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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Lots of models are moving back some east than before


\
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97L is very near TD status now IMO.



20knot due wind winds out of Barbados.
Member Since: April 29, 2007 Posts: 0 Comments: 7692
I know the main focus is on Invest 97L, and probably rightfully so, but let's not forget to watch the sharp tropical wave axis currently moving into the Yucatan. It's forecast to enter the Bay of Campeche late tomorrow, where atmospheric conditions will be at least marginally conducive for tropical cyclone development. As we saw with Fernand, systems like to go to town down here given the opportunity. While I haven't seen a model that develops it, the NHC is giving this wave a 20% chance of developing within 5 days.

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Quoting SLU:
The circulation is closed.

Barbados

3:00 PM 82.4 °F 94.0 °F 80.6 °F 94% 29.80 in 6.2 mi NNW 6.9 mph - N/A Mostly Cloudy

Winds have been W-WSW all day here in Trinidad.
Made for a Beautiful day !
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Quoting 749. taco2me61:


Houston we may have a Problem :o(

Taco :o(

Nice switching of Emoticons.
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Quoting 747. DonnieBwkGA:
The eastern Caribbean is usually not very good for storms to organize in. Are there any reasons why that may not be the case now?


Nope.
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Quoting 724. CybrTeddy:
GFDL ensembles.


Houston we may have a Problem :o(

Taco :o(
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HWRF and GFDL take this NW. if the GFS and euro are wrong this could mean trouble. all it takes is one storm.
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The eastern Caribbean is usually not very good for storms to organize in. Are there any reasons why that may not be the case now?
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Wind shear has decreased quite a bit today in the Caribbean in preparations for 97L arrival.

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Quoting 718. EricfromJax:
How do I make everyone's post appear and to unhide all of them?

Eric
Look for the filter at the top right hand side of the comments box. Set to [Show All].... or any other setting you prefer.

If you put someone on ignore, you have to go to your blog to clear your ignore list.
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744. SLU
The circulation is closed.

Barbados

3:00 PM 82.4 °F 94.0 °F 80.6 °F 94% 29.80 in 6.2 mi NNW 6.9 mph - N/A Mostly Cloudy
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Not bad:
Member Since: July 8, 2005 Posts: 259 Comments: 23616
Member Since: July 3, 2005 Posts: 421 Comments: 127636
OK, I'm a little surprised at 97 this afternoon.
Didn't think it could pull this off today !

Still has some issues to deal with in the next 48 hrs or so, but right now it looks pretty good.

Could very well be something of concern down the road a bit.
Member Since: October 24, 2005 Posts: 0 Comments: 24060
Quoting 729. will40:


look right above the start of comment section. on the right you will see filter.choose see all.


Thanks Will
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Quoting 539. wunderkidcayman:
This is where NHC think 97L will be in 72hrs


That's not a good place for it to be !
Member Since: April 29, 2007 Posts: 0 Comments: 7692
Quoting 721. hurricane23:


First time we might not be dealing with a complete wimp, huh?
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Overall convection has warm some but the low level convective banding has really increased on the SE part of the system since 12 noon and moving quickly west and should meet up with the slow moving LLC by this evening (peak of DMIN).



Its organizing is not done for the rest of today by a longshot.
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Quoting 717. WxGeekVA:
This is how I'm seeing 97L right now: A surface low is there and is tightening up, but is still elongated. Now that environmental conditions are better, we should see development over the next 3 days.


Hey Geek, Long time no see.
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Quoting 718. EricfromJax:
How do I make everyone's post appear and to unhide all of them?

Eric
At the top of the comments section there is a filter. Select show all.
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.
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Quoting 724. CybrTeddy:
GFDL ensembles.



good news for Haiti bad news for the gulf coast
Member Since: May 21, 2006 Posts: 5091 Comments: 114760
732. whitewabit (Mod)
Quoting 718. EricfromJax:
How do I make everyone's post appear and to unhide all of them?

