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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Member Since: July 15, 2006 Posts: 173 Comments: 54347
Quoting NCHurricane2009:

Recon is investigating 90L or 99L?

99L, I corrected my post.
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Quoting NCHurricane2009:

Recon is investigating 90L or 99L?


99L.
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Quoting TropicalAnalystwx13:

DMAX in a few hours should cause convection to increase. 90L seems to have a closed circulation, and recon is investigating tomorrow afternoon, so I wouldn't be surprised if this was declared a TD or TS at 5pm EDT.

Recon is investigating 90L or 99L?
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.
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Quoting Civicane49:


Yep. 99L has a well-organized structure but lacks deep convection.

DMAX in a few hours should cause convection to increase. 99L seems to have a closed circulation, and recon is investigating tomorrow afternoon, so I wouldn't be surprised if this was declared a TD or TS at 5pm EDT.
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event detected on going

Member Since: July 15, 2006 Posts: 173 Comments: 54347
Quoting Civicane49:


Yep. 99L has a well-organized structure but lacks deep convection.

99L...the invisi-swirl...
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Quoting TropicalAnalystwx13:
Awesome structure, not so awesome convection.



Yep. 99L has a well-organized structure but lacks deep convection.
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90L:

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Awesome structure, not so awesome convection.

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Speaking of subtropical cyclones...is the Atlantic most prolific in this type of hybrid system?
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poss event detected
Member Since: July 15, 2006 Posts: 173 Comments: 54347
Quoting AussieStorm:

Did he have one in the 1st place, can't lose what you don't have. LOL

Ouch...your humor hits like a dagger...
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Quoting CybrTeddy:
Back on a serious note, 99L is doing fair in structure, but it is doing terrible in convection. This doesn't come as much of a surprise, as we saw the convergence was bare minimal going into DMAX. Developing systems almost always go through the stage were convection is just pathetic looking the day they're declared invests, and the next day. This is going to be a very gradual development, incremental. But it will probably become Tropical Storm Sandy (or Tony, depending on 90L)


90L is starting to resemble a sub-tropical system instead of a tropical one. This is thanks to the ULL you can see itself occluding with.

I agree 90L is more subtropical than tropical...
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Back on a serious note, 99L is doing fair in structure, but it is doing terrible in convection. This doesn't come as much of a surprise, as we saw the convergence was bare minimal going into DMAX. Developing systems almost always go through the stage were convection is just pathetic looking the day they're declared invests, and the next day. This is going to be a very gradual development, incremental. But it will probably become Tropical Storm Sandy (or Tony, depending on 90L)


90L is starting to resemble a sub-tropical system instead of a tropical one. This is thanks to the ULL you can see itself occluding with.
Member Since: July 8, 2005 Posts: 259 Comments: 24169
Phew.

Tropical Cyclone Report: Tropical Storm Aletta (EP012012)

Doing all East Pacific storms first as the season there is *considers biting tongue* probably near its end.
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they are showing up on the big globe as well

Member Since: July 15, 2006 Posts: 173 Comments: 54347
Quoting AussieStorm:
Quoting KEEPEROFTHEGATE:


Just got this one in my email.

== PRELIMINARY EARTHQUAKE REPORT ==
Region: ICELAND REGIONGeographic coordinates: 66.329N, 18.751W
Magnitude: 5.6 Mwp
Depth: 10 km
Universal Time (UTC): 21 Oct 2012 01:25:23
Time near the Epicenter: 21 Oct 2012 01:25:23
Local standard time in your area: 21 Oct 2012 01:25:23
Location with respect to nearby cities:

78 km (49 miles) NNW (337 degrees) of Akureyri, Iceland

201 km (125 miles) E (82 degrees) of Isafjordur, Iceland

264 km (164 miles) WNW (302 degrees) of Neskaupstadur, Iceland 285 km (177 miles) NNE (30 degrees) of REYKJAVIK, Iceland

Does Mwp mean Multi wave pulse?
not sure what it means but somethings going on thats fer sure
Member Since: July 15, 2006 Posts: 173 Comments: 54347
Right now...99-L is probably listening to this tune...specifically the beat from 0:00 to 1:43

But once DMAX picks up...the beat is going to be more like from 1:43 and onwards...
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00z Surface Analysis.

