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 246. QPhysFTW:
Is 97L really lacking in surface convergence? I look at the cumulus motions in this visible sat image, and it looks to me like there's broad scale W/WSW motion south of the disturbance and rapid E/ENE motion north of it.

Seems like it's piling up air nicely to me!



I agree. The convergence readings from the 1500 UTC maps are probably already useless in my opinion; the lower level clouds indicate a significant change in low level structure over the past hour or so.
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Quoting 252. HurricaneHunterJoe:


But is is Warning? Will Robinson
Why don't sheep shrink when it rains?
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A lot of divergence associated with 97L.


Decent amount of convergence associated with it as well. Supports continued thunderstorm activity for now.
Member Since: July 8, 2005 Posts: 259 Comments: 24039
Quoting 188. Grothar:
Yes, Virginia, there are blobs!





But is it Warning? Will Robinson
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Quoting 247. CybrTeddy:
It'll be interesting to see just how poor the models are doing this year if both the GFS and ECMWF miss a major storm. Not saying 97L will develop, but it will give a well earned egg into the face of everyone who treats those models like gospel.


Yeah, I wunder who dat is?

; 0
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238. SuperStorm093 4:18 PM GMT on September 01, 2013

One should be careful when using the words NEVER and ALWAYS when it comes to tropical weather forecasting
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How was I a troll right there, I gave reasons. I am not a downcaster, I just say what is going on. Look at how my forecast so far have been this year, I never wishcasted like some who predicted maybe 2-3 hurricanes that never happened.
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It'll be interesting to see just how poor the models are doing this year if both the GFS and ECMWF miss a major storm. Not saying 97L will develop, but it will give a well earned egg into the face of everyone who treats those models like gospel.
Member Since: July 8, 2005 Posts: 259 Comments: 24039
Is 97L really lacking in surface convergence? I look at the cumulus motions in this visible sat image, and it looks to me like there's broad scale W/WSW motion south of the disturbance and rapid E/ENE motion north of it.

Seems like it's piling up air nicely to me!

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I gotta get ready for work... I will check in later and see what the latest runs say 97L should be up to.

Enjoy your labor day weekend!
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Quoting 237. 62901IL:

OK, we have 97L then and that is it.



96L has 0% ch of forming that why said it dos not have a ch right now
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Levi Cowan ‏@TropicalTidbits 21m
Westerly winds at Barbados are strengthening, now up to 16kt. 97L is becoming a tighter system, but still elongated.
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Without the Euro and GFS this is really going to have to prove itself. Anticyclone might help it do that.
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Quoting 232. Walshy:


The upcoming phase 1 (and perhaps 2) MJO is projected to be 2nd strongest (~2.40 per Euro) and tied for the 2nd longest at 1.50+ (8/28-9/7 or 11 days per Euro) of any phase 1 and 2 near the peak of the hurricane season since 1975.

-GaWx


THANKS. So this could be interesting now.

I hope no Major hits to a populated areas, though.
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Quoting 221. hydrus:
What do you think will happen with this system in the next three days.?


It is going to take a bit to even get organized, its to elongated. I need to see it survive DMIN with a good structure and good tstorms. IF it cant do that, this will never become a hurricane.
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Quoting 233. Tazmanian:



you can drop 96L from you list

OK, we have 97L then and that is it.
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Guess the trolls have woken up, already 3 quotes on one troll.
Member Since: July 8, 2005 Posts: 259 Comments: 24039
235. VR46L
Quoting 212. SuperStorm093:
Listen, it has nothing at the mid-levels, no closed circulation, lack of convergence, I could go on and on here. I am not downcasting, but the fact that it is September 1st and we are going crazy over an invest that has its highs and lows is laughable.


I agree with you but it appears to be an unpopular point of view ..

Even the NHC and the major models are not really interested ...
Member Since: March 1, 2012 Posts: 0 Comments: 6901

Hey, has anyone noticed that 96L is also doing quite well to get its act together...albeit a bit slowly but it too has been firing more deep convection with a way better defined spin and circulation at the mid and lower levels (compared to 97L). There should be no doubt here of a closed off low level center of circulation. The NHC May have written it off with Lower percentage probablities a tad too early & Forcaster Stewart et Al. IMO...
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Quoting 228. 62901IL:

hahahahahahahaha...they really are not paying attention. We have 96L and 97L...or do they not know?



you can drop 96L from you list
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Quoting Dakster:


And we are currently at what?


The upcoming phase 1 (and perhaps 2) MJO is projected to be 2nd strongest (~2.40 per Euro) and tied for the 2nd longest at 1.50+ (8/28-9/7 or 11 days per Euro) of any phase 1 and 2 near the peak of the hurricane season since 1975.

-GaWx
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Quoting 210. Sfloridacat5:
The NHC puts quite a bit of trust in the GFS model. I'm waiting to see when the GFS picks up the system.

Be interesting to see if the 12z GFS picks up 97L(which NAM picked up on 4 days ago).


It fails to develop 97L, a little more enthusiastic about the wave behind it.
Member Since: July 8, 2005 Posts: 259 Comments: 24039
Quoting 225. Dakster:
Who posted a virus/Trojan? I am getting security flags from the site now.



same here I ues IE 10
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Quoting 226. 62901IL:

What browser are you using?


IE right now. Usually I used FireFox or Chrome, but I haven't installed them on this box.
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Quoting 224. Sfloridacat5:
The hurricane expert for the TWC just said "there's nothing going on right now in the tropics."


hahahahahahahaha...they really are not paying attention. We have 96L and 97L...or do they not know?
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Quoting 221. hydrus:
What do you think will happen with this system in the next three days.?



