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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1905. GatorWX
Quoting 1887. KoritheMan:


He's highly ignorant. Ignore him.


Perhaps he is young and was unaware.
Member Since: January 1, 2008 Posts: 0 Comments: 2983
One more try to post the image.

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1903. KEEPEROFTHEGATE (Mod)
1
Member Since: July 15, 2006 Posts: 171 Comments: 53827
GFS flopped big time with 96L not really looking at it until there is a named syatem out there.
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1901. whitewabit (Mod)
Quoting 1892. saltydogoftheseas:


that Sat was put back in service several months ago ..
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not good.

Member Since: August 2, 2011 Posts: 0 Comments: 1923
Quoting 1890. redwagon:


Have you noted any further annular presentation today? Is ASCAT still showing ridiculously symmetrical expansive wind field? How can we expect a productive DMAX when we have two or three centers? How can we take any track models seriously with this schizophrenia? Since when did cyclogenesis support multiple centers so this far away from each other? Boxers or briefs? Ranch or Balsamic? :)


calm down....I did not say it was going to develop....I just pointed out the next 24 maybe even 36 hours will be important for a more northerly pull if development was to occur. If no development then further west it goes!
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Quoting 1894. unknowncomic:
and that looks west or wnw bound.
Ridging developing over top.

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Quoting 1885. hurricanes2018:
its was a tropical low before

Yeah still is but it's open not a closed circulation

Member Since: June 13, 2009 Posts: 2 Comments: 12019
Quoting 1895. wxgeek723:
When did the term "annular" become applicable to undeveloped tropical waves...? Did I miss a Service Change Notice or something? 


Yes. We had one at 3:00 this afternoon.
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When did the term "annular" become applicable to undeveloped tropical waves...? Did I miss a Service Change Notice or something? 
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Quoting 1886. will40:



GFS at 93 hrs
and that looks west or wnw bound.
Member Since: August 2, 2011 Posts: 0 Comments: 1923
1893. Gearsts
Member Since: August 2, 2010 Posts: 0 Comments: 1741
Quoting 1876. saltydogoftheseas:
i have a honest question for all on this blog.....Marilyn formed just like this and with out warning.and can still follow the same path of this storm again if the high pressure ridge fades....computer models are fine when all satellites are functioning but are we not with out one tool the Atlantic satellite in Geo synchronous obit here? if it is fixed i stand corrected.
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Quoting 1888. JLPR2:


Taking longer today but it still has 6hrs to go before the peak of D-max.


This is one instance where I'm hoping dmax doesn't help its chances of cyclogenesis tomorrow.

My storm is coming! :P
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Quoting 1862. TampaSpin:
The next 24 hours are very important with 97L. If it develops into a depression it has a chance to miss the ConUs. If it does not develop the Further West it will move before a recurve. THAT, has a chanace of becoming a very strong system. The longer this thing tracks thru the Caribbean the stronger the system will likely become later.


Have you noted any further annular presentation today? Is ASCAT still showing ridiculously symmetrical expansive wind field? How can we expect a productive DMAX when we have two or three centers? How can we take any track models seriously with this schizophrenia? Since when did cyclogenesis support multiple centers so this far away from each other? Boxers or briefs? Ranch or Balsamic? :)
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Quoting 1879. hurricanes2018:
its going to be a open tropical wave soon.

As far as I know it's been an open wave since 6pm
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1888. JLPR2


Taking longer today but it still has 6hrs to go before the peak of D-max.
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Quoting 1883. Maineweatherguy20023:

isnt that what is is now?


He's highly ignorant. Ignore him.
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1886. will40



GFS at 93 hrs
Member Since: September 19, 2005 Posts: 2 Comments: 4227
Quoting 1883. Maineweatherguy20023:

isnt that what is is now?
its was a tropical low before
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Quoting 1875. RufusBaker:
97l is currently doing what every other system has done so far this year :: FALL APART! the convection is vanishing into nothing now
u are right on the ball tonight u are so right about every storm falling apart
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Quoting hurricanes2018:
its going to be a open tropical wave soon.

isnt that what is is now?
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The GFS now wants to develop the TW behind 97L.

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.
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1880. KEEPEROFTHEGATE (Mod)
Quoting 1867. Relix:
Looking kinda bad right now. Needs convection ASAP.


yeah waiting on a re-fire
Member Since: July 15, 2006 Posts: 171 Comments: 53827
Quoting 1864. KoritheMan:


Don't see this developing in 24 hours.
its going to be a open tropical wave soon.
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Sorry image did not post. Link.

Link
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It has been a much lower than expected season espically with the forcast from many. Thanks. However their are still concerns ahead. I have not put any shutters up so for this year and I usually have my two big areas up by now, I like that. However the season is not over and it looks like we we will have issues coming. Look what will be in the works.

