Lesser Antilles Disturbance 97L a Threat to Develop

By: Dr. Jeff Masters , 2:46 PM GMT on September 01, 2013

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A tropical wave over the Lesser Antilles Islands (Invest 97L) is moving westward at 15 mph, and is bringing heavy rains and gusty winds to the islands. Top sustained winds in the islands as of 10 am AST Sunday were 26 mph at Monserrat. Heavy thunderstorm activity has sharply increased since Saturday, as seen on satellite loops. A large circulation is evident, with some westerly winds blowing to the south of the disturbance. However, the thunderstorms are poorly organized, and there is no sign of a well-organized surface circulation. Martinique radar shows some rotation to the echoes, though well-organized spiral bands are not evident, and do not appear to be forming. Wind shear has dropped to a moderate 10 - 20 knots over the system. An area of dry air from the Saharan Air Layer (SAL) surrounds 97L and is interfering with development.


Figure 1. Latest satellite image of Invest 97L.

Forecast for 97L
Wind shear is expected to be in the low to moderate range for the next five days, and ocean temperatures will be warm, 28 - 29°C. The disturbance is steadily moistening the atmosphere and is moving into a moister environment, so dry air will be less of an impediment to development as the week progresses. The main factor keeping the disturbance from developing over the next two days would appear to be the fact that 97L is quite large, and is stretched out from east to west over a wide expanse. Large, elongated systems like 97L usually take several days to consolidate and spin up. Another factor that will likely retard development is the presence of strong surface trade winds over the Eastern Caribbean ahead of 97L, south of the Dominican Republic. These strong trade winds are a common feature of the Eastern Caribbean, and make the region something of a hurricane graveyard. As the surface wind flow to the west of 97L accelerates into this wind max, air will be sucked from aloft downward towards the surface, creating sinking air, interfering with the formation of thunderstorm updrafts. The best chance for development of 97L would appear to be on Wednesday or Thursday, when the disturbance reaches the Central Caribbean. The wave will likely spread heavy rains to Puerto Rico, the Virgin Islands, and the Dominican Republic by Tuesday, and to Haiti by Wednesday. These rains will be capable of causing life-threatening flash flooding and mudslides in mountainous regions in Puerto Rico and Hispaniola. Of our three reliable models for predicting genesis, the UKMET, GFS, and European models, only the UKMET model develops the disturbance, predicting it will become a tropical depression south of Haiti on Wednesday, and near Jamaica on Thursday. In their 8 am EDT Sunday Tropical Weather Outlook, NHC boosted the 5-day odds of formation of 97L to 30%, and the 2-day odds to 20%.


Video 1. You can see why landslides triggered by heavy rains from a tropical cyclone are among the most dangerous hazards of these storms, thanks to a dashboard cam that caught this extraordinary rock slide in Northeast Taiwan on August 31, 2013, after heavy rains from a cold front drenched the island with up to 200 mm (7.87") of rain in 24 hours. The rains fell upon soils already saturated by Thursday's torrential rains from Tropical Storm Kong-Rey, which dumped up to 482 mm (19") of rain on Taiwan, killing three people. The driver of the car caught in the rock slide survived with minor injuries. Thanks go to wunderground member Robert Speta for bringing this video to my attention. A separate video showing the damage to the car and the course of the rock slide is here.

Jeff Masters

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Quoting 1434. Tropicsweatherpr:


Who is more conservative,Avila or Pasch?
Pasch is. When he and Bevin are on, a 50 mph TS could be construed as a DB or LO....
Member Since: October 25, 2005 Posts: 19 Comments: 21943
Stewart stated in the 2pm TWO that a westward track was likely over the next few days; NHC TAFB shows the storm southeast of Jamaica in 72 hours. Pasch comes in and says it's likely to track near or over Hispaniola in a few days. Not sure why the discrepancy, but I doubt Pasch ends up right.
Member Since: July 6, 2010 Posts: 113 Comments: 31919
Quoting 1440. sunlinepr:
Next wave looks like it could merge with 97L, if it keeps stationary....

Is that means more convection to help intensifies 97L?
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Quoting 1427. SLU:
...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED.

