Caribbean disturbance 99L a dangerous rainfall threat for Haiti, Jamaica, and Cuba

By: Dr. Jeff Masters , 4:12 PM GMT on October 20, 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 are beginning to show some organization, as seen on visible satellite loops. 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, which will bring a multi-day period of heavy rains to Haiti, Jamaica, and eastern Cuba beginning on Sunday. The Dominican Republic may also see some heavy rains, though not as great. On Wednesday, a strong trough of low pressure will approaching the Eastern U.S., and the GFS and ECMWF models predict that this trough will turn 99L to the north, bringing the storm into the southeast Bahama Islands on Thursday or Friday. In their 8 am EDT tropical weather outlook, NHC gave 99L a 30% chance of developing into a tropical cyclone by Monday morning. I put these odds higher, at 40%. An Air Force hurricane hunter aircraft is scheduled to investigate 99L on Sunday afternoon.


Figure 1. Morning satellite image of Invest 99L.

Invest 90L in the middle Atlantic
A tropical wave (Invest 90L) about 1000 miles east-northeast of the northernmost Lesser Antilles Islands is headed west-northwest at about 10 mph. The disturbance has a modest 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 pumping cool, dry air into the disturbance, which will keep any development slow over the next few days. Wind shear is a high 20 - 25 knots, but is forecast to drop to the moderate range, 10 - 20 knots, Sunday through Monday. This may allow for some slow development of 90L before it encounters very high wind shear of 20 - 40 knots on Tuesday and Wednesday. None of the reliable computer models develop 90L into a tropical cyclone. It's unlikely that 90L will affect any land areas. In their 8 am EDT tropical weather outlook, NHC gave 90L a 20% chance of developing into a tropical cyclone by Monday morning.

Jeff Masters

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and something else just happened...

6.6 Mwp - VANUATU

Preliminary Earthquake Report
Magnitude 6.6 Mwp
Date-Time
20 Oct 2012 23:00:32 UTC
21 Oct 2012 10:00:32 near epicenter
20 Oct 2012 18:00:32 standard time in your timezone
Location 13.572S 166.594E
Member Since: April 23, 2011 Posts: 104 Comments: 14869
Quoting trHUrrIXC5MMX:
no word why does ATCF gave an update at 15 UTC on Rafael?

I think they are just doing due diligence in tracking the remnants of Rafael...don't they always track a tropical system until its bitter end?
Member Since: September 15, 2009 Posts: 391 Comments: 3519
Quoting washingtonian115:
Not that much and sst have cooled in the gulf as well so don't expect a cat 3 or 4 coming for you.They would have to move at a pretty good clip.


wow...thats a little too high
But I'll enjoy watching it
Member Since: April 23, 2011 Posts: 104 Comments: 14869
501. NCHurricane2009
11:27 PM GMT on October 20, 2012
Quoting Slamguitar:
OFFICIAL SLAMGUITAR TROPICAL WEATHER OUTLOOK "OUTLOOK"

8pm:

99L: 70%
90L: 20%


OFFICIAL NCH2009 OUTLOOK ON SLAMGUITAR TROPICAL WEATHER OUTLOOK OUTLOOK

80% chance of being correct...
Member Since: September 15, 2009 Posts: 391 Comments: 3519
500. trHUrrIXC5MMX
11:27 PM GMT on October 20, 2012
no word why does ATCF gave an update at 15 UTC on Rafael?
Member Since: April 23, 2011 Posts: 104 Comments: 14869
499. MAweatherboy1
11:26 PM GMT on October 20, 2012
Quoting Tropicsweatherpr:
What will 90L be at 8 PM.

A-30%
B-40%
C-50%
D-60%
E-Higher
F-Lower than 30%

I say A.

The NHC will probably do 30%, but I think it should be higher. I really wouldn't be surprised at all if we see 90L become a hurricane eventually. It strikes me as a situation very similar to Michael. Chances are it'll either end up being nothing or something pretty big.
Member Since: February 11, 2012 Posts: 79 Comments: 7306
498. KoritheMan
11:26 PM GMT on October 20, 2012
Quoting opal92nwf:
Does anyone think that the Gulf is even a player for this Caribbean System?


