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 165. LoneStarWeather:

Careful what you wish for. We are due for one to hit in Matagorda county this season. We have had one there every 5 years like clockwork for the last 40+ years. The last one to affect the area was Ike, in 2008.


No kidding. Well, if Gabs were to hit Freeport, that means Houston gets the "dirty quadrant" of the storm. San Antonio Bay looks fairly sparse. The goal is to get Texas wet without killing anybody. These intensity forecasts are getting interesting, if not ominous.
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000
NOUS42 KNHC 011535
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1100 AM EDT SUN 01 SEPTEMBER 2013
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 02/1100Z TO 03/1100Z SEPTEMBER 2013
TCPOD NUMBER.....13-092

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE LOW-LEVEL INVEST OF
CENTRAL CARIBBEAN SYSTEM NEAR 15.0N 72.0W FOR 03/1800Z.
3. REMARK: THE NASA 871 GLOBAL HAWK MAY FLY A 24-HOUR RESEARCH
MISSION OVER THE CARIBBEAN SYSTEM...TAKING OFF AT
03/1100Z.
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Quoting 200. Sfloridacat5:


The NHC have 97L at a 20% chance of organizing on thier site as of the 8am update.

Should be updatinng soon.


In 2 hours or less
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Glad to see you GROTHAR. I was worried. Now that you blobbed on the blog, I know all is well.

Where and how strong do you think 97L will be?
Member Since: March 10, 2006 Posts: 0 Comments: 10411
Lack of convergence will be a problem come DMIN. Poleward outflow is superb though, which at least shows that the system is breathing nicely at the moment.



And of course, as previously mentioned, the circulation is very elongated from east to west, along with the convective structure; with the 925mb vorticity maximum being located within the deepest convective activity just east of the Lesser Antilles.

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Quoting 180. Tazmanian:




the way 97L is going I think the NHC could vary well upgrade 97L too a TD or TS at any time has 97L has been Rapidly organizing




The NHC have 97L at a 20% chance of organizing on thier site as of the 8am update.

Should be updatinng soon.

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97L still has some work to do

I expect the NHC to up the chances to maybe 30 for the next 2 days and then 50 for the next 5 at 2pm
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Quote #170:

I know its hard to see but a MLC is developing at 15N/58W moving west around 15mph. The low level center is located at 60W now is a bit slower moving around 10mph so the two are about 2 degrees off which is resulting in some of the elongation. It will take another 4 hours before those can stack up and develop.

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Quoting 189. TWTracker99:
What will be 97L's percentage on the 2 PM TWO:

A. 0%
B. 10%
C. 20%
D. 30%
E. 40%
F. 50% and above


The NHC is generally conservative, so they'll probably give it 30%. Maybe 40%.
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Quoting 189. TWTracker99:
What will be 97L's percentage on the 2 PM TWO:

A. 0%
B. 10%
C. 20%
D. 30%
E. 40%
F. 50% and above
I'm going to go out on a limb and say E. 40%
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Quoting 165. LoneStarWeather:

Careful what you wish for. We are due for one to hit in Matagorda county this season. We have had one there every 5 years like clockwork for the last 40+ years. The last one to affect the area was Ike, in 2008.


1-2 punch? The NW Carib system looks like it's ours.. really strange seeing NHC unmoved and unconcerned by 97L while publishing those intensity forecasts.
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Quoting 189. TWTracker99:
What will be 97L's percentage on the 2 PM TWO:

A. 0%
B. 10%
C. 20%
D. 30%
E. 40%
F. 50% and above



30% next 48hrs 70% the next 5 days
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Quoting 189. TWTracker99:
What will be 97L's percentage on the 2 PM TWO:

A. 0%
B. 10%
C. 20%
D. 30%
E. 40%
F. 50% and above

D or E
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Quoting 134. 62901IL:

Maybe a depression already?


If it continues...its getting that look about it...something tells me that the sat appearance will look extremely better within 3-6 hours once the old vort completely dissipates and everything is allowed to flow to the dominate llcoc...convection has to continue for several hours for the lower levels to get strong enough to survive dmin tonight...also...did you see the updated cimss map...the anticyclone out to the east around 45w is for the wave behind it...but, it has its own weak anticyclone....directly over the coc...

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Quoting 188. Grothar:
Yes, Virginia, there are blobs!






there you are I new you come out of hiding some day
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190. SLU
Quoting 159. RascalNag:


With that kind of upper divergence, rather quickly might be a slight understatement!


Hehe. But it's pulling together rather quickly in truth
Member Since: July 13, 2006 Posts: 13 Comments: 5253
What will be 97L's percentage on the 2 PM TWO:

A. 0%
B. 10%
C. 20%
D. 30%
E. 40%
F. 50% and above
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Yes, Virginia, there are blobs!



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Quoting 137. SLU:
Finally the season is getting out of neutral gear.