FORECASTER PASCH

That's not what Stewart said at 2pm. The NHC forecasters aren't on the same page.
I think the elongation has gotten worse over the last 6. When Stewart wrote, it really looked like it was tightening up and kicking out the former dominant low. Now it looks like they're working in tandem, which means the circulation is dragged into the E Car before it gets itself together....
Member Since: October 25, 2005 Posts: 19 Comments: 21943
Anyone knows what sauce is best with crow? I need some! :))
Member Since: April 29, 2007 Posts: 0 Comments: 7862
Quoting 1446. CybrTeddy:

I imagine they came in during the shift change and thought "... what are you doing Stewart?"
Doubt it. Stacy will throw some punches, no hesitation. ;)



Pictured from left to right: Jack Beven, John Cangialosi, Eric Blake, Todd Kimberlain, Richard Pasch, Robbie Berg, Lixion Avila, James Franklin, Michael Brennan, Daniel Brown and Stacy Stewart.
Member Since: September 2, 2009 Posts: 130 Comments: 21172
Quoting 1285. DonnieBwkGA:
How much rain in say 48 or 72 hours would it take to get Lake Okeechobee above 18 feet?



According to Doc's previous blog, The Battle to Draw Down Lake Okeechobee, torrential rains of 7 inches from a tropical storm or hurricane are capable of raising the lake level by over three feet in a few weeks. The current lake level is 15.55'. Danger levels for dike failure begin with levels over 16' and get incrementally more dangerous for a dike breach as levels approach 18.5' with likely failure at one or more locations more imminent at 21'. A significant storm surge could be catastrophic.



Click on the above image for level plots.


Florida Rainfall Total August 2012


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Quoting 1425. MiamiHurricanes09:
Not that I've ever seen lol.
That young guy was learning well....

lol
Member Since: October 25, 2005 Posts: 19 Comments: 21943
1447. will40
Quoting 1444. MiamiHurricanes09:
Interested to see if the 00z plots shift that way. Nothing in the synoptic pattern has changed since 12z.


may have been some of the info from the aircraft mission today at least i think they did some dropzodes
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Quoting 1427. SLU:
...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED.

FORECASTER PASCH

That's not what Stewart said at 2pm. The NHC forecasters aren't on the same page.
I imagine they came in during the shift change and thought "... what are you doing Stewart?"
Member Since: July 8, 2005 Posts: 259 Comments: 23927
Quoting 1443. Funication:



Not much dry air. It has a bigger chance than those waves out there in the east Atlantic.
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Quoting 1438. nrtiwlnvragn:


Could be, but the 18Z GFS took a weak system that way, and latest TWO says that way, so.......
Interested to see if the 00z plots shift that way. Nothing in the synoptic pattern has changed since 12z.
Member Since: September 2, 2009 Posts: 130 Comments: 21172

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Quoting 1434. Tropicsweatherpr:


Who is more conservative,Avila or Pasch?
They're all conservative lol, except for Stewart, and occasionally Blake.
Member Since: September 2, 2009 Posts: 130 Comments: 21172
Tough to believe in hurricane formation this year since the hurricane total is zilch.
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Next wave looks like it could merge with 97L, if it keeps stationary....

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Quoting 1385. Tazmanian:



you are vary late
Who honestly care if they are late or not?
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Quoting 1433. MiamiHurricanes09:
Not buying it...at all. Virtually impossible that 97L becomes a hurricane by the time it reaches Puerto Rico's longitude. That type of intensity would be the only reason it moves that poleward.

Even though I hate when people say this, until a surface circulation consolidates, model runs are a bit of a shot in the dark...although I am lenient towards a Jamaica/Cuba event.


Could be, but the 18Z GFS took a weak system that way, and latest TWO says that way, so.......
Member Since: September 23, 2005 Posts: 14 Comments: 11122
Quoting 1433. MiamiHurricanes09:
Not buying it...at all. Virtually impossible that 97L becomes a hurricane by the time it reaches Puerto Rico's longitude. That type of intensity would be the only reason it moves that poleward.

