97L growing more organized, will bring heavy rain to the Lesser Antilles
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
Reader Comments
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Wondered that myself. Have to watch the shear line. The clouds down here have been weird lately. Still having a hard time setting up a solid sea breeze which is odd for this time of year.
AXNT20 KNHC 192334
TWDAT
TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN JUL 19 2009
TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.
BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2245 UTC.
...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 41W/42W S OF 19N MOVG W NEAR 20 KT.
THIS WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY. THIS WAVE IS JUST W OF A
DRY SAHARAN AIR LAYER. DUE TO THE PRESENCE OF THIS DRY AIR...NO
DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE.
A TROPICAL WAVE IS ALONG 52W S OF 18N MOVG W NEAR 15 KT. THIS
WAVE COINCIDES WITH A LOW TO MIDDLE LEVEL CYCLONIC CIRCULATION
NEAR THE WAVE AXIS AT 13N. SCATTERED MODERATE CONVECTION IS FROM
12N-15N BETWEEN 51W-54W.
A HIGH AMPLITUDE TROPICAL WAVE IS ALONG 71W S OF 26N MOVG W
20-25 KT. THIS WAVE COINCIDES WITH A HIGH AMPLITUDE MOISTURE
MAXIMUM OBSERVED ON TOTAL PRECIPITABLE WATER IMAGERY. AN
INVERTED-V PATTERN OF LOW CLOUDS IS ALSO EVIDENT ON VISIBLE
SATELLITE IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS FROM 16N-20N BETWEEN 69W-72W INCLUDING PORTIONS OF CUBA. THIS
WAVE MAY FRACTURE OVER THE NEXT DAY WITH THE N PORTION OF THE
WAVE FORMING A TROUGH THAT WILL CONTINUE TO THE NW...WHILE THE S
PORTION OF THE WAVE CONTINUES TO PROPAGATE WWD.
...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N15W 7N27W 10N40W 10N51W 9N62W.
SCATTERED MODERATE CONVECTION IS FROM 9N-13N BETWEEN 13W-17W. A
CLUSTER OF NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS FROM
5N-9N BETWEEN 26W-29W. SCATTERED MODERATE CONVECTION IS FROM
7N-14N BETWEEN 60W-64W.
...DISCUSSION...
THE GULF OF MEXICO...
A STATIONARY FRONT IS OVER THE NRN GULF OF MEXICO ALONG 31N81W
28N88W 29N96W. AN UPPER LEVEL TROUGH EXTENDING DOWN THE ERN
CONUS INTO THE GULF TO NEAR 26N90W SUPPORTS THE FRONT. SURFACE
CONVERGENCE AHEAD OF THE FRONT ALONG WITH UPPER LEVEL DIFFLUENCE
ARE SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM 24N-29N E OF
96W. THE REMAINDER OF THE GULF IS UNDER A BROAD SURFACE RIDGE
ANCHORED BY A 1020 MB SURFACE HIGH NEAR 26N87W BRINGING
GENERALLY FAIR WEATHER S OF 24N. A MID-LEVEL DRY SAHARAN AIR
LAYER IS ACROSS THE SRN GULF OF MEXICO SUPPORTING THE NOTED FAIR
WEATHER. LIGHT ANTICYCLONIC FLOW IS AROUND THE SURFACE RIDGE
WITH E-SE WINDS UP TO 15 KT PRESENT ACROSS THE SRN GULF...EXCEPT
FOR A SMALL PORTION OF NE WINDS UP TO 20 KT NEAR THE YUCATAN
PENINSULA COAST. EXPECT THE FRONT TO STALL TONIGHT AND BECOME
DIFFUSE TOMORROW.
THE CARIBBEAN SEA...
FAIR WEATHER IS NOTED IN THE FAR NW PORTION OF THE CARIBBEAN AS
IT IS UNDER THE INFLUENCE OF A MID-LEVEL DRY SAHARAN AIR LAYER.
HOWEVER...ATMOSPHERIC INSTABILITY IS CAUSING A FEW ISOLATED
SHOWERS TO FLARE UP OVER CUBA AND THE YUCATAN PENINSULA. AN
UPPER LEVEL RIDGE DOMINATES THE MAJORITY OF THE CARIBBEAN
CENTERED NEAR 14N75W. UPPER LEVEL DIFFLUENCE AND THE PROXIMITY
OF THE E PACIFIC ITCZ ARE SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS OVER CENTRAL AMERICA S OF 14N W OF 80W
INCLUDING PORTIONS OF NICARAGUA...COSTA RICA...AND PANAMA.
SURFACE CONVERGENCE AROUND A 1008 MB SURFACE LOW OVER COLUMBIA
NEAR 8N76W IS SUPPORTING SCATTERED SHOWER/THUNDERSTORMS S OF 10N
BETWEEN 75W-78W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL
RIDGE OVER THE CARIBBEAN AND AN UPPER LEVEL LOW IN THE ATLC NEAR
27N55W IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS OVER THE
ERN CARIBBEAN N OF 14N BETWEEN 63W-69W. THIS SHOWER ACTIVITY IS
PROBABLY BEING ENHANCED BY THE TROPICAL WAVE ALONG 71W.
SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO AFFECTING THE SRN
LESSER ANTILLES S OF 14N W OF 62W DUE TO UPPER LEVEL DIFFLUENCE
AND THE PROXIMITY OF THE ATLC ITCZ. EXPECT A SECOND TROPICAL
WAVE TO REACH THE ERN CARIBBEAN EARLY TUE.
