99L a heavy rainfall threat for Jamaica, Haiti, and Eastern Cuba

By: Dr. Jeff Masters , 2:35 PM GMT on October 21, 2012

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A tropical wave embedded in a large trough of low pressure (Invest 99L) covers a large portion of the Central Caribbean between Hispaniola and the northern coast of South America. This storm has the potential to be a dangerous rainfall threat for Haiti, Jamaica, and eastern Cuba. The disturbance is headed west at less than 5 mph, is over very warm waters of 29°C, and is in a moist environment. 99L has a large area of heavy thunderstorms that have a good degree of spin. These thunderstorms are beginning to organize into spiral bands, as seen on visible satellite loops. However, the amount of heavy thunderstorm activity is about the same as yesterday, and there are no signs of a surface circulation. An Air Force hurricane hunter aircraft is scheduled to investigate 99L this afternoon, but I expect this flight will be rescheduled for later.


Figure 1. Morning satellite image of Invest 99L.

Forecast for 99L
Wind shear is a low 5 - 10 knots, and is forecast to be in the low to moderate range, 5 - 20 knots, through Tuesday. This should allow for some steady development of 99L, and there has been a good deal of model support for 99L becoming a tropical depression by Wednesday. Steering currents favor a continued slow westward movement for 99L through Tuesday. On Wednesday, a strong trough of low pressure to the north of 99L is expected to turn the storm to the north or north-northeast, which should put 99L in the vicinity of Jamaica on Wednesday and Eastern Cuba on Thursday. By Friday, 99L should be in the Central or Eastern Bahamas. It is unclear at this point whether or not the trough pulling 99L to the north will be strong enough to pull the storm all the way out to sea to the northeast; a narrow ridge of high pressure has the potential to build in over 99L late this week and force the storm west-northwest, with a potential threat to the western Bahamas and U.S. East Coast by next weekend. In their 8 am EDT tropical weather outlook, NHC gave 99L a 70% chance of developing into a tropical cyclone by Tuesday morning. 99L will be capable of bringing heavy rains of 5 - 10 inches, with isolated amounts of up to 15 inches in mountainous areas, to Jamaica and Haiti, Monday through Wednesday. Heavy rains will begin on Tuesday in Eastern Cuba, and spread northwards into the Central and Eastern Bahamas by Wednesday.

Invest 90L in the middle Atlantic
A tropical wave (Invest 90L) about 830 miles east-northeast of the northernmost Lesser Antilles Islands is headed west-northwest at about 10 mph. The disturbance has a small amount of heavy thunderstorms, as seen on visible satellite images, and has gotten tangled up with an upper-level low pressure system. This upper-level low is providing 90L the spin it needs to become a tropical cyclone, but is also pumping cool, dry air into the disturbance, which will keep any development slow over the next few days. Wind shear is a moderate 10 - 20 knots, and is forecast to remain in the moderate range until Tuesday. This may allow for some slow development of 90L before it encounters high wind shear of 20 - 30 knots on Tuesday night through Thursday. None of the reliable computer models develop 90L into a tropical cyclone, and it's unlikely that 90L will affect any land areas. In their 8 am EDT tropical weather outlook, NHC gave 90L a 30% chance of developing into a tropical cyclone by Tuesday morning.

The next name on the list of Atlantic tropical storms for 2012 is Sandy.

Jeff Masters

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421. ncstorm
10:41 PM GMT on October 21, 2012
the GFS was showing the splitting of the system in two lows before Cuba and now its showing it around Bermuda..models-smodels..wait and see is all we can do..

GOM, you might be next in the run..
Member Since: August 19, 2006 Posts: 13 Comments: 15997
420. Dakster
10:41 PM GMT on October 21, 2012
What the chances 99L goes *poof*?
Member Since: March 10, 2006 Posts: 0 Comments: 10567
419. TropicalAnalystwx13
10:40 PM GMT on October 21, 2012
The 18z GFS has the same synoptic pattern as the 12z GFS but shows a completely different track. Doesn't make much sense to me.
Member Since: July 6, 2010 Posts: 113 Comments: 32501
418. GeoffreyWPB
10:40 PM GMT on October 21, 2012
Member Since: September 10, 2007 Posts: 0 Comments: 11386
417. wxchaser97
10:39 PM GMT on October 21, 2012
Like I said, the NE still isn't safe this run. They get there own storm of their own, of course it is extra-tropical. Coastal areas are getting rain and inland areas would get some snow, happy Halloween.
252hrs:

Member Since: March 16, 2012 Posts: 127 Comments: 7956
416. washingtonian115
10:36 PM GMT on October 21, 2012
Quoting ncstorm:
and just that quick..the GFS has gone back to the NE scenario again..oh boy
The stick'in Floridians are spared(you all know I love ya'll).I'm favoring a Noel track.
Member Since: August 14, 2010 Posts: 10 Comments: 17472
415. wxchaser97
10:35 PM GMT on October 21, 2012
While 99L doesn't hit or brush the NE another low does come close.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
414. Dakster
10:35 PM GMT on October 21, 2012
I remember someone sayin this earlier, but bears repeating.