Eric


Set your Filter at the top of the comments ..
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Quoting 727. nrtiwlnvragn:
Marine Weather Discussion

Excerpt:

ANOTHER TROPICAL WAVE EXTENDS FROM 19N57W TO 1012 MB LOW PRES
NEAR 14.5N60.5W TO 10N62W. NUMEROUS SHOWERS AND SCATTERED
TSTMS...ALONG WITH SQUALLS ARE OCCURRING ACROSS THE WATERS FROM
14N TO 17N E OF 65W. FRESH TO STRONG WINDS AND 8-9 FT SEAS ARE
ACCOMPANYING THE LOW/TROPICAL WAVE FROM 15N TO 20N E OF 61W. THIS
LOW AND WAVE ARE FORECAST TO MOVE INTO THE E CARIBBEAN BY LATE
THIS AFTERNOON...WITH THE TROPICAL WAVE WEAKENING AS IT REACHES
THE CENTRAL CARIBBEAN BY TUE MORNING. MEANWHILE THE LOW IS
FORECAST TO DISSIPATE BY THEN WHICH WOULD BE IN AGREEMENT WITH THE
GFS AND ECMWF MODEL SOLUTIONS. THE UKMET AND CMC MODELS CONTINUE
TO SHOW QUITE A DIFFERENT SCENARIO WITH BOTH OF THOSE MODELS
DEVELOPING A TC WITH A W-NW MOVEMENT THROUGH THE WEEK. WILL
CONTINUE TO FOLLOW THE MUCH MORE CONSERVATIVE GFS/ECMWF SOLUTIONS
WHICH ARE IN LINE WITH THE OFFICIAL NHC THINKING AT THIS POINT.
THAT BEING SAID...WINDS ARE FORECAST TO DIMINISH TO 20 KT OR LESS
WITH SEAS SUBSIDING TO LESS THAN 8 FT BY TUE MORNING WITH THEN
MAINLY MODERATE WINDS AND 5-6 FT SEAS ASSOCIATED WITH THE WAVE AS
IT PROGRESSES THROUGH THE BASIN THIS UPCOMING WEEK.




The NHC thinks it'll dissipate, and they're giving it a 40/50% chance.
Member Since: July 8, 2005 Posts: 259 Comments: 23616
Quoting 724. CybrTeddy:
GFDL ensembles.

I know it hasn't formed yet and I might get yelled at for saying this but, I think the Gulf States need to keep a close eye on this
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Quoting 718. EricfromJax:
How do I make everyone's post appear and to unhide all of them?

Eric


look right above the start of comment section. on the right you will see filter.choose see all.
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Uploaded on Aug 31, 2008


This was the first wave of Gustav hitting the French Quarter in New Orleans. At the end you can see the speed the storm clouds are coming in and hear the wind picking up.

Tourist view of empty street as the outer band arrives in NOLA.


She gets spooked at the first big gust at the end.




Member Since: July 3, 2005 Posts: 421 Comments: 127636
Marine Weather Discussion

Excerpt:

ANOTHER TROPICAL WAVE EXTENDS FROM 19N57W TO 1012 MB LOW PRES
NEAR 14.5N60.5W TO 10N62W. NUMEROUS SHOWERS AND SCATTERED
TSTMS...ALONG WITH SQUALLS ARE OCCURRING ACROSS THE WATERS FROM
14N TO 17N E OF 65W. FRESH TO STRONG WINDS AND 8-9 FT SEAS ARE
ACCOMPANYING THE LOW/TROPICAL WAVE FROM 15N TO 20N E OF 61W. THIS
LOW AND WAVE ARE FORECAST TO MOVE INTO THE E CARIBBEAN BY LATE
THIS AFTERNOON...WITH THE TROPICAL WAVE WEAKENING AS IT REACHES
THE CENTRAL CARIBBEAN BY TUE MORNING. MEANWHILE THE LOW IS
FORECAST TO DISSIPATE BY THEN WHICH WOULD BE IN AGREEMENT WITH THE
GFS AND ECMWF MODEL SOLUTIONS. THE UKMET AND CMC MODELS CONTINUE
TO SHOW QUITE A DIFFERENT SCENARIO WITH BOTH OF THOSE MODELS
DEVELOPING A TC WITH A W-NW MOVEMENT THROUGH THE WEEK. WILL
CONTINUE TO FOLLOW THE MUCH MORE CONSERVATIVE GFS/ECMWF SOLUTIONS
WHICH ARE IN LINE WITH THE OFFICIAL NHC THINKING AT THIS POINT.
THAT BEING SAID...WINDS ARE FORECAST TO DIMINISH TO 20 KT OR LESS
WITH SEAS SUBSIDING TO LESS THAN 8 FT BY TUE MORNING WITH THEN
MAINLY MODERATE WINDS AND 5-6 FT SEAS ASSOCIATED WITH THE WAVE AS
IT PROGRESSES THROUGH THE BASIN THIS UPCOMING WEEK.