THE ATLANTIC OCEAN...
SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS S FLORIDA ENTERING
THE ATLC AND APPROACHING THE BAHAMAS FROM 25N-29N W OF 79W. THIS
SHOWER ACTIVITY IS SUPPORTED BY A SMALL UPPER LEVEL LOW OVER THE
BAHAMAS NEAR 25N77W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER
LEVEL TROUGH OVER THE ERN CONUS AND AN UPPER LEVEL RIDGE
CENTERED AROUND 39N54W IS SUPPORTING ISOLATED
SHOWERS/THUNDERSTORMS ACROSS THE SW NORTH ATLC N OF 24N BETWEEN
68W-75W. THE REMAINDER OF THE ATLC IS DOMINATED BY A BROAD RIDGE
ANCHORED BY A 1029 MB SURFACE HIGH N OF THE DISCUSSION AREA NEAR
35N46W BRINGING GENERALLY FAIR WEATHER ACROSS THE MAJORITY OF
THE CENTRAL AND ERN ATLC. HOWEVER...A LINE OF SHOWERS ARE FROM
17N58W TO 24N50W DUE TO UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER
LEVEL HIGH NEAR 15N50W AND AN UPPER LEVEL LOW NEAR 27N55W.
$$
WALTON
I'd prefer that you were correct, but I think you're missing this one, Adrian, and being overly conservative as usual.
97L is in an area of little or no inhibiting shear in the present, or near present, for miles yet. It is better organized, imagery suggests it is trying to form an llc. Certainly, it has a good strong, mid-level circ, but convection was diminished through dmin as any system would respond usually. Now, when it has the greater opportunity to create more t'storm activity with a greater chance of lift between the differences in sfc and atmospheric temps, you want to assume that it won't increase convection. I don't understand that, because it should.
What? Thought it was depression already lol.
They are.
I see everyone is still in place arguing over 97L.
I'm on the right blog.
Now this is where your tone starts to seem condescending
Agreed.
I took a nap. No sense in hearing the same redundant info over and over again.
"llc" is low level circulation, correct?
Exactly. Just the same stuff over and over and over.
Jeez...go take a walk...mow the yard...play with your kids...
looks like we should be watching the east coast for development.
Floater 1 - JSL Color Infrared Loop
yes
WS we said shear was affecting it, doesnt meant to forget about it and look at a wave 2000 miles to its east that will take days and days to develop
is this WS..... JFW, just wondering..
YOu can go back and check but I have been a downcaster since the beginning. never thought it had a shot to survive the shear and still dont. I think I am one day off on when I thought it would get there. I thought it would have been there today but looks like tomorrow is the day we will see it go totally poof.
If anyone pretends they think they know 100% what will happen, they are pulling your leg.
This has caused the shear levels associated with the TUTT to increase substantially, especially in the region between 12 and 15 degrees north and east of the lesser antilies. That is why some shear maps have shown a 20+ knot increase in shear in this region, and why many experts, including the NHC, do not think 97L will develop.
no problem.
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SUN JUL 19 2009
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE
LOCATED ABOUT 400 MILES EAST OF THE WINDWARD ISLANDS CONTINUES TO
SHOW SIGNS OF ORGANIZATION. 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 ON
MONDAY 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
WWWW
Quoting Nolehead:
do any of the models suggest anything developing from this frontal boundary that's draped in the GOM right now?? weird front for July...very hot waters right now..things might start popping up before we know it...
Wondered that myself. Have to watch the shear line. The clouds down here have been weird lately. Still having a hard time setting up a solid sea breeze which is odd for this time of year.
i know it almost feels like late Sept not JULY!!! weird stuff..
Good point, Ike. Think I'll run some errands and come back later on when 97L is a naked swirl. I like my crow served sweet and plentiful.
Ya'll have fun "swirl" watchin'! ;)
I am with you...it is the right time of year for it and the water is ready. That front is still producing some solid thunderstorms. watch the shear line for something to spin when it stalls out.
ruff! ruff!
OMG...LOL.
ABNT20 KNHC 192350
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SUN JUL 19 2009
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE
LOCATED ABOUT 400 MILES EAST OF THE WINDWARD ISLANDS CONTINUES TO
SHOW SIGNS OF ORGANIZATION. 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 ON
MONDAY 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.
$$
FORECASTER PASCH
very interesting working, seems they have backed off on the shear unfavorable and the system has become better organized
but that shear variable is a good reason to keep it yellow
cool, thank you
ABNT20 KNHC 192350
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SUN JUL 19 2009
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE
LOCATED ABOUT 400 MILES EAST OF THE WINDWARD ISLANDS CONTINUES TO
SHOW SIGNS OF ORGANIZATION. UPPER-LEVEL WINDS ARE EXPECTED TO
BECOME LESS FAVORABLE FOR THE DEVELOPMENT OF THIS SYSTEM OVER THE
NEXT 24 TO 48 HOURS. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY
RAINFALL AND GUSTY WINDS COULD AFFECT THE WINDWARD ISLANDS ON
MONDAY AS THE WAVE MOVES WESTWARD AT 15 TO 20 MPH. THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER PASCH
Appreciate that, TN.
Catch up with y'all later. I hope it dissipates, but it is certainly interesting to watch - guess that's why most of us are here.
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