LOL good luck of getting a good forcast from him he downcast evere thing he sees
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Quoting 225. Dakster:
Who posted a virus/Trojan? I am getting security flags from the site now.

What browser are you using?
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Who posted a virus/Trojan? I am getting security flags from the site now.
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The hurricane expert for the TWC just said "there's nothing going on right now in the tropics."

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Quoting 212. SuperStorm093:
Listen, it has nothing at the mid-levels, no closed circulation, lack of convergence, I could go on and on here. I am not downcasting, but the fact that it is September 1st and we are going crazy over an invest that has its highs and lows is laughable.


you are downcasting big time
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Quoting 212. SuperStorm093:
Listen, it has nothing at the mid-levels, no closed circulation, lack of convergence, I could go on and on here. I am not downcasting, but the fact that it is September 1st and we are going crazy over an invest that has its highs and lows is laughable.
What do you think will happen with this system in the next three days.?
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Quoting 210. Sfloridacat5:
The NHC puts quite a bit of trust in the GFS model. I'm waiting to see when the GFS picks up the system.

Be interesting to see if the 12z GFS picks up 97L(which NAM picked up on 4 days ago).


It didnt, not even a cloud of 97L is noticed on the 12Z GFS
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219. VR46L


Ascat missed !



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97L is a elongated area of low pressure around 1009mbs.... we need to see:

1. N winds

2. Consolidation of T-Storms near the N winds to increase them with some pressure falls.

3. Persistance through the day and night tonight.

I give it a 30% chance of development in 24hrs 50% after in 48hrs then if it's not developed by Monday night, it will have to wait another day or 2 until it gets near Jamaica.
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I thought I heard Gro's voice... Did I?
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Quoting 211. Walshy:
GaWx from AmericanWx

10 Strongest MJO phase 1, 2 peaks during 8/21-9/20 since 1975: TC geneses when MJO 1.50+ in phase 1 or 2 that later became H’s

-3.08 peak 8/28/79: cat 5 David, cat. 4 Frederic, cat 2 Gloria
-2.21 peak 9/5/81: cat 1 Emily, cat 3 Floyd, cat 2 Gert
-2.07 peak 9/19/89: none
-2.01 peak 9/4/83: cat 1 Chantal
-2.01 peak 9/20/04: cat 1 Lisa
-1.98 peak 8/23/99: cat 2 Dennis
-1.92 peak 8/26/11: none
-1.90 peak 8/29/07: cat 5 Felix
-1.89 peak 8/30/88: cat 1 Debby
-1.88 peak 8/23/08: cat 4 Gustav

So, there were geneses of TC’s during these 10 strongest amplitude periods in phases 1 and 2 that later became 12 H’s (5 major) and these resulted in TC’s during 8 of the 10 periods that later became H’s.
Three hit the US as a H, two of them being major H hits.


And we are currently at what?
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I agree with WXGEEK. There needs to be persistence shown with this before jumping to conclusions. Sometimes \the AOIs look like hurricanes before we get an upgrade.
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20-30% seems like a good assessment to me for the next 48 hours. Invest 97L has become better organized, there's no doubt about that, but it is still very broad in nature and pretty disorganized. The trade wind flow in the eastern Caribbean, while about average, is still too quick to allow for tropical development while the system is there. Once the storm passes south and west of Hispaniola, we may see real development there.
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Listen, it has nothing at the mid-levels, no closed circulation, lack of convergence, I could go on and on here. I am not downcasting, but the fact that it is September 1st and we are going crazy over an invest that has its highs and lows is laughable.
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GaWx from AmericanWx

10 Strongest MJO phase 1, 2 peaks during 8/21-9/20 since 1975: TC geneses when MJO 1.50+ in phase 1 or 2 that later became H’s

-3.08 peak 8/28/79: cat 5 David, cat. 4 Frederic, cat 2 Gloria
-2.21 peak 9/5/81: cat 1 Emily, cat 3 Floyd, cat 2 Gert
-2.07 peak 9/19/89: none
-2.01 peak 9/4/83: cat 1 Chantal
-2.01 peak 9/20/04: cat 1 Lisa
-1.98 peak 8/23/99: cat 2 Dennis
-1.92 peak 8/26/11: none
-1.90 peak 8/29/07: cat 5 Felix
-1.89 peak 8/30/88: cat 1 Debby
-1.88 peak 8/23/08: cat 4 Gustav

So, there were geneses of TC’s during these 10 strongest amplitude periods in phases 1 and 2 that later became 12 H’s (5 major) and these resulted in TC’s during 8 of the 10 periods that later became H’s.
Three hit the US as a H, two of them being major H hits.
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The NHC puts quite a bit of trust in the GFS model. I'm waiting to see when the GFS picks up the system.

Be interesting to see if the 12z GFS picks up 97L(which NAM picked up on 4 days ago).
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Northern Hemisphere ACE

To Date:

121.16

Avg to Date:

256

Click to ZOOM


Just a bit of warm water in the NW Caribbean:

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208. SLU
Quoting 187. hydrus:
Too bad its geared for landfalls. Maybe K.O.T.G. can fan them out towards the Atlantic.


Yup. She's primed to be a real trouble maker later in the week. The season is about to begin.
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Quoting 149. GTstormChaserCaleb:
Convective Diagnostic Satellite Imagery over 97L showing lots of reds:



Link this, please, GT. TIA
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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.




%20 is way to low now %30 for the next 48hrs 70% for the next 5 days seem likey at the next two
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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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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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