develop at around 75W in the next few days.
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1611. Relix
What the heck is up with 97L? =P
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Evening all. I see 97L has been holding its own. Anyone with thoughts that it might survive the CAR shear?
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Quoting STORMMASTERG:


I see 20-30 knots of shear in the southern caribbean in that model too
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1607. Ossqss
I would offer this, Weather456 and Drakoen, we value your input very much along with many others input. I hope we can continue to enjoy the pleasure of your presence as we move forward. I cannot speak for anyone but myself, but I thank you for what you do for all of us. It is appreciated, desired, and very educational. The same respect to others who provide exceptional input -- :)

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1606. SLU
Quoting Weather456:



heck, sometimes I lay a night thinking of a Caribbean NWS, establising better weather observing networks, warning systems, etc, across the region. Maybe one day, the resources will show up to start one.


Yeh man .. we'll be the 1st two onboard
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1603. CosmicEvents 12:52 AM GMT on July 20, 2009
Seems (generally) to be true that the older folk((myself included..lol) have said consistntly from the start of this on again off again invest, that it's something to keep a wary eye on.


couldn't agree anymore......
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1604. JRRP
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Seems (generally) to be true that the older folk((myself included..lol) have said consistntly from the start of this on again off again invest, that it's something to keep a wary eye on.
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1601. JRRP
Link
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Link 18z wrf shows 5 to 15kt shear still.
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Well I never agreed that it would be a TD today, as in my post last night, I said it would organize enough to regenerate to an INVEST again, and it did. Tonight?? Same darn thing! :P

Conditions are not conductive for a TD, but it may come close tonight before it hits the 20-30 knots of wind shear.
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1598. beell
Hey jeffs!
Well. there are two of us anyway...
Member Since: September 11, 2007 Posts: 141 Comments: 16200
000
WHXX01 KWBC 200026
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0026 UTC MON JUL 20 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) 20090720 0000 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090720 0000 090720 1200 090721 0000 090721 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 12.5N 53.8W 13.4N 57.5W 14.7N 61.1W 16.2N 65.1W
BAMD 12.5N 53.8W 12.9N 56.1W 13.5N 58.4W 14.0N 61.0W
BAMM 12.5N 53.8W 13.1N 56.7W 14.0N 59.6W 14.8N 62.8W
LBAR 12.5N 53.8W 13.2N 57.0W 14.3N 60.4W 15.5N 63.9W
SHIP 25KTS 28KTS 31KTS 33KTS
DSHP 25KTS 28KTS 31KTS 33KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090722 0000 090723 0000 090724 0000 090725 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 17.9N 68.7W 21.4N 75.6W 24.5N 79.5W 26.8N 80.6W
BAMD 14.6N 64.1W 15.7N 71.2W 16.3N 78.3W 15.9N 85.3W
BAMM 15.9N 66.3W 18.2N 73.6W 20.2N 79.7W 21.5N 84.3W
LBAR 16.9N 67.5W 20.2N 73.8W 22.8N 77.0W 25.6N 75.9W
SHIP 36KTS 40KTS 43KTS 48KTS
DSHP 36KTS 40KTS 43KTS 47KTS

...INITIAL CONDITIONS...
LATCUR = 12.5N LONCUR = 53.8W DIRCUR = 280DEG SPDCUR = 17KT
LATM12 = 12.3N LONM12 = 50.3W DIRM12 = 269DEG SPDM12 = 20KT
LATM24 = 12.3N LONM24 = 46.2W
WNDCUR = 25KT RMAXWD = 40NM WNDM12 = 20KT
CENPRS = 1011MB OUTPRS = 1013MB OUTRAD = 120NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

$$
NNNN

Tropical Cyclone Guidance Message from here
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Quoting stormdude77:


Link

thanks

Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:

can you link me to that site


Link
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1594. JRRP
12 GMT 07/19/09 12.4N 50.2W 20 1013 Invest
18 GMT 07/19/09 12.2N 52.5W 25 1012 Invest
00 GMT 07/20/09 12.5N 53.8W 25 1011 Invest
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97L seems to have slowed down a bit...that could be a positive factor for the system....
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One thing I find interesting:
"
UPPER-LEVEL WINDS ARE EXPECTED TO
BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS SYSTEM OVER THE
NEXT 24 TO 48 HOURS."

Changed from:

"UPPER-LEVEL WINDS ARE EXPECTED TO
BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS SYSTEM LATER TONIGHT."