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Quoting 721. hurricane23:



That would be a HORRIBLE outcome for Haiti
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Quoting 713. txjac:


Actually this is a great response for someone that is new ...simple explanation to be digested ...and then further researched.

True.
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GFDL ensembles.
Member Since: July 8, 2005 Posts: 259 Comments: 23616
723. txjac
Are annular hurricanes worse than "regular" hurricanes? I can see the difference ..but if they impact land is it the same as a "regular" one?
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Quoting 699. SuperStorm093:
Yes it very well could become a big time storm, but I want to see it survive tonight.

And I am weird? Btw learn to spell, you say every storm is going to be a CAT 5 lol.
Most of these fronts coming down on the east coast will quickly dissolve and high pressure to rebuild.7 day forecast from the Hurricane Center shows the low south of Cuba.
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Cody, Strikes again.
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Happy September 1st, fat invest 97L watching. Yep, keeping an eye on it.

And on this date - Conspicuously absent, ahem, from TWC's recent feature on Labor Day storms that ruined the holiday, today marks 5th anniversary Hurricane Gustav landfall in SE LA, on Labor Day Sep 1 2008... It sure as hell ruined mine!



Hurricane Gustav Peak data recorded Louisiana, Sep 1 2008 -

Highest winds reported at offshore platform below Louisiana was from Miss Canyon 803 / KCYD located 114 miles SE of Houma with 90 kts / 103.57 mph sustained, 108 kts / 124.28 mph gust.

Highest gusts recorded in coastal locations with two identical reports - from SW Pass PSTL1 NOAA station in Plaquemines Parish and Houma Navigation Canal DULL1 USGS station in Terrebonne Parish, both reported peak gust of 102 kts / 117 mph.

Highest wind gust officially reported over inland Louisiana after landfall was 94 mph (93.7) recorded at HUML1 station Houma, Terrebonne Parish.

Lowest pressure in SE Louisiana measured during Gustav was 951.6 mb recorded at DCLL1 Caillou Lake USGS station, however the NHC chose to use to Cocodrie LUMCON reading of 954.5 mb as lowest for landfalling intensity(?). Both stations in coastal Terrebonne Parish.



"Image shot about 30 min into worst onslaught of strongest NE to ENE/ESE veering winds, with gusts ranging locally from widespread 90-100 mph up to 110 mph in iso spots, as Gustav plowed across Terrebonne... straining trees to breaking point while shredding them (view facing WNW)... Image shot at relatively fast 1/500th sec @ F4, froze most motion - large limb lower left had just hit ground, from large pecan on right... it and other debris that appear "lying still" on ground were actually blowing across to the left - would have been a blur at slower shutter speed... Seriously bent 30 ft young pecan trees foreground... fallen limb splashing water in mid sect... while large 90-100 ft older pecans in background are losing large limbs and near toppling / breaking point..."

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How do I make everyone's post appear and to unhide all of them?

Eric
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This is how I'm seeing 97L right now: A surface low is there and is tightening up, but is still elongated. Now that environmental conditions are better, we should see development over the next 3 days.

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716. Relix
97L is actually pulling it out. WOw. I am surprised. Should bring lots of rain to PR on Tuesday. Don't expect much from it but then again Irene made me swallow my words in 2011
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Quoting 698. BrandenCordeiro:
Can someone explain to me what DMIN is?

Thanks :)

Diurnal minimum, DMIN, is a certain time of the afternoon (usually right around sunset) when the temperature difference between the ocean and the air is at its lowest point; this lowers instability. Solar heating warms the upper atmosphere and creates a "cap" (layer of stable air; used to forecast severe weather as well) for which thunderstorms are unable to penetrate.
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Quoting 709. BrandenCordeiro:


Thanks.. that makes sense...

But how come the convection goes up as the night goes on sometimes?


Because then you have the opposite and that is DMax what? just before sunrise?
Member Since: March 22, 2009 Posts: 43 Comments: 2064
713. txjac
Quoting 705. TylerStanfield:

Allow for someone else, to answer this question in further and with more accuracy. :)


Actually this is a great response for someone that is new ...simple explanation to be digested ...and then further researched.
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Quoting 694. kmanislander:


I took that into account, hence the words " if it does not fade away this afternoon " in my post.

