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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1855. GatorWX
Quoting 1820. GTstormChaserCaleb:
It has an expansive moisture field, so dry air will not be an issue or impediment to development, what will be though is the ULL over Hispaniola and the one north of it, we'll see if D-MAX will allow it to re-fire convection.



A circular cycle, through the night into tomorrow. If doesn't develop, it'll do it over again. Until it can build up and center a llc, all that convection means nothing. Dry air, imo, is an issue at a particular level. Not sure the height of it, but dry air imo seems to be a reason why it failed this evening. I'm pretty sure the wv you see north of it is up pretty high giving the illusion of a moist atmosphere. Show me a good layered or contrast map. We'll say what Master's says as I imagine he'll give a decent little analysis. I bet dry air is an issue. I just got home and am tired, so....



Member Since: January 1, 2008 Posts: 0 Comments: 2876
Quoting 1852. GTstormChaserCaleb:
hmm?



GFS on board now?
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Quoting 1845. RascalNag:
Although 97L is a lot weaker than it was earlier, at least we can see the lower levels better. Seems like an LLC may be situated at 15N, 58W.


last BEST Fix was : AL, 97, 2013090200, , BEST, 0, 140N, 607W
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hmm?

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She's a scary one....


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Quoting 1834. MiamiHurricanes09:
Now that 97L's stripped for us, we can take a look at the lower-level structure; and from what I can see...there isn't one.



Looks as if we have two, with one just being east of Martinique, and the other still located under the convection - what remains of it.
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Quoting 1831. WoodyFL:


im worried about the Lake O. Im in Florida and it could be a real problem if a large rainmaker went over it.

i know these change all the time but more models are showing a nw turn.






Just as long as they don't jump the gun again like they did with Ernesto. Many Many scenarios on the table, including dissipation of both the invest or a storm traversing the mountains. Or a track over Hispaniola and the Bahama's as portrayed below.

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Quoting 1821. WoodyFL:
I know from reading the blog that intensity is the hardest thing to predict but lots of models are showing a strong system. I dont know but it guess it has some peoples attention.



And the new WPTV met was saying the models weren't showing a named storm. He should look at this.
Member Since: October 8, 2008 Posts: 14 Comments: 4553
Quoting 1832. ProgressivePulse:
With a supposed center entering the Eastern Caribbean this hour 97L could be a snooze fest for the next day or two.



Agree, it still has a chance but not the one the current models are showing. Likely to move furhter W then expected and therefore if it developes could enter the GOM. To foar out to know at this point.
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In 24 hrs. ULL moving away towards Cuba.

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Although 97L is a lot weaker than it was earlier, at least we can see the lower levels better. Seems like an LLC may be situated at 15N, 58W.
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Quoting 1821. WoodyFL:
I know from reading the blog that intensity is the hardest thing to predict but lots of models are showing a strong system. I dont know but it guess it has some peoples attention.

We've had several systems this year look like that in intensity forecasts to never materialize.
Member Since: August 2, 2011 Posts: 0 Comments: 1881
Quoting 1837. TropicalAnalystwx13:

"M" represents medium, the depth of the system


And that would imply that it is extending into the mid-levels, am I correct?

Edit: Thanks for the link.
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Quoting 1831. WoodyFL:


im worried about the Lake O. Im in Florida and it could be a real problem if a large rainmaker went over it.

i know these change all the time but more models are showing a nw turn.






Look at it this way: if the situation wasn't quite so dire with Lake Okeechobee, you probably wouldn't think twice about model runs for a broad low pressure area.
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1841. KEEPEROFTHEGATE (Mod)
Quoting 1835. WoodyFL:
peak will be 96 hrs from now and again at 144 according to intensity models what ever peak that will be
Member Since: July 15, 2006 Posts: 170 Comments: 53623
Any chance this effects New England?
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Oh, Lord.. just getting in from work, what is this.. one llc and two other competing centers on top? Has 97L been acting annular again today? I see the intensity fcsts are still alarming...
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Quoting 1820.

