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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Quoting GeorgiaStormz:


both circles had 10% before.
Is it really likely to become a cat2 before hispaniola?
I never saw that on runs before, but I've missed some stuff.

It has a very favorable environment. It's up to it about how intense it wants to become. Wind shear is low, heat content and sea surface temperatures are high, and trade winds are slow.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
HPC Extended


FINAL...

MADE ONLY COSMETIC CHANGES TO THE UPDATE PACKAGE FOR THE FINAL
ISSUANCE. THE TRACK OF THE TROPICAL LOW FROM THE CARIBBEAN WAS
COORDINATED WITH THE NATIONAL HURRICANE CENTER. THE 12Z/20 MODEL
SOLUTIONS ARE STILL DIVERGENT, WITH RELIANCE ON THE MEAN GUIDANCE
THE SAFEST BET.






Day 7


Member Since: September 23, 2005 Posts: 14 Comments: 11027
GFS is going to Shut up a lot of people here again....All the year with this dilemma and the result we all knows.... hE WINS :P
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Quoting GeorgiaStormz:


both circles had 10% before.
Is it really likely to become a cat2 before hispaniola?
I never saw that on runs before, but I've missed some stuff.
just remember, water temps are 85 degree's down where it sits, should the shear die down this could..explode very quickly, but..we wait and see what happens..we do have days and days to be watching what happens to it
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223 KEEPEROFTHEGATE: [animated satellite photos]

To my eye, 99L already looks like its spinning: ie looks more like a (closed)LOw than a DisturBance.
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Nice Jet streak if it can materialize:



Actually predicted to have moisture this time, since it has plenty of time between it and the previous system, could be a big squall line, or maybe supercells, or just rain, it's too far out to tell if it will materialize anything like this.

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Quoting GraduateStudent2012:



Quite the contrary with quite a few models. Hate to digress, but I must.
I may say that most of the models take this to Cuba.I thought you Receive Isaac in August? or it didn`t affect you?
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Quoting TropicalAnalystwx13:

The '10% shouldn't develop thing' is now 20% Invest 99L. It may or may not develop as wind shear relaxes briefly tomorrow and Monday.

We got a red circle at 2pm EDT.


both circles had 10% before.
Is it really likely to become a cat2 before hispaniola?
I never saw that on runs before, but I've missed some stuff.
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Quoting GraduateStudent2012:



Quite the contrary with quite a few models. Hate to digress, but I must.

Oh, and let me guess...if they weren't pointing at Florida they'd be completely unreliable.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
What happen to Cariboy haven`t see him since Rafael.
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Quoting GTcooliebai:
12z CMC:


that is a little to close for comfort
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Quoting GeorgiaStormz:
When did we get a red circle?
What happened to the 10% shouldnt develop thing?
And its now 99L?
What is the forecast for it?

The '10% shouldn't develop thing' is now 20% Invest 90L. It may or may not develop as wind shear relaxes briefly tomorrow and Monday.

We got a red circle at 2pm EDT.

EDIT: Corrected to change 99L to 90L.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
Quoting GraduateStudent2012:


Because of Sandy, Cody, =)

The chances of the system making it to you are slim, Janiel. Sorry.
Member Since: July 6, 2010 Posts: 113 Comments: 31860
When did we get a red circle?
What happened to the 10% shouldnt develop thing?
And its now 99L?
What is the forecast for it?
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URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE WILMINGTON OH
344 PM EDT SAT OCT 20 2012