With such a deep trough (how many times have we heard that one?) emerging from the Great Lakes a week or so from now, I doubt it.
Member Since: March 7, 2007 Posts: 521 Comments: 19146
497. washingtonian115
11:25 PM GMT on October 20, 2012
Quoting opal92nwf:
Does anyone think that the Gulf is even a player for this Caribbean System?
Not that much and sst have cooled in the gulf as well so don't expect a cat 3 or 4 coming for you.They would have to move at a pretty good clip.
Member Since: August 14, 2010 Posts: 10 Comments: 15738
496. Tropicsweatherpr
11:25 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D
Quoting



I say B.
Member Since: April 29, 2009 Posts: 75 Comments: 13341
495. Civicane49
11:25 PM GMT on October 20, 2012
Member Since: July 21, 2011 Posts: 82 Comments: 7056
494. Civicane49
11:24 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D


C.

Quoting Tropicsweatherpr:
What will 90L be at 8 PM.

A-30%
B-40%
C-50%
D-60%
E-Higher
F-Lower than 30%

I say A.


A.
Member Since: July 21, 2011 Posts: 82 Comments: 7056
493. KoritheMan
11:23 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D


B
Member Since: March 7, 2007 Posts: 521 Comments: 19146
492. Slamguitar
11:23 PM GMT on October 20, 2012
OFFICIAL SLAMGUITAR TROPICAL WEATHER OUTLOOK "OUTLOOK"

8pm:

99L: 70%
90L: 20%
Member Since: July 2, 2011 Posts: 0 Comments: 1176
491. TropicalAnalystwx13
11:23 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D

C.

Quoting Tropicsweatherpr:
What will 90L be at 8 PM.

A-30%
B-40%
C-50%
D-60%
E-Higher
F-Lower than 30%

I say A.

A.
Member Since: July 6, 2010 Posts: 109 Comments: 30310
490. opal92nwf
11:22 PM GMT on October 20, 2012
Does anyone think that the Gulf is even a player for this Caribbean System?
Member Since: May 12, 2012 Posts: 10 Comments: 1924
489. Tropicsweatherpr
11:22 PM GMT on October 20, 2012
What will 90L be at 8 PM.

A-30%
B-40%
C-50%
D-60%
E-Higher
F-Lower than 30%

I say A.
Member Since: April 29, 2009 Posts: 75 Comments: 13341
488. sunlinepr
11:22 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D


They will keep it 60% though it is organizing...

Member Since: August 2, 2010 Posts: 21 Comments: 9656
487. washingtonian115
11:21 PM GMT on October 20, 2012
Quoting goosegirl1:
It was a glorious day in the Mid Atlantic today. I took a few shots and posted them to my very first blog- let me know if it worked, will you? I just wanted to share the spectacular color before peak has passed.
Did that heavy rain event move over your area as well yesterday?.It was raining cats and dogs for a few minutes and then it went to moderate rain.
Member Since: August 14, 2010 Posts: 10 Comments: 15738
486. Slamguitar
11:21 PM GMT on October 20, 2012
Quoting NCHurricane2009:

Me too! Ever since I moved here...seems like luck is turning up for Michigan sports...


*Patiently waits for Red Wings to play*

*Dies of old age*
Member Since: July 2, 2011 Posts: 0 Comments: 1176
485. MAweatherboy1
11:19 PM GMT on October 20, 2012
Quoting SFLWeatherman:
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D

I say B, with a possibility of C.
Member Since: February 11, 2012 Posts: 79 Comments: 7306
484. wxchaser97
11:19 PM GMT on October 20, 2012
Quoting TropicalAnalystwx13:

But we know the reason of why storms have struggled down there this year and 99L does not have to deal with any of it. Trade winds were an issue for both Ernesto and Isaac, but are significantly slower for 99L.

