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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I see, blog has something to track and will be happy, at least unless havoc is looming (hope not!, though I'm suspicious 97L will mean no good down the road). So no need for me to fill in with European weather for a while, unless something really dramatic is happening. And a busy week for me in office lies ahead anyway.

I'll follow your fate over there, and whish you a nice Sunday from intermittently quite chilly Germany as a trough from the UK is moving in:

Member Since: October 25, 2008 Posts: 62 Comments: 6697
I'd like to say however, those fairly strong west winds seem to be a good indicator this may not be another Chantal or Dorian.
Member Since: January 1, 2008 Posts: 0 Comments: 3798
It looks like the GFS has 97L going over Hispanola, and that is one reason it does not develop it.
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Quoting 261. Gearsts:
Look at the winds on the north side and on the southside speeding up


Definitely looks like it trying to spin up. What concerns me is the wind shear blowing the top of the convection off to the north.
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Quoting 295. KEEPEROFTHEGATE:
trying to fine it taz not sure which one it is



seems too be gone now
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I'm out for a bit.
Be Back Later.
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Quoting 290. eddiedollar:
18mph westerlies coming out of Barbados.



Peeps, everyone knows and can see there are West winds... What we need to find is North winds and not 250 miles away from the middle of the elongated center. If there are N winds around 15N and 57-59W then we might have something if it can keep T-Storms going into and through the night.
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Quoting 255. RascalNag:


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.


Lower convergence depicted by the CIMSS is not 100% accurate. I remember it showing no convergence for Fernand when it was close to developing and some said it might lose all of its convection during DMIN. When it develop and the map updated it show a lot of convergence again. A inconsistent map IMO. Satellite imagery is usually the best. You can clearly see air accelerating to the south and feed the intense convection.
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Quoting 254. PalmBeachWeather:
Why don't sheep shrink when it rains?
I don't know. Why don't sheep shrink when it rains?
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Quoting 268. Levi32:
So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.


Just perhaps, kudos on 97. Good call.
Member Since: January 1, 2008 Posts: 0 Comments: 3798
Quoting 286. Tazmanian:



some one posted a virus/Trojan? I am getting security flags from the site now


I ues IE 10 and seeing se certificate errors pop up on IE 10 have you modes been able too find that post and re move it?
trying to fine it taz not sure which one it is
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294. whitewabit (Mod)
Quoting 291. SuperStorm093:
Why aren't you calling some of the other guys that just LITERALLY said the same things I

Monomania .. excessive concentration on a single object or idea
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Quoting 268. Levi32:
So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.


FWIW, seems to me the CMC had a good idea of the current organization. Correctly analysis a surface low.
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Why aren't you calling some of the other guys that just LITERALLY said the same things I said a troll or downcaster?
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18mph westerlies coming out of Barbados.
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wishcasting what been nothing to wish cast in the first place

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Quoting 276. washingtonian115:
If this was the 2004,2005,2008,and 2010 hell even the 2011 season I would be a little more concerned with 97L ....but I'm not.Especially seeing how bad the storms have been struggling this year..Perhaps the GFS finally realizes like the Euro it wants quality over quantity.


Problem with that kind of thinking is that it is how people get caught off guard. Just because nothing of significance has formed this season, does not mean we cant have a major hurricane or a storm that causes a lot of problems before the season is out.

You look at storms on an individual basis and not in conjunction with the season as a whole.
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Quoting 264. KEEPEROFTHEGATE:


quit lying you come here see good discussion but go out of your way to cause a riff among the bloggers and downcast everything to suit your motives to discredit people on the blog and be an overall nuisance

you blow your horn too much
and push your downcasting agenda on everyone here if ya don't like what we do here or talk about go someqhere else



some one posted a virus/Trojan? I am getting security flags from the site now


I ues IE 10 and seeing se certificate errors pop up on IE 10 have you modes been able too find that post and re move it?
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Quoting 279. TropicalAnalystwx13:

Or maybe not so clear.


Oh sorry :p I didn't look at the satellite
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Quoting 268. Levi32:
So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.



Hey Levi, I have seen your YouTube tropical tidbits and they are very easy to understand. You have even inspired me to do my first tropical update as well. To see it click here: Link. Thanks for making everything so easy to understand! Anyway, what is your thinking of 97L right now? Do you think it will be Gabrielle?
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Quoting 207. moonlightcowboy:


Link this, please, GT. TIA
Latest Satellite Imagery from ERAU
Member Since: June 30, 2013 Posts: 12 Comments: 8774
Quoting 268. Levi32:
So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.


In other words Levi believes we should start looking now for new female G names.