Remember tonight to watch for the Meteor shower. Supposed to be the best night to watch.

Member Since: March 10, 2006 Posts: 0 Comments: 10567
413. washingtonian115
10:34 PM GMT on October 21, 2012
Quoting Doppler22:

Yeah/... they worked together on something finally and figured it'd be a good idean to put one there :p
They can't have their dirty secrets up in the air get it?(you know because tornado's suck things into nthe air).
Member Since: August 14, 2010 Posts: 10 Comments: 17472
412. hurricane23
10:34 PM GMT on October 21, 2012
Caribbean has been hostile for entire season.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
411. wxchaser97
10:34 PM GMT on October 21, 2012
Quoting hurricane23:


Its 2012.. might not even develope at all.

Yeah but... I think it will develop. It should have enough time and ingredients to develop and strengthen, plus basically every model develops it.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
410. hurricane23
10:32 PM GMT on October 21, 2012
Quoting TropicalAnalystwx13:

I would..

I think you're getting these are 48 hour percentages...as in from now to Tuesday evening.


Its 2012.. might not even develope at all.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
409. ncstorm
10:31 PM GMT on October 21, 2012
and just that quick..the GFS has gone back to the NE scenario again..oh boy
Member Since: August 19, 2006 Posts: 13 Comments: 15997
408. TropicalAnalystwx13
10:31 PM GMT on October 21, 2012
Quoting hurricane23:
As of now 99L continues to experience 20-25 knots of westerly wind shear. Would not be suprised if percentages are lowered a tad soon.

I would..

I think you're getting these are 48 hour percentages...as in from now to Tuesday evening.
Member Since: July 6, 2010 Posts: 113 Comments: 32501
407. wxchaser97
10:30 PM GMT on October 21, 2012
99L deepens to 966mb but isn't pulled north yet at 180hrs.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
406. hurricane23
10:27 PM GMT on October 21, 2012
As of now 99L continues to experience 20-25 knots of westerly wind shear. Would not be suprised if percentages are lowered a tad soon.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
405. wxchaser97
10:27 PM GMT on October 21, 2012
Quoting Dakster:


When it comes to hurricanes, I will take a glancing blow over a direct hit.

I think a lot of people agree with you on that.


Lol never mind, the image hadn't updated yet...
Member Since: March 16, 2012 Posts: 127 Comments: 7956
404. Abacosurf
10:26 PM GMT on October 21, 2012
Quoting wxchaser97:

Well it does continue and it is moving north at 144hrs. Florida could still get impacts though even if it is a little farther east.
good 100 mile difference. To be expected this far out.

Should help fill a lot of cisterns.
Member Since: August 28, 2008 Posts: 0 Comments: 455
403. Dakster
10:25 PM GMT on October 21, 2012
Quoting wxchaser97:

Well it does continue and it is moving north at 144hrs. Florida could still get impacts though even if it is a little farther east.


When it comes to hurricanes, I will take a glancing blow over a direct hit.
Member Since: March 10, 2006 Posts: 0 Comments: 10567
402. wxchaser97
10:25 PM GMT on October 21, 2012
99L continues off to the NE and strengthen and it had a low come from it and get spat out. 90L is likely going or already extra-tropical at this point and the epac storm exits the image.
162hrs:
Member Since: March 16, 2012 Posts: 127 Comments: 7956
401. wxchaser97
10:20 PM GMT on October 21, 2012
Quoting Dakster:
keep that eastern shift going...

Well it does continue and it is moving north at 144hrs. Florida could still get impacts though even if it is a little farther east.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
Hurricane chaser should head to the Bahamas.
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Quoting washingtonian115:
Well there was very dark clouds and some wind wind the rain was coming in.It's like we have a invisable tornado sheild protecting D.C.Maybe the politicans created it.Lol.

Yeah/... they worked together on something finally and figured it'd be a good idean to put one there :p
Member Since: February 13, 2012 Posts: 11 Comments: 3816
hr 144 final

Member Since: July 15, 2006 Posts: 175 Comments: 54782
Quoting wxchaser97:
12z at 132hrs:


18Z at 132hrs:

90L and the epac storm are stronger this run but this comparison shows the similarities.


12Z run 99L was definately closer to Fl.
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keep that eastern shift going...
Member Since: March 10, 2006 Posts: 0 Comments: 10567
Quoting Doppler22:

There was a tornado by me :o
Well there was very dark clouds and some wind wind the rain was coming in.It's like we have a invisable tornado sheild protecting D.C.Maybe the politicans created it.Lol.
Member Since: August 14, 2010 Posts: 10 Comments: 17472
Quoting GeoffreyWPB:


Taking the current forecasted track, portions of south Florida could be under at least a Tropical Storm Watch/Warning, depending on its size and wind radii.

Gro, have the models been trending differently during the afternoon?