People have been talking all day about dry air yet the system is right in the middle of high tpw, extending way out in front of it. So someones interpretation of graphics is off. Who has the correct analysis??
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Quoting 1828. daddyjames:


Not according to the last three ATCF fixes, showing it to be mid-level in organization

AL, 97, 2013090112, , BEST, 0, 140N, 590W, 30, 1008, LO, 0, , 0, 0, 0, 0, 1012, 200, 80, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 97, 2013090118, , BEST, 0, 140N, 597W, 30, 1008, LO, 0, , 0, 0, 0, 0, 1012, 200, 70, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 97, 2013090200, , BEST, 0, 140N, 607W, 30, 1008, LO, 34, NEQ, 0, 0, 0, 0, 1011, 200, 70, 0, 0, L, 0, , 0, 0, INVEST, M,

"M" represents medium, the depth of the system
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1836. JRRP
Quoting CaribBoy:
DMIN is really a pest :(

jajajjajajajja
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1835. WoodyFL
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Now that 97L's stripped for us, we can take a look at the lower-level structure; and from what I can see...there isn't one.

Member Since: September 2, 2009 Posts: 130 Comments: 21178
1833. beell
Quoting 1812. TropicalAnalystwx13:

Maybe if this was a better developed system. But 97L is a disorganized wave with little reflection higher than 850mb, meaning its track should be dictated by the low-level flow which is predominantly west, if not a little west-southwest. No?


Check the little "x" just east of the Lesser Antilles on the GFS frame @ #1796-a hint of a mid-level reflection. Also a decent mid-level reflection associated with the ULL north of 97L and atop the disturbance on the CIMSS 500 mb vort product.



And finally, the "tug of war" is an attempt to explain the current state of disorganization not so much a forecast track.

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With a supposed center entering the Eastern Caribbean this hour 97L could be a snooze fest for the next day or two.

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1831. WoodyFL
Quoting 1824. ProgressivePulse:


Looks like 97L has a rather high potential to be our first hurricane down the line.


im worried about the Lake O. Im in Florida and it could be a real problem if a large rainmaker went over it.

i know these change all the time but more models are showing a nw turn.




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Quoting 1827. wunderkidcayman:

Yep

D-Max starts in 2 hours and peaks at sunrise it surely going to be interesting
Let me go stand on the sidelines and go steal a couple of pom-poms from the Cheerleaders. :D
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1829. KEEPEROFTHEGATE (Mod)
POSS T.C.F.A.
97L/INV/XX/XX
MARK
15.85N/60.71W
Member Since: July 15, 2006 Posts: 170 Comments: 53623
Quoting 1812. TropicalAnalystwx13:

Maybe if this was a better developed system. But 97L is a disorganized wave with little reflection higher than 850mb, meaning its track should be dictated by the low-level flow which is predominantly west, if not a little west-southwest. No?


Not according to the last three ATCF fixes, showing it to be mid-level in organization

AL, 97, 2013090112, , BEST, 0, 140N, 590W, 30, 1008, LO, 0, , 0, 0, 0, 0, 1012, 200, 80, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 97, 2013090118, , BEST, 0, 140N, 597W, 30, 1008, LO, 0, , 0, 0, 0, 0, 1012, 200, 70, 0, 0, L, 0, , 0, 0, INVEST, M,
AL, 97, 2013090200, , BEST, 0, 140N, 607W, 30, 1008, LO, 34, NEQ, 0, 0, 0, 0, 1011, 200, 70, 0, 0, L, 0, , 0, 0, INVEST, M,
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Quoting 1818. unknowncomic:
From that it looks like it should go west or wsw.