Member Since: April 29, 2009 Posts: 75 Comments: 14315
Quoting wxchaser97:

Me too.


I forecast a system in that intensity range.

80 Mph Category 1 landfall is a reasonable forecast.
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Quoting HurricaneDean07:

Including me.

Me too, I have found out there are more teens on here than I thought there would be.

Quoting HurricaneDean07:

All In agreement of a High-End Tropical Storm, or a category 1 hurricane.

I forecast a system in that intensity range.
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Quoting TropicalAnalystwx13:

You've definitely lost your mind.

Did he have one in the 1st place, can't lose what you don't have. LOL
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Quoting wxchaser97:

He isn't the only teenager here, I know what you mean by what some teens do.

Lol, they are probably.

Including me.
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Quoting Slamguitar:


Too much to do. Essays, midterms, research, job, cleaning my place, things to fix. Add that with being an insomniac and you get no sleep, but I should be able to squeeze in a few hours tonight.

Hang in their...I was like that a year and a half ago...but it pays off in the end....
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Quoting KoritheMan:

I went to work with an hour and a half of sleep yesterday. Have to wake up at 9:30 tomorrow. Not sure how much sleep I'll have, but oh well.


Eh, we're young. We can do it. ;)
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Quoting Slamguitar:


Too much to do. Essays, midterms, research, job, cleaning my place, things to fix. Add that with being an insomniac and you get no sleep, but I should be able to squeeze in a few hours tonight.
I went to work with an hour and a half of sleep yesterday. Have to wake up at 9:30 tomorrow. Not sure how much sleep I'll have, but oh well.
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Quoting NCHurricane2009:

Why y'all not sleepin'? I got plenty last night...but I was exhausted from work last week...


Too much to do. Essays, midterms, research, job, cleaning my place, things to fix. Add that with being an insomniac and you get no sleep, but I should be able to squeeze in a few hours tonight.
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Quoting NCHurricane2009:

Can I get a what what? Oh yeaahhhhhh! Some of y'all think I lost my mind...but we just getting started tonight!

You've definitely lost your mind.
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Quoting Grothar:
More models agreeing on intensity potential.


All In agreement of a High-End Tropical Storm, or a category 1 hurricane.
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Quoting Grothar:


OK, what type of accent do I have then?


I hate arriving to the party late, but is this your accent?

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Quoting HurricaneDean07:

Popcorn convection is now beginning to show up, it will have full convection again in about 3 hours.

Can I get a what what? Oh yeaahhhhhh! Some of y'all think I lost my mind...but we just getting started tonight!
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Quoting HurricaneDean07:
99L has a closed circulation now, all that is needed is convection, which will happen during DMAX...

My Proof
Disable the first 7 frames of the Loop, by clicking on them, and then speed up the loop to full speed. Obvious closed circulation.

It has a great cloud pattern and circulation when you look at that. It does look to be closed and the next ASCAT pass will confirm or bust that. I see convection slowly firing and it is possible that 99L becomes a TD before 24hrs.
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Quoting KEEPEROFTHEGATE:


Just got this one in my email.

== PRELIMINARY EARTHQUAKE REPORT ==
Region: ICELAND REGIONGeographic coordinates: 66.329N, 18.751W
Magnitude: 5.6 Mwp
Depth: 10 km
Universal Time (UTC): 21 Oct 2012 01:25:23
Time near the Epicenter: 21 Oct 2012 01:25:23
Local standard time in your area: 21 Oct 2012 01:25:23
Location with respect to nearby cities:

78 km (49 miles) NNW (337 degrees) of Akureyri, Iceland

201 km (125 miles) E (82 degrees) of Isafjordur, Iceland

264 km (164 miles) WNW (302 degrees) of Neskaupstadur, Iceland 285 km (177 miles) NNE (30 degrees) of REYKJAVIK, Iceland

Does Mwp mean Multi wave pulse?
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Quoting NCHurricane2009:
99-L has even less t-storms...but its surface low is getting even better defined still (near 72.5W-15N)...