Wind shear and forward speed are also lower than with Ernesto and Isaac. When you add in high TCHP and SST values you have the ingredients for a tropical cyclone to develop and strengthen.
Member Since: March 16, 2012 Posts: 123 Comments: 7893
483. SFLWeatherman
11:18 PM GMT on October 20, 2012
What will 99L be at 8PM
A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

I say C or D
Member Since: May 23, 2012 Posts: 0 Comments: 4208
482. goosegirl1
11:18 PM GMT on October 20, 2012
It was a glorious day in the Mid Atlantic today. I took a few shots and posted them to my very first blog- let me know if it worked, will you? I just wanted to share the spectacular color before peak has passed.
Member Since: December 17, 2009 Posts: 0 Comments: 1189
481. NCHurricane2009
11:18 PM GMT on October 20, 2012
Quoting wxchaser97:

Hey Michigan won so all is good, at least for me.

Me too! Ever since I moved here...seems like luck is turning up for Michigan sports...
Member Since: September 15, 2009 Posts: 391 Comments: 3519
480. Slamguitar
11:18 PM GMT on October 20, 2012
Quoting wxchaser97:

Hey Michigan won so all is good, at least for me.


Yup, they were the consolation prize for me. WMU and CMU just didn't want to play football today... >_>
Member Since: July 2, 2011 Posts: 0 Comments: 1176
478. sunlinepr
11:18 PM GMT on October 20, 2012
Member Since: August 2, 2010 Posts: 21 Comments: 9656
477. stormpetrol
11:18 PM GMT on October 20, 2012
Not as much convection for 99L, but improved structure and organization is what counts.
Member Since: April 29, 2007 Posts: 0 Comments: 7506
476. KoritheMan
11:17 PM GMT on October 20, 2012
Quoting MAweatherboy1:

We've seen systems struggle time and time again in the Caribbean this year.
That's not a very scientific line of thought. "They struggled before, so they'll struggle now"? Caribbean climatology is important, but the general trade wind rule seems less pragmatic this late into the year. If you want a previous citation, try Tomas. The trade winds typically slacken in October due to a weaker pressure gradient as troughs start becoming more frequent and the western periphery of the ridge erodes. Conditions are different for each system, and we shouldn't just ignore an organizing system because conditions have been climatologically unfavorable (consistent with El Nino earlier in the year) at earlier points in the year.
Member Since: March 7, 2007 Posts: 521 Comments: 19146
475. MAweatherboy1
11:17 PM GMT on October 20, 2012
Looks like some heavy afternoon/evening storms popping up over Jamaica:

Member Since: February 11, 2012 Posts: 79 Comments: 7306
474. NCHurricane2009
11:17 PM GMT on October 20, 2012
Quoting KoritheMan:


Ah yes.

About your Gulf of Guinea comment...my understanding is that as the cool waters in the Gulf contrast with the warm air over Africa...this creates the mid-level African Easterly Jet. The stronger the contrast...the stronger the jet. I guess that jet somehow has troughs and ridges much like how the jet streams toward the poles of the Earth have troughs and ridges...though I never understood exactly how any jet goes "unstable" into troughs and ridges...

I imagine the mid-level AEJ trough creates upper divergence that in turn creates a surface tropical wave....much like how a polar jet stream upper trough creates a surface frontal non-tropical cyclone....
Member Since: September 15, 2009 Posts: 391 Comments: 3519
473. beell
11:17 PM GMT on October 20, 2012
Quoting trHUrrIXC5MMX:


They should have done 40 or 50% at 2 PM to do 60 % at 8pm...


Yes, for sure. Selecting the correct probability is critical to the development of any tropical system. It can make or break the whole deal.
(j/k)
Member Since: September 11, 2007 Posts: 137 Comments: 15358
472. trHUrrIXC5MMX
11:16 PM GMT on October 20, 2012
Who remembers this TD 9 in the Epac in 2009. Back then they didn't have the numeric 10, 30 or 70% values..so they went from low chance to a high chance and TD 9 3 hours later..

who remembers that?
Member Since: April 23, 2011 Posts: 104 Comments: 14869
471. wxchaser97
11:16 PM GMT on October 20, 2012
Quoting Slamguitar:
Well, that was hard. I had to split my attention between three college football games that started at the same time (Alma mater, current college, and future grad school) and our code red in the Carib, and only 1/3 of my teams won!