Most are similar to last nights runs. European did come westward though.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
135 hr

Member Since: July 15, 2006 Posts: 175 Comments: 54782
12z at 132hrs:


18Z at 132hrs:

90L and the epac storm are stronger this run but this comparison shows the similarities.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
129 hr

Member Since: July 15, 2006 Posts: 175 Comments: 54782
18z GFS shows a slight shift to the East based on its distance from Fl.
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Quoting Grothar:


Yes, we across "the Pond" still using the old dates and measuring systems. I read about the rains in France, but I didn't realize how bad it was in Spain.

Heres a link to the floods in France, its about the same over the mountains in Northern Spain. Massive damage:-

Pilgrims evacuated as French floods hit Lourdes shrine

http://www.bbc.co.uk/news/world-europe-20019587

Heres a link to what has been happening on the floods front recently. Most of it not on the plain I might add. Some interesting photos, most of them over the last month, links a bit long but I just put floods in Spain, into the google search thing.

http://www.google.co.uk/search?q=spanish+floods&h l=en&safe=off&qscrl=1&rlz=1T4ADRA_enES400ES400&prm d=imvnsu&tbm=isch&tbo=u&source=univ&sa=X&ei=iHKEUL _bDNOLhQeUm4GQDg&sqi=2&ved=0CC8QsAQ&biw=1304&bih=6 05
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Quoting washingtonian115:
Can someone post the other version of the GFS please?.

372.Yeah that rain was pouring like mad.Saw some minimal street flooding.It was insane and it rained almost the whole night moderately.

There was a tornado by me :o
Member Since: February 13, 2012 Posts: 11 Comments: 3816
Quoting Grothar:


I think a lot of rain and a lot of wind. Could be another Isaac type event, but more steady wind and a lot of beach erosion.


Taking the current forecasted track, portions of south Florida could be under at least a Tropical Storm Watch/Warning, depending on its size and wind radii.

Gro, have the models been trending differently during the afternoon?
Member Since: September 10, 2007 Posts: 0 Comments: 11386
Quoting Dakster:


Why not? You could rack up 22,000 posts in a matter of months if you did that.

I thought that was by posting the advisories, this could get me over TA if I post every frame. Anyway... at 120hrs 90L is at 997mb but getting picked up by a trough. 99L is a hurricane and it looks very similar to the 12z run.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
120 hr

Member Since: July 15, 2006 Posts: 175 Comments: 54782
Quoting wxchaser97:

I'm waiting for something interesting to show up so I'm not posting every frame.

90L does strengthen some and 99L does a similar thing as the 12Z run(108hrs).
90L looks to be the next Kirk/Gordon.Looks like Tony/Sandy has it in for the Bahamas.
Member Since: August 14, 2010 Posts: 10 Comments: 17472
Quoting wxchaser97:

I'm waiting for something interesting to show up so I'm not posting every frame.

90L does strengthen some and 99L does a similar thing as the 12Z run(108hrs).


Thank you for not posting every singe frame of every run. Just the interesting ones should do. ;)
Member Since: July 2, 2011 Posts: 0 Comments: 1183
Quoting wxchaser97:

I'm waiting for something interesting to show up so I'm not posting every frame.

90L does strengthen some and 99L does a similar thing as the 12Z run(108hrs).


Why not? You could rack up 22,000 posts in a matter of months if you did that.
Member Since: March 10, 2006 Posts: 0 Comments: 10567
Quoting washingtonian115:
Thanks wxchaser97 can you continue to post the rest of the run.It seems 90L does develop and become Tony/Sandy.

I'm waiting for something interesting to show up so I'm not posting every frame.

90L does strengthen some and 99L does a similar thing as the 12Z run(108hrs).
Member Since: March 16, 2012 Posts: 127 Comments: 7956
hr 111

Member Since: July 15, 2006 Posts: 175 Comments: 54782
hr 102

Member Since: July 15, 2006 Posts: 175 Comments: 54782
hr 96

Member Since: July 15, 2006 Posts: 175 Comments: 54782
Quoting wxchaser97:
At 90hrs 99L is a stronger TS and there is a little something in the open Atlantic.
Thanks wxchaser97 can you continue to post the rest of the run.It seems 90L does develop and become Tony/Sandy.
Member Since: August 14, 2010 Posts: 10 Comments: 17472
hr 90

Member Since: July 15, 2006 Posts: 175 Comments: 54782
At 90hrs 99L is a stronger TS and there is a little something in the open Atlantic.
Member Since: March 16, 2012 Posts: 127 Comments: 7956
hr 84

Member Since: July 15, 2006 Posts: 175 Comments: 54782
Can someone post the other version of the GFS please?.

372.Yeah that rain was pouring like mad.Saw some minimal street flooding.It was insane and it rained almost the whole night moderately.
Member Since: August 14, 2010 Posts: 10 Comments: 17472
Quoting washingtonian115:
Well I kinda knew this was coming as our October has been pretty wet now.The last time we had a October this wet was 2009.It appears the NAO is negative(which I hope it stays through the winter).So it wouldn't be all to surprising if a big storm runs up the coast.

Hey wash.... the other night... i think it was Friday night... Did u get storms bad??
Member Since: February 13, 2012 Posts: 11 Comments: 3816
hr 75

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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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