:)
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Quoting 264. KEEPEROFTHEGATE:


quit lying you come here see good discussion but go out of your way to cause a riff among the bloggers and downcast everything to suit your motives to discredit people on the blog and be an overall nuisance

you blow your horn too much
and push your downcasting agenda on everyone here if ya don't like what we do here or talk about go someqhere else


Keep it going, VRL just agreed with what I said. Its not called downcasting, its called reality. I forecast in the moment and not in the next coming days. That is how I do it, if I see it becoming organized then I will be good. But you guys have been wishcasting all year and hasnt worked out now has it?
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Quoting 270. Hurricanes101:


Greatest Post Ever


x100!
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Quoting 267. Doppler22:

ummmmmmmm... Clearly stronger then NHC says

Or maybe not so clear.

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Link
Quoting 243. Gearsts:
Levi Cowan %u200F@TropicalTidbits 21m
Westerly winds at Barbados are strengthening, now up to 16kt. 97L is becoming a tighter system, but still elongated.
As I pointed out earlier...bout time!! :)
http://www.surfline.com/surf-report/soup-bowl-bar bados_5555/
Skys darkening on visual.
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If this was the 2004,2005,2008,and 2010 hell even the 2011 season I would be a little more concerned with 97L ....but I'm not.Especially seeing how bad the storms have been struggling this year..Perhaps the GFS finally realizes like the Euro it wants quality over quantity.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting 264. KEEPEROFTHEGATE:


quit lying you come here see good discussion but go out of your way to cause a riff among the bloggers and downcast everything to suit your motives to discredit people on the blog and be an overall nuisance

you blow your horn too much
and push your downcasting agenda on everyone here if ya don't like what we do here or talk about go someqhere else

Best. Post. Ever.
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Quoting 269. RascalNag:
Any recon scheduled for 97L?
not today
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A Mature CV seed needs careful scrutiny..esp if it has travel plans w, by nw.


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Outflow is becoming more apparent as the ULL is help it to breathe rather than shearing it. The old circulation to the SW is stretching out the circulation but the LLC is becoming better organized with westerlies now at 16kts (per Levi tweet). It would not surprise me in the least if it get renumbered overnight.


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Quoting 264. KEEPEROFTHEGATE:


quit lying you come here see good discussion but go out of your way to cause a riff among the bloggers and downcast everything to suit your motives to discredit people on the blog and be an overall nuisance

you blow your horn too much
and push your downcasting agenda on everyone here if ya don't like what we do here or talk about go someqhere else


Greatest Post Ever
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Any recon scheduled for 97L?
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So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.
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Quoting 218. Stormchaser2007:

ummmmmmmm... Clearly stronger then NHC says
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Still looks pretty stretched currently. It's certainly made leaps and bounds since I awoke, but it's nowhere near being worthy of depression status. I have no doubt there are likely winds that would support it, but for the time being, it's got a ways to go.

Some cold cloud tops and persistent convection.




It seems it keeps trying to shake its western periphery of low pressure, kind of back-building.
Member Since: January 1, 2008 Posts: 0 Comments: 3798
Quoting 248. SuperStorm093:
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.


quit lying you come here see good discussion but go out of your way to cause a riff among the bloggers and downcast everything to suit your motives to discredit people on the blog and be an overall nuisance

you blow your horn too much
and push your downcasting agenda on everyone here if ya don't like what we do here or talk about go someqhere else
Member Since: Posts: Comments:
96L has a 10% of becoming a tropical cyclone with the next 5 days as per the NHC.

2. A WEAK AREA OF LOW PRESSURE ASSOCIATED WITH A TROPICAL WAVE IS
LOCATED JUST TO THE EAST OF THE NORTHERN CAPE VERDE ISLANDS.
ASSOCIATED SHOWER AND THUNDERSTORM ACTIVITY HAS CONTINUED TO
DECREASE...AND ENVIRONMENTAL CONDITIONS DO NOT APPEAR 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...10 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 5 DAYS.
..AS IT MOVES GENERALLY WEST-NORTHWESTWARD OVER THE
EASTERN ATLANTIC.
Member Since: September 30, 2008 Posts: 0 Comments: 108
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Look at the winds on the north side and on the southside speeding up
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BTW I am not saying this couldnt become a pretty bad storm, it very well could and this, in my opinion is the best shot all year, it just has to get organized.
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Levi is up now!:)
This is from Levi
Invest 97L is moving slowly through the lesser Antilles islands and is generating more deep thunderstorms than yesterday. As expected, the models are underestimating the organization of 97L, and its chances of eventually developing into a tropical depression are decent, despite no reliable models showing development. 97L's organization will likely be a gradual process as it moves slowly through the Caribbean. Regardless of development, heavy rain and strong winds will impact the lesser Antilles over the next couple of days.
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Quoting 186. Stormchaser2007:
Very broad and elongated circulation from SW to NE
I have seen worse. Should be able to pull that together.
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Quoting 218. Stormchaser2007:
Its a hurricane.
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Quoting 198. Hurricanes305:
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.



Looks to be organizing?
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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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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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