INZ073>075-080-KYZ089>099-OHZ046-055-061-062-064- 070-071-077>079-
210345-
/O.CON.KILN.FR.Y.0009.121021T0600Z-121021T1300Z/
RIPLEY-DEARBORN-OHIO-SWITZERLAND-CARROLL-GALLATIN -BOONE-KENTON-
CAMPBELL-OWEN-GRANT-PENDLETON-BRACKEN-ROBERTSON-M ASON-DELAWARE-
FRANKLIN OH-MONTGOMERY-GREENE-PICKAWAY-BUTLER-WARREN-HAMILT ON-
CLERMONT-BROWN-
INCLUDING THE CITIES OF...VERSAILLES...LAWRENCEBURG...
RISING SUN...VEVAY...CARROLLTON...WARSAW...BURLINGTON...
INDEPENDENCE...ALEXANDRIA...OWENTON...WILLIAMSTOW N...FALMOUTH...
BROOKSVILLE...MOUNT OLIVET...MAYSVILLE...DELAWARE...COLUMBUS...
DAYTON...XENIA...CIRCLEVILLE...HAMILTON...LEBANON ...CINCINNATI...
MILFORD...GEORGETOWN
344 PM EDT SAT OCT 20 2012

...FROST ADVISORY REMAINS IN EFFECT FROM 2 AM TO 9 AM EDT
SUNDAY...

* TEMPERATURES...CLEARING SKIES SHOULD ALLOW FOR TEMPERATURES TO
FALL INTO THE MID 30S.

* TIMING...FROST MAY FORM LATE TONIGHT AND CONTINUE INTO SUNDAY
MORNING.

* IMPACTS...SENSITIVE PLANTS LEFT OUTDOORS AND UNPROTECTED MAY
BE DAMAGED.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A FROST ADVISORY MEANS THAT FROST IS LIKELY. SENSITIVE OUTDOOR
PLANTS MAY BE KILLED IF LEFT UNCOVERED.

&&

$$
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Member Since: July 21, 2011 Posts: 83 Comments: 7167
Computers don't lie. When their results are wrong, it's due to GarbageInGarbageOut.
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This afternoon's discussion of indirect effects from 99L in Puerto Rico for most of next week.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
349 PM AST SAT OCT 20 2012


WE WILL CONTINUE TO MONITOR THE EVOLUTION OF THE
AFOREMENTIONED SURFACE LOW PRESSURE SYSTEM FOR NEXT WEEK.
ALTHOUGH THERE ARE STILL TIMING AND TRACK DIFFERENCES...MODELS
GENERALLY KEEP SURFACE LOW ON A TRACK WELL TO OUR WEST THROUGH
NORTH...BUT OPEN THE LOCAL AREA UP TO THE POSSIBILITY OF THE
INFLUX OF VERY DEEP TROPICAL MOISTURE...WITH VEERING WIND FLOW
WITH HEIGHT AND FAVORABLE UPPER LEVEL CONDITIONS...IN COMBINATION
WITH LOCAL EFFECTS...INCLUDING SOUTH TO NORTH OROGRAPHIC LIFTING
ACROSS THE CORDILLERA CENTRAL. THE CURRENTLY INDICATED
DEVELOPMENT AND TRACK OF THIS SYSTEM WOULD YIELD SEVERAL DAYS OF
UNSETTLED WEATHER...POSSIBLY BEGINNING AS EARLY AS LATE TUESDAY
NIGHT OR EARLY WEDNESDAY...AND THEN CONTINUING THROUGH THURSDAY
AND FRIDAY AND POSSIBLY BEYOND. ALTHOUGH IT IS STILL MUCH TOO
EARLY FOR ANY DETAILS...THE "POTENTIAL" REMAINS FOR HEAVY
RAINFALL...FLOODING...LOCALLY SEVERE WEATHER AND INCREASINGLY
HAZARDOUS WINDS AND SEAS AT SOME POINT DURING THE EVENT. STAY
TUNED.
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Quoting 1441114:
THIS WILL STRIKE FLORIDA ! COMPUTERS LIE ! When predicting the weather , for GOD sakes weather people use your heads , not LYING computers . One these years you will be very sorry for using the LYING computers .
Please do not use the Lord's name in vain. Why should we listen to you instead of the computer ?
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Quoting GraduateStudent2012:
^_^.