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i have a honest question for all on this blog.....Marilyn formed just like this and with out warning.and can still follow the same path of this storm again if the high pressure ridge fades....computer models are fine when all satellites are functioning but are we not with out one tool the Atlantic satellite in Geo synchronous obit here? if it is fixed i stand corrected.
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97l is currently doing what every other system has done so far this year :: FALL APART! the convection is vanishing into nothing now
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1874. GatorWX
18, it's not going to die, but it won't be a td in the morning.
Member Since: January 1, 2008 Posts: 0 Comments: 2983
Quoting hurricanes2018:
its look like wind shear hitting this invest 97L that way the heavy rain its to the east of the tropical wave and going to have no more rain to it soon.. die out fast

Dont tell that to CaribBoy...
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1872. beell
00Z Soundings. Perhaps some dry air intrusion on northeast winds wrapping in from the west.


Barbados


Guadeloupe


St. Martin


San Juan
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1871. GatorWX
Quoting 1857. KoritheMan:




Dry air from South America may have been an issue.


There was a fairly large pocket sw that appeared quite dense this morning. I'm assuming, since it essentially hasn't moved, it eventually became entrained, it may not recover so quickly.
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its look like wind shear hitting this invest 97L that way the heavy rain its to the east of the tropical wave and going to have no more rain to it soon.. die out fast
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I follow the BAM models a lot at this point. They generally give you a spread of a weak and strong system. This is fairly tightly clustered at the moment.

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Quoting hurricanes2018:
This invest 97L not going to do anthing bad maybe rain and that is..

Yep. BUT rain can be VERY VERY bad. Haiti and lake O are 2 examples in the region...
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1867. Relix
Looking kinda bad right now. Needs convection ASAP.
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Quoting 1859. Maineweatherguy20023:

Im in New England too- I kinda doubt it. Convection died this evening which leads me to believe we'll have s struggling storm traversing the Carib on a westerly heading. So, no. if thats good or bad, that depends on the person.
This invest 97L not going to do anthing bad maybe rain and that is..
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Quoting 1855. GatorWX:


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....



It could be drier air from South America, but it doesn't seem to be impeding development, I'm more inclined to believe westerly wind shear is halting development from the 2 ULL's as well as giving the illusion that the system has slowed down by halting movement of the thunderstorms with the actual DVORAK low level center fix. TPW content seems high enough on the GFS model in that area.
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Quoting 1862. TampaSpin:
The next 24 hours are very important with 97L. If it develops into a depression it has a chance to miss the ConUs. If it does not develop the Further West it will move before a recurve. THAT, has a chanace of becoming a very strong system. The longer this thing tracks thru the Caribbean the stronger the system will likely become later.


Don't see this developing in 24 hours.
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Quoting 1833. beell:


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.




Thanks, Beell, that's the most reasonable, well thought out explanation of what we're seeing other than we all know the system has a large circ and is elongated. Good discernment. Makes sense too. It would fit the idea of competing vortices (hence the elongation) and a continuous competition for convection, I think. It's also serving to maintain instability, but sooner or later something has to give.

I'm thinking that the low coc(s) is not really at the surface still. That would increase symmetrical vorticity which we're not seeing. And, it's trying to wind up in the 700mb and up range instead, but is meeting with difficulty as you described. And, both areas in general are getting vented very well allowing it to sustain its present unorganized state.

The LLC is going to have to do the heavy lifting for it to get going. Has to be at/very near the surface, become dominate, tighten the circ, and as broad as it is now, that will take several hours, it it can pull it off at all. Still, it's a vigorous system, I don't think it's going away. We may see it wane tremendously, much further, before we actually see it crank up as we'd expect.
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The next 24 hours are very important with 97L. If it develops into a depression it has a chance to miss the ConUs. If it does not develop the Further West it will move before a recurve. THAT, has a chanace of becoming a very strong system. The longer this thing tracks thru the Caribbean the stronger the system will likely become later.
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SE convection movement now turned into NE.... If it turns more into the NE, then the track will have to be adjusted when it begins going W

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I am right this time I say invest 97L will die out tonight
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Quoting BrandenCordeiro:
Any chance this effects New England?

Im in New England too- I kinda doubt it. Convection died this evening which leads me to believe we'll have s struggling storm traversing the Carib on a westerly heading. So, no. if thats good or bad, that depends on the person.
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0z GFS at 66 hours:

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Quoting 1855. GatorWX:


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....







Dry air from South America may have been an issue.
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1856. will40
NC if you are on we have some nasty stuff headed our way
Member Since: September 19, 2005 Posts: 2 Comments: 4227
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....



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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.