Yep

D-Max starts in 2 hours and peaks at sunrise it surely going to be interesting
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Quoting 1819. KEEPEROFTHEGATE:
a wave and its waving
LOL
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1825. KEEPEROFTHEGATE (Mod)
the area near yuc should be declared an invest soon
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Quoting 1789. WoodyFL:


Looks like 97L has a rather high potential to be our first hurricane down the line.
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Quoting 1821. WoodyFL:
I know from reading the blog that intensity is the hardest thing to predict but lots of models are showing a strong system. I dont know but it guess it has some peoples attention.

Look at when those models start to ramp it up, not for another 24-36 hours.
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DMIN is really a pest :(
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1821. WoodyFL
I know from reading the blog that intensity is the hardest thing to predict but lots of models are showing a strong system. I dont know but it guess it has some peoples attention.

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It has an expansive moisture field, so dry air will not be an issue or impediment to development, what will be though is the ULL over Hispaniola and the one north of it, we'll see if D-MAX will allow it to re-fire convection.

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1819. KEEPEROFTHEGATE (Mod)
Quoting 1816. HurricaneCamille:


what the heck is that thing
a wave and its waving
Member Since: July 15, 2006 Posts: 170 Comments: 53623
Quoting 1807. wunderkidcayman:
97L should be moving W-WSW soon

From that it looks like it should go west or wsw.
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1817. KEEPEROFTHEGATE (Mod)
Quoting 1811. HurricaneCamille:
i sorry but the fact we tracking something like 97L at this time in hurricane season is kind of pathetic I think.

look so poor right now im cant believe they giving this area so much %.
it surpose to look like this and refire shortly always have convective cycles
just cause you can't see it does not mean its not there
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Quoting 1813. KEEPEROFTHEGATE:
XX/XX/XX


what the heck is that thing
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1815. pcola57


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97L is braking up, yea. With the ULL over the DR not moving the another NE of it the GFS model looks to be on track. It does not develope, I hope.
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1813. KEEPEROFTHEGATE (Mod)
XX/XX/XX
Member Since: July 15, 2006 Posts: 170 Comments: 53623
Quoting 1796. beell:
97L may be getting involved in a mid-level tug-of-war this evening as an inverted 500mb trough passes by to the north. Probably enough to pull the wave axis north towards this weakness or at the least, towards retreating 500 mb heights.

After it dampens out on Tuesday or Wednesday, 97L would be free to continue towards the west but with a resulting track over/near Hispaniola and Cuba. This would agree with the current model consensus.

But we still do not have a system capable of being resolved by any model with any degree of reliability.
So...


09/01 18Z GFS 500 mb Vort-Valid 12Z 09/02

Some northward pull of the mid levels noted along 57W.


(click for full image loop)


Maybe if this was a better developed system. But 97L is a disorganized wave with little reflection higher than 850mb, meaning its track should be dictated by the low-level flow which is predominantly west, if not a little west-southwest. No?
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i sorry but the fact we tracking something like 97L at this time in hurricane season is kind of pathetic I think.

look so poor right now im cant believe they giving this area so much %.
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20130901 2345 14.7 61.7 Too Weak 97L 97L Check out those coordinates.



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sept 2 and

6
bust and bust
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1808. will40
Quoting 1803. WoodyFL:


Almost all of the latest models agree with that. I guess how strong it is will determine where it really goes too.


yes Skye showed a graphic earlier showing how high it is in vertical
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97L should be moving W-WSW soon

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1806. WoodyFL
Quoting 1798. unknowncomic:
That could be a center relocation seeing as it is over the mountains of Hispanola.


yeah it could. i can't find a way to post them but the other 00z models show more of a track not directly over the mountains. its in one of the google earth things and i can't access it to post.
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1805. Droab
There was a post about the levee around the lake. I think currently it is around a foot above average. And I think it was within the last 2 weeks in one of the major south Fl newspapers that the Army corp of Engineer did have 6 areas of concern for substantial failure on the levee. What that meant I don't know, cause for panic or concern ?? Also being not far from the Jupiter Inlet I can only imagine what another dump from the lake will do to Indian River Lagoon and our inlet.
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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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