Even though I hate when people say this, until a surface circulation consolidates, model runs are a bit of a shot in the dark...although I am lenient towards a Jamaica/Cuba event.


And possibly a restregnthening in the gulf, if it doesn't hit the Yucatan. .
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1435. JRRP
WHILE IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 10 TO 15 MPH OVER
THE CARIBBEAN SEA...AND NEAR OR OVER HISPANIOLA.
Member Since: August 16, 2007 Posts: 0 Comments: 5748
Quoting 1427. SLU:
...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED.

FORECASTER PASCH

That's not what Stewart said at 2pm. The NHC forecasters aren't on the same page.


Who is more conservative,Avila or Pasch?
Member Since: April 29, 2009 Posts: 75 Comments: 14226
Quoting 1412. nrtiwlnvragn:
Big shift from 12Z





Not buying it...at all. Virtually impossible that 97L becomes a hurricane by the time it reaches Puerto Rico's longitude. That type of intensity would be the only reason it moves that poleward.

Even though I hate when people say this, until a surface circulation consolidates, model runs are a bit of a shot in the dark...although I am lenient towards a Jamaica/Cuba event.
Member Since: September 2, 2009 Posts: 130 Comments: 21172
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SUN SEP 1 2013

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

1. AN AREA OF LOW PRESSURE IS LOCATED NEAR THE LESSER ANTILLES.
SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THIS SYSTEM HAVE
DECREASED THIS EVENING...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED. ALTHOUGH UPPER-LEVEL WINDS APPEAR
TO BE CONDUCIVE...THE PROXIMITY TO DRY AIR IN THE MIDDLE LEVELS OF
THE ATMOSPHERE COULD INHIBIT DEVELOPMENT OF THIS DISTURBANCE. THIS
SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS...AND A MEDIUM CHANCE...50
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS
WHILE IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 10 TO 15 MPH OVER
THE CARIBBEAN SEA...AND NEAR OR OVER HISPANIOLA. REGARDLESS OF
WHETHER OR NOT A TROPICAL CYCLONE FORMS...LOCALLY HEAVY RAINFALL
AND STRONG GUSTY WINDS ARE EXPECTED TO AFFECT PORTIONS OF THE
LESSER ANTILLES THROUGH MONDAY.

OTHER SYSTEMS WITH FORMATION POTENTIAL BEYOND 48 HOURS...

A TROPICAL WAVE OVER THE NORTHWESTERN CARIBBEAN SEA IS FORECAST TO
MOVE ACROSS THE YUCATAN PENINSULA AND INTO THE BAY OF CAMPECHE IN A
COUPLE OF DAYS WHERE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO
BECOME MARGINALLY FAVORABLE FOR DEVELOPMENT. THIS SYSTEM HAS A LOW
CHANCE...NEAR 0 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS...AND A LOW CHANCE...20 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 5 DAYS...AS IT MOVES
WEST-NORTHWESTWARD AT 10 MPH.

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NHc says 40 % & 50 % at 8 pm TWO
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1430. IKE
Sorry for Hispaniola....but that could kill whatever it is.
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1429. JRRP
Quoting SLU:
...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED. LESSER ANTILLES THROUGH MONDAY.


FORECASTER PASCH

That's not what Stewart said at 2pm. The NHC forecasters aren't on the same page.

lol
Member Since: August 16, 2007 Posts: 0 Comments: 5748
1428. Walshy
I think this may be a good analog with the whole no hurricane theme this season..

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1427. SLU
...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED.

FORECASTER PASCH

That's not what Stewart said at 2pm. The NHC forecasters aren't on the same page.
Member Since: July 13, 2006 Posts: 12 Comments: 5066
1426. scott39
Quoting 1423. FunnelVortex:


Is it reliable?
No IMO
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Quoting 1398. nrtiwlnvragn:


There is another specialist as optimistic as Stewart?
Not that I've ever seen lol.
Member Since: September 2, 2009 Posts: 130 Comments: 21172
1424. JRRP
Quoting nrtiwlnvragn:
Big shift from 12Z






interesting
Member Since: August 16, 2007 Posts: 0 Comments: 5748
Quoting 1422. SFLWeatherman:
18Z