*Sigh*

Now I can get back to all wx. :)

Hey Michigan won so all is good, at least for me.
Member Since: March 16, 2012 Posts: 123 Comments: 7893
470. stormpetrol
11:15 PM GMT on October 20, 2012
99L should be up to 80% at 8 pm est.
Member Since: April 29, 2007 Posts: 0 Comments: 7506
468. TropicalAnalystwx13
11:14 PM GMT on October 20, 2012
Quoting MAweatherboy1:

I actually agree with you here. I think it's highly unlikely they go down at 8PM, 60% seems like a good bet, but I think they should've only gone to 50% at 2PM. We've seen systems struggle time and time again in the Caribbean this year. Developing systems like this can be slowed or completely derailed by things that we often can't even see. It's better for the NHC to play it a little conservative.

But we know the reason of why storms have struggled down there this year and 99L does not have to deal with any of it. Trade winds were an issue for both Ernesto and Isaac, but are significantly slower for 99L.
Member Since: July 6, 2010 Posts: 109 Comments: 30310
467. Slamguitar
11:13 PM GMT on October 20, 2012
Well, that was hard. I had to split my attention between three college football games that started at the same time (Alma mater, current college, and future grad school) and our code red in the Carib, and only 1/3 of my teams won!

*Sigh*

Now I can get back to all wx. :)
Member Since: July 2, 2011 Posts: 0 Comments: 1176
466. Dakster
11:13 PM GMT on October 20, 2012
Quoting LargoFl:
north of Tampa bay,down in the 40's..............


Quit bragging. 90f today here.
Member Since: March 10, 2006 Posts: 0 Comments: 9768
465. trHUrrIXC5MMX
11:12 PM GMT on October 20, 2012
Quoting KoritheMan:


No they're not. Not in one TWO. Anyone who has followed the National Hurricane Center for any reasonable amount of time knows that any changes on their part will be subtle, and come in periodic increments. They're not just gonna jump from 60% to 50 or 40% based on the diurnal minimum.


They should have done 40 or 50% at 2 PM to do 60 % at 8pm...
Member Since: April 23, 2011 Posts: 104 Comments: 14869
464. KoritheMan
11:12 PM GMT on October 20, 2012
Quoting NCHurricane2009:

In the context of tropical wave formation over Africa...you are right. I was talking about how once they get off the coast of Africa and journey their way across the Atlantic...something like an upper ridge is necessary to ventilate them to get them spinning into tropical cyclones...

99-L case in point...a t-wave who has blown up while sliding under an upper ridge...


Ah yes.
Member Since: March 7, 2007 Posts: 521 Comments: 19146
463. Dakster
11:11 PM GMT on October 20, 2012
Coño. I gotta get the shutters. I thought the season was over....
Member Since: March 10, 2006 Posts: 0 Comments: 9768
462. trHUrrIXC5MMX
11:11 PM GMT on October 20, 2012
Quoting wxchaser97:

I think they may even go up with 99L and 90L, jmo.


yeah 90L is going up.
Member Since: April 23, 2011 Posts: 104 Comments: 14869
461. LargoFl
11:10 PM GMT on October 20, 2012
north of Tampa bay,down in the 40's..............
Member Since: August 6, 2011 Posts: 4 Comments: 33491
460. MAweatherboy1
11:10 PM GMT on October 20, 2012
Quoting trHUrrIXC5MMX:


I have a feeling they might. And I think they went a little too high from 30 to 60% earlier today.

I actually agree with you here. I think it's highly unlikely they go down at 8PM, 60% seems like a good bet, but I think they should've only gone to 50% at 2PM. We've seen systems struggle time and time again in the Caribbean this year. Developing systems like this can be slowed or completely derailed by things that we often can't even see. It's better for the NHC to play it a little conservative.
Member Since: February 11, 2012 Posts: 79 Comments: 7306
459. trHUrrIXC5MMX
11:10 PM GMT on October 20, 2012
In other news...the California Sierra Nevada is going to get the first dump of the white stuff there...

