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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the mid level circulation is now under the heaviest convection. leadind edge of 97L about 4 hrs away from SLU
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Quoting StormW:


Rough night...weatherwise?


No LOL.. I wish. Julian had an upset stomach, just put it at that..LOL.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting stormsurge39:
It looks like its leaving shear behind?
no it's not, this is heading WNW (well at least the latitude is increasing northward) its only going to get itself in even more shear.
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What does 12z mean?
2261. SLU
I am in St. Lucia. 12z is 8:00am EST
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It looks like its leaving shear behind?
2258. KEEPEROFTHEGATE (Mod)
033

WHXX04 KWBC 200523

CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION INVEST 97L



INITIAL TIME 0Z JUL 20



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 12.1 54.2 280./17.1

6 11.2 56.6 250./25.8



STORM DISSIPATED AT 6 HRS AT THE ABOVE PSN.
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Quoting canesrule1:
Good Morning, Looking at 97L now and winds are up on the quikscat and convection is definitely up on the DMAX even though its in a unfavorable area lets wait and see this just might surprise us.

you got a point
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Quoting SLU:


lol ok. it's sunny over here for now... waiting to see what 97L has to offer.


Where are you located?
Member Since: August 2, 2006 Posts: 0 Comments: 1240
SLU what time is 12Z in EST?
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2254. SLU
Quoting alaina1085:

Sun seems to be rising as we speak, should be another pleasent day... definite lay out weather! LOL



Good Morning Storm! How are you?


lol ok. it's sunny over here for now... waiting to see what 97L has to offer.
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Quoting StormW:


I'm good! How about you and that cute little guy?


Oh he is good now, we had a rough night tho :/
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2252. SLU
Quoting victoria780:
Is this a Invest anymore?Do they drop it when they dont update the graphics?


Yeh it will be reclassified at 12Z. Don't be surprised if the winds are increased to at least 30kts.
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Good Morning, Looking at 97L now and winds are up on the quikscat and convection is definitely up on the DMAX even though its in a unfavorable area lets wait and see this just might surprise us.
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Quoting wunderkidcayman:
good morning everyone
WHAT THE HELL IS GOING ON WITH 97L!!!!!!!!!!!!!!
NOTHING! Feel Sorry For Those That Hang On Like This Is Some Kind Of Relationship; Counseling Would Be in Order For Some, I Think!
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Our 97L doesn't look that bad this morning it looks to have taken advantage of the Diurnal phase but the cloud pattern looks to be sheared one this will mostly likely have a hard time making it through the day
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Quoting weathermanwannabe:
Good Morning Folks....."Ralph" is fighting an uphill battle this morning against the sheer (good call NHC) and that ULL that is sucking the life blood out of it right now but who knows what will happen down the road after it gets into the Caribbean....In the short term however, and regardless of short-term development issues, our friends in the Lesser Antilles need to batten down so to speak....A rain soaked/windy tropical wave is nothing to laugh at and will cause some flooding and mudslides down there.......


Ralph?? ROFL...
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2245. SLU
Quoting stoormfury:
NHC has continue to keep this as a wave with little development . one thing i am sure we here in St L ucia will be in for some very terrible weather later today into tomorrow.
hope carnival revellers are tuned to this developing situation


Well development looks unlikely for today but the quikscat shows 30 - 40kt winds in the thunderstorms so it deserves a little more respect. It's one of the strongest invests of the entire season so far.
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Has anyone noticed the fact that it's gaining latitude? That's really not good for it since shear increases as you head north.

Also from looking at early visible images it aappears as though the shear has killed the mid level low. All that's left at the moment is a fairly well organized highly sheared wave. Shear runs from 20kts south side of the wave to 30kts on the north side.
Member Since: Posts: Comments:
Good Morning Folks....."Ralph" is fighting an uphill battle this morning against the sheer (good call NHC) and that ULL that is sucking the life blood out of it right now but who knows what will happen down the road after it gets into the Caribbean....In the short term however, and regardless of short-term development issues, our friends in the Lesser Antilles need to batten down so to speak....A rain soaked/windy tropical wave is nothing to laugh at and will cause some flooding and mudslides down there.......
Member Since: August 8, 2006 Posts: 0 Comments: 9402
Quoting SLU:


That's good .. how's the weather over in Gonzales this morning?

Sun seems to be rising as we speak, should be another pleasent day... definite lay out weather! LOL

Quoting StormW:
Good morning alaina.