Popcorn convection is now beginning to show up, it will have full convection again in about 3 hours.
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Quoting Slamguitar:


I literally got no sleep last night, so I'm glad these are relatively coherent sentences.

You do have a point though. Significant convection will start to take place at Dmax and will have to persist at least into the afternoon/evening. I'll go with 5pm.


Quoting NCHurricane2009:
99-L....in da house...
90-L....in da house...
We need stewart at the NHC tonight so we can raise the roof!

Yes...yes...we also need DJ DMAX to make this a parrrtaeee!
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99L has a closed circulation now, all that is needed is convection, which will happen during DMAX...

My Proof
Disable the first 7 frames of the Loop, by clicking on them, and then speed up the loop to full speed. Obvious closed circulation.
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Quoting NCHurricane2009:

Why y'all not sleepin'? I got plenty last night...but I was exhausted from work last week...

Because uh... I am a night owl who likes to stay up late. I still get sleep on weekdays and do fine in school so I'm good. I am exhausted from blogging too much, now that is something that really takes a lot of energy out of ya.
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Quoting KoritheMan:

Well, 99L is a bit further north than the 1932 hurricane was. But it's possible I suppose.
That was a bad one here Kori.
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Quoting wxchaser97:

You're not the only one who got little sleep last night. I took a nap today, don't make fun of that, so I'm well rested for tonight. I am pretty sure we should see classification tomorrow and Monday morning at the very latest.

Why y'all not sleepin'? I got plenty last night...but I was exhausted from work last week...
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99L:



90L:

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Quoting Slamguitar:


I literally got no sleep last night, so I'm glad these are relatively coherent sentences.

You do have a point though. Significant convection will start to take place at Dmax and will have to persist at least into the afternoon/evening. I'll go with 5pm.

You're not the only one who got little sleep last night. I took a nap today, don't make fun of that, so I'm well rested for tonight. I am pretty sure we should see classification tomorrow and Monday morning at the very latest.
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99-L....in da house...
90-L....in da house...
We need stewart at the NHC tonight so we can raise the roof!
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Quoting wxchaser97:

I am going to go with 24hrs(11pm tomorrow) for classification. The NHC would want convection to persist for a little while before classifying 99L as a TD. More convection is all it needs as it already has a great structure and circulation.

Not to be mean, it is DMAX that increases convection and DMIN decreases it.
EDIT: I see you already corrected it.


I literally got no sleep last night, so I'm glad these are relatively coherent sentences.

You do have a point though. Significant convection will start to take place at Dmax and will have to persist at least into the afternoon/evening. I'll go with 5pm.
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Quoting Slamguitar:
Should have a TD tomorrow morning or afternoon at the latest. 99L is becoming pretty defined, and when Dmin comes around our invest should put up significant convection to make a case at classification.

I am going to go with 24hrs(11pm tomorrow) for classification. The NHC would want convection to persist for a little while before classifying 99L as a TD. More convection is all it needs as it already has a great structure and circulation.

Not to be mean, it is DMAX that increases convection and DMIN decreases it.
EDIT: I see you already corrected it so nevermind.
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18Z GFS ensemble spread








Have a good night!
Member Since: August 19, 2006 Posts: 13 Comments: 15666
Should have a TD tomorrow morning or afternoon at the latest. 99L is becoming pretty defined, and when Dmax comes around our invest should put up significant convection to make a case at classification.
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Quoting HurrAndrew:


It would have to be 3 consecutive, 2009 had like 9 or 10 storms only.

'10 = Tomas
'11 = Sean (19th)
'12 = Possibly 99L

No hate, just bringing love.

LOL...I can't believe I screwed up like that...thx for correcting!
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Quoting GTcooliebai:
Grothar what do you think 99L could take a track similar to this storm or too far west?

Well, 99L is a bit further north than the 1932 hurricane was. But it's possible I suppose.
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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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