I am so excited that I can hardly contain myself.

...Why?
Member Since: July 6, 2010 Posts: 113 Comments: 31860
looks like Sandy will be here with us tomorrow.I am thinking 90L will not be named.
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Wind Direction (WDIR): NE ( 50 deg true )
Wind Speed (WSPD): 5.8 kts
Wind Gust (GST): 7.8 kts
Wave Height (WVHT): 1.6 ft
Dominant Wave Period (DPD): 5 sec
Average Period (APD): 4.4 sec
Mean Wave Direction (MWD): SSE ( 156 deg true )
Atmospheric Pressure (PRES): 29.75 in
Pressure Tendency (PTDY): -0.09 in ( Falling Rapidly )
Air Temperature (ATMP): 82.9 %uFFFDF
Water Temperature (WTMP): 86.0 %uFFFDF
Dew Point (DEWP): 73.2 %uFFFDF
Heat Index (HEAT): 88.9 %uFFFDF
Wind Speed at 10 meters (WSPD10M): 5.8 kts
Wind Speed at 20 meters (WSPD20M): 5.8 kts


1007.5 and on the way down in advance of 99L reaching that position ( 15N 75W ).
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Quoting unknowncomic:
BAMD TAKES THIS CLOSE TO FLA.
It is too soon to target anyone yet. Computer models will continue to spread the threat for the next 2 to 3 days. I'm glad I'm not chasing this one.
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Models will shift. will it be left or right?
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Quoting goalexgo:
My hurricane name is Tony Montana

Yea, but that's only fiction, mine is a reality lol
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Quoting cwf1069:
Pressure keep falling down now 1007.3 from 1011.3 at 10 am. No doubt we'll have a Trop. Depr. in the next 24 to 36 hrs. All models going straight to my poor Cuba. 2 hurr. at a time, Sindy and the Castro's. That its call bad luck.
My hurricane name is Tony Montana
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Quoting cwf1069:
Pressure keep falling down now 1007.3 from 1011.3 at 10 am. No doubt we'll have a Trop. Depr. in the next 24 to 36 hrs. All models going straight to my poor Cuba. 2 hurr. at a time, Sindy and the Castro's, that its call bad luck.
Say hello to my little hurricane!
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Quoting GraduateStudent2012:



Am back? You speak as if you know who I am?

At any rate, YES, that we do. Any chance of this being a threat to the Cayman & to Florida down the road?
LOL, we all know who you are.
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Pressure keep falling down now 1007.3 from 1011.3 at 10 am. No doubt we'll have a Trop. Depr. in the next 24 to 36 hrs. All models going straight to my poor Cuba. 2 hurr. at a time, Sindy and the Castro's. That its call bad luck.
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Member Since: July 15, 2006 Posts: 170 Comments: 53456
The BOATS is even more aggressive than the SHIPS...

37 47 64 71 88 101 109
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Quoting KEEPEROFTHEGATE:


yep i call it the slingshot effect
how far forward till the ne recoil is the key


It looks like that trough should be here in two or three days. If it comes down it should move 99L almost directly North or Northeast.
Member Since: July 17, 2009 Posts: 71 Comments: 25961
Quoting MAweatherboy1:

It's sticking with the Nor'Easter theme. Brings it close to the NC coast then it would logically head to the NE from there... this is the last frame:

.

Thanks!
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Looks like way above average precip coming up for the eastern half of the country:



They've also pulled a 180 on that warmup they were showing- now it looks like another big cooldown on the way:



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Quoting Grothar:
Pretty much all the models have 99L going west then a sudden turn North.



yep i call it the slingshot effect
how far forward till the ne recoil is the key
Member Since: July 15, 2006 Posts: 170 Comments: 53456
Member Since: July 17, 2009 Posts: 71 Comments: 25961
Pretty much all the models have 99L going west then a sudden turn North.

Member Since: July 17, 2009 Posts: 71 Comments: 25961

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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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