Good Morning Storm! How are you?
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting IKE:


It's a tropical wave...
Quoting Acemmett90:

wait a second doesn't this thing have winds 25mph or higher thsi is a depression


If that was the only criteria for a tropical depression we would have one in florida most days during the summer. There is a lot more to a tropical depression than 25 mph winds.
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2237. SLU
Quoting alaina1085:


Southeast Louisiana. Gonzales to be exact. A small town between Baton Rouge and New Orleans. :)


That's good .. how's the weather over in Gonzales this morning?
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2236. IKE
Quoting Acemmett90:

wait a second doesn't this thing have winds 25mph or higher thsi is a depression


It's a tropical wave...
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the rain is starting to fall here again...very overcast outside
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IT is still an invest but in the met terms and to descibe it on the surface maps it is a trpical wave
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The sun is shining here in Barbados again :(
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2231. IKE
Quoting sporteguy03:


Another long day of shear debate ahead


Fortunately I won't be here all day to read it...lol....

System isn't going to form anytime soon. Watch out for heavy rains and gusty winds though.

50 days down.
133 to go.
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Quoting WildHorseDesertTx:
Good morning from south Texas!

You know a drought is pretty bad when you find yourself hoping that a tropical system heads your way just so you get any sort of rain at all!

We've only had 3 inches of rain since last August...driving down the roads you only see dead grass and brown trees with no greenery for miles and miles and miles when normally it is lush and green. Even the prickly pear cactus is a wilted sickly tan/yellow color.

Oh, and hello to those that remember me from last year!


3 inches of rain since LAST august?? Thats crazy... sorry to hear that.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting stoormfury:
NHC has continue to keep this as a wave with little development . one thing i am sure we here in St L ucia will be in for some very terrible weather later today into tomorrow.
hope carnival revellers are tuned to this developing situation
Is this a Invest anymore?Do they drop it when they dont update the graphics?
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Quoting SLU:


morning alaina .. where are you from?


Southeast Louisiana. Gonzales to be exact. A small town between Baton Rouge and New Orleans. :)
Member Since: August 2, 2006 Posts: 0 Comments: 1240
NHC has continue to keep this as a wave with little development . one thing i am sure we here in St L ucia will be in for some very terrible weather later today into tomorrow.
hope carnival revellers are tuned to this developing situation
Member Since: Posts: Comments:
Good morning from south Texas!

You know a drought is pretty bad when you find yourself hoping that a tropical system heads your way just so you get any sort of rain at all!

We've only had 3 inches of rain since last August...driving down the roads you only see dead grass and brown trees with no greenery for miles and miles and miles when normally it is lush and green. Even the prickly pear cactus is a wilted sickly tan/yellow color.

Oh, and hello to those that remember me from last year!
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2225. SLU
Quoting alaina1085:
Morning all!


morning alaina .. where are you from?
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2224. Mikla
Plot with Upper Shear and 850 mB Vorticity. Tear Drop marke is approx location of 97L...
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good morning everyone
WHAT THE HELL IS GOING ON WITH 97L!!!!!!!!!!!!!!
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Shear will begin to weaken today starting 12z to 18z.
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Quoting IKE:
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT MON JUL 20 2009

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

CLOUDINESS AND SHOWERS CONTINUE IN ASSOCIATION WITH A TROPICAL WAVE
LOCATED A COUPLE HUNDRED MILES EAST OF THE WINDWARD ISLANDS.
UPPER-LEVEL WINDS ARE EXPECTED TO REMAIN UNFAVORABLE FOR
DEVELOPMENT OF THIS SYSTEM FOR THE NEXT COUPLE OF DAYS. REGARDLESS
OF DEVELOPMENT...LOCALLY HEAVY RAINFALL AND GUSTY WINDS WILL 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.


Another long day of shear debate ahead
Member Since: July 7, 2005 Posts: 0 Comments: 5417
Morning all!
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2216. SLU
Quoting stormpetrol:

Wow!! We must have posted quikscat at same time basically.


lol .. yeh .. pretty good wind huh?
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2215. SLU
000
ABNT20 KNHC 201140
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT MON JUL 20 2009

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

CLOUDINESS AND SHOWERS CONTINUE IN ASSOCIATION WITH A TROPICAL WAVE
LOCATED A COUPLE HUNDRED MILES EAST OF THE WINDWARD ISLANDS.
UPPER-LEVEL WINDS ARE EXPECTED TO REMAIN UNFAVORABLE FOR
DEVELOPMENT OF THIS SYSTEM FOR THE NEXT COUPLE OF DAYS. REGARDLESS
OF DEVELOPMENT...LOCALLY HEAVY RAINFALL AND GUSTY WINDS WILL 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 BRENNAN


oh well ..
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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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