...FIRST SIGNIFICANT SNOWFALL OF THE SEASON FOR THE MOUNTAINS...

.A COLD AND FAIRLY STRONG STORM SYSTEM...BY OCTOBER
STANDARDS...WILL MOVE INTO NORTHERN CALIFORNIA LATE SUNDAY THROUGH
MONDAY. THIS STORM WILL PRODUCE THE FIRST SIGNIFICANT SNOWFALL OF
THE SEASON FOR THE MOUNTAINS.
318 PM PDT SAT OCT 20 2012

...WINTER WEATHER ADVISORY IN EFFECT FROM 11 PM SUNDAY TO 11 PM
PDT MONDAY ABOVE 4000 FEET...
...WINTER STORM WATCH IN EFFECT FROM SUNDAY EVENING THROUGH
MONDAY EVENING ABOVE 5500 FEET...

THE NATIONAL WEATHER SERVICE IN MEDFORD HAS ISSUED A WINTER
WEATHER ADVISORY ABOVE 4000 FEET FOR SNOW...WHICH IS IN EFFECT
FROM 11 PM SUNDAY TO 11 PM PDT MONDAY. A WINTER STORM WATCH ABOVE
5500 FEET HAS ALSO BEEN ISSUED. THIS WINTER STORM WATCH ABOVE 5500
FEET IS IN EFFECT FROM SUNDAY EVENING THROUGH MONDAY EVENING.

* SNOW ACCUMULATIONS...SNOW ACCUMULATIONS OF 8 TO 14 INCHES ARE
EXPECTED ABOVE 5500 FEET. SNOW ACCUMULATIONS BETWEEN OF 4 TO 8
INCHES ARE EXPECTED BETWEEN 4000 AND 5500 FEET. BELOW 4000
FEET...TO INCLUDE MOUNT SHASTA CITY...UP TO 2 TO 4 INCHES OF
SNOW IS POSSIBLE.
Member Since: April 23, 2011 Posts: 104 Comments: 14869
458. Tropicsweatherpr
11:10 PM GMT on October 20, 2012
Quoting stormchaser19:
850mb Vorticity
9 Hours Previous

Now


There are two red x my friend.
Member Since: April 29, 2009 Posts: 75 Comments: 13341
457. KoritheMan
11:10 PM GMT on October 20, 2012
Quoting trHUrrIXC5MMX:


I have a feeling they might. And I think they went a little too high from 30 to 60% earlier today.


No they're not. Not in one TWO. Anyone who has followed the National Hurricane Center for any reasonable amount of time knows that any changes on their part will be subtle, and come in periodic increments. They're not just gonna jump from 60% to 50 or 40% based on the diurnal minimum.
Member Since: March 7, 2007 Posts: 521 Comments: 19146
456. NCHurricane2009
11:09 PM GMT on October 20, 2012
Quoting KoritheMan:


The catalyst for a tropical wave is the temperature difference between Sahel Africa and the Gulf of Guinea.

In the context of tropical wave formation over Africa...you are right. I was talking about how once they get off the coast of Africa and journey their way across the Atlantic...something like an upper ridge is necessary to ventilate them to get them spinning into tropical cyclones...

99-L case in point...a t-wave who has blown up while sliding under an upper ridge...
Member Since: September 15, 2009 Posts: 391 Comments: 3519
455. TropicalAnalystwx13
11:09 PM GMT on October 20, 2012
Quoting KoritheMan:


They're not gonna go down on 99L...

Agreed. If anything, they should go up. Convection has diminished, but only because of DMIN. Its overall structure is much better defined than earlier and it also appears that the associated surface low has consolidated since earlier.

70% or 80% at 8pm EDT for 99L.

Maybe 30% for 90L.
Member Since: July 6, 2010 Posts: 109 Comments: 30310
454. wxchaser97
11:09 PM GMT on October 20, 2012
Quoting trHUrrIXC5MMX:
For 8 PM TWO
I say

99L 50-60%
90L 30%

I think they may even go up with 99L and 90L, jmo.
Member Since: March 16, 2012 Posts: 123 Comments: 7893

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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.