Yes sir. I was just using your post as an example to the blog, of what needs to be taken into account.
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Quoting 666. JLPR2:
Reminds me of TS Emily in 2011, that one developed right over the Lesser Antilles, 97L is looking nice maybe it will try that.

Unless it falls completely apart.

I guess you mean Emily of the 7 centres...

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Member Since: July 3, 2005 Posts: 421 Comments: 127636
Quoting 701. weatherlover94:



It's when the sun goes down. When the sun goes down usually convection decreases


Thanks.. that makes sense...

But how come the convection goes up as the night goes on sometimes?
Member Since: August 16, 2013 Posts: 0 Comments: 45
Afternoon AFD about 97L from the San Juan NWS.

SHOWER ACTIVITY SHOULD BE MINIMAL OVERNIGHT. MOISTURE CIRCULATING
AROUND A HIGH PRESSURE AT 700 MB WILL MOVE ACROSS THE AREA FROM
THE NORTH ON MONDAY...INCREASING THE CHANCES OF SHOWERS...MAINLY
ACROSS THE NORTHEASTERN TWO THIRDS OF THE PUERTO RICO.

ON TUESDAY THE MOISTURE FROM THE WAVE WILL MOVE ACROSS THE
FORECAST AREA WITH SHOWERS AND THUNDERSTORMS. AT THIS TIME MODELS
DO NOT SHOW TROPICAL CYCLONE FORMATION THOUGH SATELLITE IMAGERY
SUGGESTS THAT THERE IS CERTAINLY SOME POSSIBILITY. NEVERTHELESS...
THE LOW PRESSURE THAT WOULD BE ITS SEED IS QUITE ELONGATED AT THIS
TIME AND IT IS ENTERING AN AREA THAT TYPICALLY WORKS AGAINST SUCH
FORMATION. THEREFORE WILL GO WITH THE CONSENSUS OF FORECASTERS
HERE...AND AT THE HURRICANE CENTER...AND THE MAJORITY OF THE
MODELS AND SHOW A STRONG TROPICAL WAVE PASSING TUESDAY AND TUESDAY
NIGHT...MAINLY SOUTH OF THE AREA. THIS WILL BRING HEAVY RAIN TO
MANY AREAS TUESDAY AND TUESDAY NIGHT. THE GFS SHOWS RELATIVE
HUMIDITY AT 850 MB WEAKENING ON WEDNESDAY ALTHOUGH IN GENERAL
MOIST FLOW CONTINUES FROM THE SOUTHEAST AND SOUTH AND SO NOW
EXPECT BEST RAINS ON TUESDAY. NOT WITHSTANDING...THERE IS A GOOD
POSSIBILITY THAT STRONG SHOWERS AND THUNDERSTORMS COULD CONTINUE
INTO WEDNESDAY. AT THIS TIME IT IS TOO EARLY TOO PUT OUT A FLASH
FLOOD WATCH DUE TO THE UNCERTAINTY OF THE DEVELOPMENT OF THE
TROPICAL WAVE PASSING THROUGH THE CARIBBEAN AND ITS PATH IF IT
DOES DEVELOP. WE WILL RE- EVALUATE THIS SITUATION ON MONDAY AND
DECIDE IF SUFFICIENT RAIN POTENTIAL EXISTS FOR FLASH FLOODING.
WOULD EXPECT MANY AREAS OF URBAN AND SMALL STREAM FLOODING TO
DEVELOP TUESDAY THROUGH WEDNESDAY WITH IMPROVEMENT ON THURSDAY.
Member Since: April 29, 2009 Posts: 75 Comments: 14057
Quoting 701. weatherlover94:



It's when the sun goes down. When the sun goes down usually convection decreases


And that is because at that point in the day there is less difference in temp between the surface and air,thus less lift potential?
Is that (in laymans terms) correct?
Member Since: March 22, 2009 Posts: 43 Comments: 2064
Looks like ECMWF wants to bring whatever is left of 96L across the Atlantic:


72 hours



120 hours
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Quoting 701. weatherlover94:



It's when the sun goes down. When the sun goes down usually convection decreases

Allow for someone else, to answer this question further and with more accuracy. :)
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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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