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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that ULL is moving away a decent clip
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Quoting 47. KEEPEROFTHEGATE:
nice sunday morning update

97 still moving along once it gets pass CaribBoys house should be good to go



Keep, that one got an outloud chuckle. ;) G'morning. The tropical cards seem to be turning as we head into the climo peak, and perhaps not so friendly. 97L may be trouble.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
New wave introduced with low pressure at 45W behind 97L. This one has to be watched.

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Quoting 39. GTstormChaserCaleb:
That ULL centered over DR is in the way.



But pulling away.




Yes ULL is currently over Haiti/D.R. You can see its effect on the convection to the West of 97L (blowing the tops off the convection to the north). It definitely needs to get moving out of the way for 97L to have a chance.
Member Since: September 16, 2007 Posts: 0 Comments: 7311
Quoting 27. IKE:

You might need to go take a walk.


I'm gonna swim instead :)
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47,

lol
Member Since: January 1, 2008 Posts: 0 Comments: 3382
Quoting 36. LargoFl:
might get another one behind 97L end of the week....


Maybe NAM will be the winner with this one Largo. Everyone always writes off that one. I think the UKMET followed suit as well more recently. Hmmmm.
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nice sunday morning update

97 still moving along once it gets pass CaribBoys house should be good to go
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buoy data would suggest this is already a Tropical storm wind wise, now we need to locate the main LLC is there a recon mission I havent looked just got out of bed.
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Quoting 36. LargoFl:
might get another one behind 97L end of the week....


Well... I've just said I would not complain anymore for today XD
Member Since: October 6, 2007 Posts: 0 Comments: 6228
are their any decent bouys near? i see nothing but bouys not reporting....
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Kettle this is the pot calling and guess what you're black......

This year is killing me, any little invest that forms is already a tropical storm or hurricane 3 days later. Every little cloud movement has a new center forming.

Back to lurking and hoping the eastern Caribbean goes back to it's old graveyard self before this thing even thinks of forming.
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97L is fighting with some decent wind shear based on water vapor satellite. Seems like winds are blowing/pushing convection to the north. Hopefully this will back off a bit and let the convection build to the south of the system (which it needs to protect its center).
Member Since: September 16, 2007 Posts: 0 Comments: 7311
Member Since: September 27, 2007 Posts: 1 Comments: 21411
Quoting 26. VR46L:


Man I am starting to pray you get a storm hit soon .. with the way the season is going, you are going to be a crazy cat before long :)


Lol crazy cats are very funny
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That ULL centered over DR is in the way.



But pulling away.

Member Since: June 30, 2013 Posts: 12 Comments: 8422
Thank you Dr M!




This sure is a tricky one! Are looks simply deceiving? Center vorticy sure is looking healthy.
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BAMD thinks charlie we'll have to wait for what the better models think.
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might get another one behind 97L end of the week....
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The 7 day has this system south of Cube ina week..A bit slow perhaps.?
Member Since: September 27, 2007 Posts: 1 Comments: 21411
Quoting Hurricanes305:
Repost: Some very intense convection quickly expanding over 97L; the islands are going to feel some gale force winds and torrential rain even if it does not develop especially since it is moving slowly south of due west. At the moment the strong SW inflow is a credit to why the blob to its east is rapidly increasing. As the easterlies slow down ahead of the LLC and weak steering currents take over air is beginning to piling up as the LLC wraps around the weak easterlies around and force SW inflow to feed convection. As long as it keep this up, upper level winds will quickly fall and a more anticyclonic flow will take over. I believe this will continue through the day and as it crosses the islands tonight it should take off as it stack the cold cloud tops on top of the LLC.

It appears to be forming another COC under the deepest convection, near 15N , 59W...
Member Since: May 31, 2011 Posts: 0 Comments: 912
Quoting 24. wunderkidcayman:

Dude quit it I'm getting really sick hearin you complain about this look this system will bring you some good rain take it or leave it just stop complaining please I beg of you


Okay I'll stop complaining for today XD...
Member Since: October 6, 2007 Posts: 0 Comments: 6228
Quoting 15. CaribBoy:
I'm bored with that south of due west movement... while every time these things want to go more north than south. WHY THE HECK THIS DID NOT HAPPEN WHEN DORIANS REMAINS WHERE JUST NORTH OF US!!