Is it reliable?
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18Z
Quoting 1419. FunnelVortex:


What Z is this?
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1421. scott39
Quoting 1419. FunnelVortex:


What Z is this?
12pm
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Quoting 1413. MAweatherboy1:
NHC took a very conservative tone on that TWO.



thanks two FORECASTER PASCH
Member Since: May 21, 2006 Posts: 5091 Comments: 114966
Quoting 1412. nrtiwlnvragn:
Big shift from 12Z







What Z is this?
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1418. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5748
Quoting 1373. ProphetessofDoom:
If I recall, Cuba does not always inhibit a storm's development. Wasn't there this little storm named Sandy that crossed Cuba and remained not only intact, but continued to slowly strengthen? So if 97l does develop and track across Cuba as some models have indicated, then there is no guarantee that it will be ripped apart!

Edit: that is of course if it develops at all!
Actually Cuba did a fairly good job of disrupting Sandy... max winds occurred just before it hit Cuba, and the resultant disruption kept the Bahamas from feeling Sandy's worst.
Member Since: October 25, 2005 Posts: 19 Comments: 21943
OTHER SYSTEMS WITH FORMATION POTENTIAL BEYOND 48 HOURS...

A TROPICAL WAVE OVER THE NORTHWESTERN CARIBBEAN SEA IS FORECAST TO
MOVE ACROSS THE YUCATAN PENINSULA AND INTO THE BAY OF CAMPECHE IN A
COUPLE OF DAYS WHERE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO
BECOME MARGINALLY FAVORABLE FOR DEVELOPMENT. THIS SYSTEM HAS A LOW
CHANCE...NEAR 0 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS...AND A LOW CHANCE...20 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 5 DAYS...AS IT MOVES
WEST-NORTHWESTWARD AT 10 MPH.
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting 1391. Civicane49:
Where..................................is the LLC...........................................,I'm tired to ask the same question.
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1414. scott39
Quoting 1411. FunnelVortex:


If it tracks into the gulf, we should be concerned. It could get interesting.
Low wind shear as of now.
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NHC took a very conservative tone on that TWO.
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Big shift from 12Z





Member Since: September 23, 2005 Posts: 14 Comments: 11122
Quoting 1404. LargoFl:
once it passes the small islands there is a spot that could weaken it some..then it gets under cuba and Bam..regeneration..


If it tracks into the gulf, we should be concerned. It could get interesting.
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Stays at 40% and 50%.
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting 1395. sunlinepr:
Its being hold by the interaction of the ULL over DR and the huge ULL in the north.... The thing is if it will develop under those conditions.... GFS doesnt shows any development yet....



The GFS can not always predict where and when the cane will form.
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1408. LargoFl
Quoting 1402. FunnelVortex:


We will have to wait and see. We could at least have a depression by then.
could be, i just dont see that yet
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1407. scott39
120/80
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I see 954FtLCane beet me to it, though. :)
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TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SUN SEP 1 2013

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

AN AREA OF LOW PRESSURE IS LOCATED NEAR THE LESSER ANTILLES.
SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THIS SYSTEM HAVE
DECREASED THIS EVENING...AND SURFACE OBSERVATIONS INDICATE THAT THE
CIRCULATION IS RATHER ELONGATED. ALTHOUGH UPPER-LEVEL WINDS APPEAR
TO BE CONDUCIVE...THE PROXIMITY TO DRY AIR IN THE MIDDLE LEVELS OF
THE ATMOSPHERE COULD INHIBIT DEVELOPMENT OF THIS DISTURBANCE. THIS
SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS...AND A MEDIUM CHANCE...50
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS
WHILE IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 10 TO 15 MPH OVER
THE CARIBBEAN SEA...AND NEAR OR OVER HISPANIOLA. REGARDLESS OF
WHETHER OR NOT A TROPICAL CYCLONE FORMS...LOCALLY HEAVY RAINFALL
AND STRONG GUSTY WINDS ARE EXPECTED TO AFFECT PORTIONS OF THE
LESSER ANTILLES THROUGH MONDAY.
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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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