Those mean the EXACT SAME THING. When someone says "over the next 24 to 48 hours", that means that something will be changing within 24 hours. Aka... possibly tonight.

edit: I see Beell beat me to it.
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Quoting stormdude77:
19/2345 UTC 12.4N 53.5W T1.0/1.0 97L -- Atlantic

can you link me to that site
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting BurnedAfterPosting:
The flip-flopping is very funny on this blog

seems most cant stay consistent

although I think Drak is playing Devils' advocate more than anything lol


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19/2345 UTC 12.4N 53.5W T1.0/1.0 97L -- Atlantic
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1588. WxLogic
Quoting Drakoen:
Should start writing up that requiem...


I think I got one somewhere around here for when Fay passed away... where is it!!!
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1587. Ossqss
Are we learning that Mother Nature does not play by the rules sometimes ? The only consistent thing is the inconsistency of what we have been seeing :)
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WS I guess you want this system to develop huh?

or else you wouldnt be so disappointed
The flip-flopping is very funny on this blog

seems most cant stay consistent

although I think Drak is playing Devils' advocate more than anything lol
1583. Drakoen
Quoting weatherwatcher12:

Where's Avila?


Not on duty at that time. Rhome is the one in the red.
Member Since: October 28, 2006 Posts: 57 Comments: 29883
1581. JRRP
Link
Link
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Quoting Drakoen:
Pasch looking at RECON data for Felix. He's the one in the chair:

Where's Avila?
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1579. Drakoen
Should start writing up that requiem...
Member Since: October 28, 2006 Posts: 57 Comments: 29883
1577. HadesGodWyvern (Mod)
Central Pacific Hurricane Center: Honolulu, Hawaii

Tropical Cyclone Outlook (10:00 AM HST 19JUL)
==============================================
A surface trough more than 500 miles south-southwest of the Big Island of Hawaii has been moving west near 15 mph. Showers and thunderstorms associated with the system have weakened over the past six hours.

Tropical cyclone development in the area is unlikely over the next 48 hours.
Member Since: Posts: Comments:
Quoting SLU:



Not having one of their best years I reckon. By now the total count should be 2 tropical storms so far for the season. Maybe you should apply for a job there or we should establish our own Eastern Caribbean Hurricane Center. What you think?



heck, sometimes I lay a night thinking of a Caribbean NWS, establising better weather observing networks, warning systems, etc, across the region. Maybe one day, the resources will show up to start one.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1575. Drakoen
SHIPS 00z doesn't make shear favorable.
Member Since: October 28, 2006 Posts: 57 Comments: 29883
1574. 0741
ty for your answer storm w
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Quoting bjdsrq:
Looked like a hurricane that hit Siesta Beach today around 3:45pm. I saw the bow echo and knew the incoming squalls were going to have some kicking winds so I grab my gear and headed to the beach. Here's the video:
Siesta Beach Wind Storm - July 19, 2009



Great vid. You would think if you had time to get there, sunbathers would had had time to leave before the blow. That was one NASTY storm.
p.s. Thanks for the bikini shots :)
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1572. Drakoen
Pasch looking at RECON data for Felix. He's the one in the chair:
Member Since: October 28, 2006 Posts: 57 Comments: 29883
Quoting nrtiwlnvragn:
AL 97 2009072000 BEST 0 125N 538W 25 1011 DB

Can you link me to the site please
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1570. SLU
Quoting Weather456:
lol I can't remember the blog being this funny, and the NHC being this inconsistent.97L is one for the books. Every time the GFS changes we get a change in the TWO:

UPPER-LEVEL WINDS ARE EXPECTED TO
BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS SYSTEM OVER THE
NEXT 24 TO 48 HOURS.


previously it was:

UPPER-LEVEL WINDS ARE EXPECTED TO
BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS SYSTEM LATER TONIGHT.




Not having one of their best years I reckon. By now the total count should be 2 tropical storms so far for the season. Maybe you should apply for a job there or we should establish our own Eastern Caribbean Hurricane Center. What you think?
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1569. WxLogic
Quoting nrtiwlnvragn:
They changed the 18Z data from 1012 to 1011, so with the 00Z at 1011, no pressure drop, but the one at 18Z is now -2 LOL

They also changed the system from shallow to medium.


I though it was going to stay shallow enough to avoid the full brunt of the shear.
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Quoting futuremet:
lol It would be discreet if NHC ever say "WE JUST DON'T KNOW!"

Basically, they are. It's not much more than a coin flip as to what will happen 48+ hours down the road.
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They changed the 18Z data from 1012 to 1011, so with the 00Z at 1011, no pressure drop, but the one at 18Z is now -2 LOL

They also changed the system from shallow to medium.
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First post here. Been a fan for over a year. Not skilled enough to make any predictions, but love reading and learning. Thanks guys!
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lol It would be discreet if NHC ever say "WE JUST DON'T 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.