Ok look I know how you feel I feel the same way when it dry as the Sahara here and trust me I know but when you get rain and showers just be greatfull
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yea...watch wind speed and direction.....was west, then southwest and actually started turn southerly ...but the last few updates have tried to bend back from the west/sw...and pressure which has leveled out ...i think a coc is trying to get better defined to the NNE of the island, directly west of Martinique...


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Surface convergence is back, but stretched out.

Member Since: June 30, 2013 Posts: 12 Comments: 8422
looks to me moving west dont let the convection fool you
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27. IKE

Quoting CaribBoy:
I'm bored with that south of due west movement... while every time these things want to go more north than south. WHY THE HECK THIS DID NOT HAPPEN WHEN DORIANS REMAINS WHERE JUST NORTH OF US!!
You might need to go take a walk.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting 19. CaribBoy:


Angry!!


Man I am starting to pray you get a storm hit soon .. with the way the season is going, you are going to be a crazy cat before long :)
Member Since: March 1, 2012 Posts: 0 Comments: 6927
Member Since: April 24, 2011 Posts: 1 Comments: 601
Quoting 15. CaribBoy:
I'm bored with that south of due west movement... while every time these things want to go more north than south. WHY THE HECK THIS DID NOT HAPPEN WHEN DORIANS REMAINS WHERE JUST NORTH OF US!!

Dude quit it I'm getting really sick hearin you complain about this look this system will bring you some good rain take it or leave it just stop complaining please I beg of you
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23. SLU
Since the circulation is elongated, reformations will be common until it finally focusses the energy in one location.

Looks like the 12z center has dissipated with a new one forming near 15n 59w, give or take a few miles.

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Good Blog doc!
I think that when this gets to the western Caribbean, we may have a problem on our hands..
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evere one in the gulf of mx needs too keep a vary close eye on 97L
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Angry!!
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Thanks Doc.
Member Since: September 27, 2007 Posts: 1 Comments: 21411
Quoting 15. CaribBoy:
I'm bored with that south of due west movement... while every time these things want to go more north than south. WHY THE HECK THIS DID NOT HAPPEN WHEN DORIANS REMAINS WHERE JUST NORTH OF US!!


As Bubba says " I feel your pain CaribBoy "
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Quoting 13. LargoFl:


Something is happening here.....What it is ain't exactly clear...............
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I'm bored with that south of due west movement... while every time these things want to go more north than south. WHY THE HECK THIS DID NOT HAPPEN WHEN DORIANS REMAINS WHERE JUST NORTH OF US!!
Member Since: October 6, 2007 Posts: 0 Comments: 6228
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

Thanks Doc ! For that infomation !
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Thanks Doc
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Thank you Dr Masters! Good Morning Class! Everyone starting to get a twitch in their britches?
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Looking at satellite loops, one can see cumulus clouds streaking into 97L from the SW to the NE. This is indication that something is going on around the surface. Several surface observations from the islands are showing west or WSW winds and pressures are dropping. This leads me to believe 97L is either close to having a closed circulation or already has one. The NHC seems to agree with this in their latest TWO.
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Good blog, Doc. Agreed. Thanks.

Except, I'm thinking the JHR, and the trade winds mentioned, will have less of an effect on 97L providing it can consolidate its circulation and produce continuous convection overhead and to its southwest.
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Thanks Doc 1
Member Since: March 1, 2012 Posts: 0 Comments: 6927
Repost: Some very intense convection quickly expanding over 97L; the islands are going to feel some gale force winds and torrential rain even if it does not develop especially since it is moving slowly south of due west. At the moment the strong SW inflow is a credit to why the blob to its east is rapidly increasing. As the easterlies slow down ahead of the LLC and weak steering currents take over air is beginning to piling up as the LLC wraps around the weak easterlies around and force SW inflow to feed convection. As long as it keep this up, upper level winds will quickly fall and a more anticyclonic flow will take over. I believe this will continue through the day and as it crosses the islands tonight it should take off as it stack the cold cloud tops on top of the LLC.

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Still no Atlantic storms in the making... This could be a very slow season indeed. Despite me thinking it would not be.
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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.