Too bad its geared for landfalls. Maybe K.O.T.G. can fan them out towards the Atlantic.
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Very broad and elongated circulation from SW to NE
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Good Morning everybody.
Here in Guadeloupe, little wind & little rain for the moment.
Here is the link to a webcam in St François Guadeloupe. View of the laggoon. http://www.plage-guadeloupe.fr/index.php/la-webca m
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97L/INV/XX/XX
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Quoting 179. BCastro:
This system could very well catch many people off guard here in the states considering the lack of activity this year.


Good point there.
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Quoting 177. wxgeek723:
Guys this thing is an invest, calm down LOL.

By the way, until the system is renumbered and upgraded to a tropical storm, please refrain from calling it Gabrielle.


That's right, we are now on the g-spot. It's been so long I forgot.
Member Since: March 10, 2006 Posts: 0 Comments: 10411
Quoting 175. MiamiHurricanes09:
And of course, ASCAT missed.



We need QuickScat badly.
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Quoting 169. wunderkidcayman:
Updated flight plan USAF RECON flyin into 97L on Tueday and a NASA UAV will fly same time




the way 97L is going I think the NHC could vary well upgrade 97L too a TD or TS at any time has 97L has been Rapidly organizing


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This system could very well catch many people off guard here in the states considering the lack of activity this year.
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You can see the old COC dying out to the west of the one that's taking over...
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Guys this thing is an invest, calm down LOL.

By the way, until the system is renumbered and upgraded to a tropical storm, please refrain from calling it Gabrielle.
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Quoting 175. MiamiHurricanes09:
And of course, ASCAT missed.



shocker.
Member Since: March 10, 2006 Posts: 0 Comments: 10411
And of course, ASCAT missed.

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174. LBAR
Isn't this the wave the Navy model last week predicted would develop, but we were told that forecast was "dubious" because of all the dry air?
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Quoting 158. PedleyCA:
Best way to get something to develope is try to take a few days off. Thanks for the update Doc,

agree 100%!

Was enjoying dry conditions here in Nashville region.. gonna do some yard work over the holiday... NOT.. wokeup this mornin' to the sound of (you know what)
Raining all morning with more heading this way from from the NW.. have a great weekend everyone!
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Quoting 129. Patrap:

oh my. I personally think 97L will develop. Whether it becomes as strong as the models say idk
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Tropical Update:

Link
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Am I the only one seeing some slight mid level rotation?

Whether there is or isn't an MLC though, I think we're in the final countdown to liftoff for 97L...
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Updated flight plan USAF RECON flyin into 97L on Tueday and a NASA UAV will fly same time
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Quoting 164. GTstormChaserCaleb:
Pulled from an AMS Journal

Abstract: "The global convective diagnostic (GCD) is a bispectral (infrared and water vapor), day–night scheme for operationally mapping deep convection by means of geostationary satellite images..."

Link

Deep Convection and stronger thunderstorms, probably towering thunderstorms rising up to the top of the atmosphere. Something like that is my interpretation. :)

Thanks!
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Station 41300
Meteo France
Location: 15.850N 57.467W
Date: Sun, 01 Sep 2013 15:00:00 UTC



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I do not like the mode runs for 97L this could be bad for any one on the gulf coast
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Quoting 136. slavicthunder:


Somewhere around Matagorda Bay looks like a decent place for a landfall. Relatively sparse population. As long as the strongest winds can stay out of the large metropolitan areas.

Careful what you wish for. We are due for one to hit in Matagorda county this season. We have had one there every 5 years like clockwork for the last 40+ years. The last one to affect the area was Ike, in 2008.
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Quoting 151. 62901IL:

What're the reds?
Pulled from an AMS Journal

Abstract: "The global convective diagnostic (GCD) is a bispectral (infrared and water vapor), day–night scheme for operationally mapping deep convection by means of geostationary satellite images..."

Link

Deep Convection and stronger thunderstorms, probably towering thunderstorms rising up to the top of the atmosphere. Something like that is my interpretation. :)
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Quoting 158. PedleyCA:
Best way to get something to develope is try to take a few days off. Thanks for the update Doc,


Better get the Plutonium P-235 ready, pedley.
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Quoting 126. Seflhurricane:
97L is very close to TD status all that is missing is a well defined llc , i expect the nhc to bump development chances to 60% at 2pm
This is like saying 97L is an elephant, and all it's really missing is a trunk.
.
One or 2 of you seem to maybe be a bit ahead of the situation.
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Quoting 151. 62901IL:

What're the reds?
I believe is strong convection.
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Quoting 124. SLU:


You are right. The air is rushing into the large blob east of Martinique indicating that the pressures are lowering rather quickly there as a dominant low starts to consolidate there. Would love to have a recon investigate this today but .. oh well...



With that kind of upper divergence, rather quickly might be a slight understatement!
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Best way to get something to develope is try to take a few days off. Thanks for the update Doc,
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the wind has picked up in the past 10 to 15 minutes here in dominica... there is some light rain falling but nothing compared and some heavier stuff is expected later.
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Quoting 149. GTstormChaserCaleb:
Convective Diagnostic Satellite Imagery over 97L showing lots of reds:





this is not good
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Quoting 145. Tazmanian:
97L could be are 1st CAT 3 hurricane of the season may be even cat 5 if wind shear is right

Horrid.thought
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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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