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 GTcooliebai:
Well I'm going to call it a night. I have to be up early in the morning as I will be volunteering at the Bucs game. Have a good night everyone.

Good night GT, hopefully the weather is good where you are.
Quoting Slamguitar:


Not going to get my hopes up, but some nice huge LES flakes floating down with no wind and temps just below freezing would REALLY hit the spot for me. I'm definitely ready for winter now.

I'm ready for winter and I'm not getting my hopes up either. However there was a run, a day or so ago I think, that had 5-6" over me.
Member Since: March 16, 2012 Posts: 123 Comments: 7886
Well I'm going to call it a night. I have to be up early in the morning as I will be volunteering at the Bucs game. Have a good night everyone.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting GTcooliebai:
Thanks for posting that chart, I was looking for it through my bookmarks, but couldn't find it. Oh no I'm not saying 99L won't rapidly intensify or that it will just go kaput. For now I'll play it conservative like the rest of you and call for a strong TS/minimal hurricane, until I see how the storm interacts with the front and if shear impinges on it.


Here is the website just in case you can't find it, Link. If shear doesn't hinder intensification then this could get higher than a category 1 hurricane. The latest GFS is interesting with bringing 99L closer to Fl, like the CMC. It will be an interesting week no matter what.
Member Since: March 16, 2012 Posts: 123 Comments: 7886
Quoting wxchaser97:


Last year Major Hurricane Rina underwent rapid intensification with instability around the same as this year. I'm not saying 99L will bomb out but it won't remain weak. We still have lots to learn about hurricanes/Tropical storms and how they form.

Thanks for posting that chart, I was looking for it through my bookmarks, but couldn't find it. Oh no I'm not saying 99L won't rapidly intensify or that it will just go kaput. For now I'll play it conservative like the rest of you and call for a strong TS/minimal hurricane, until I see how the storm interacts with the front and if shear impinges on it.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
I have finished my forecast graphic that will go into my blog. It now includes a threat level category to go along with the rating scale. The track shown for 99L is not certain. My probability chances for 99L are 80% and 90L is at 40%, I will have the blog out soon.
Member Since: March 16, 2012 Posts: 123 Comments: 7886
Quoting GTcooliebai:
Hi Sar long time no see, how have you been? I think you might have a point when it comes to not understanding all of the conditions that are needed to make a TC bomb out. Vertical Instability throughout the season and for that matter even last year have been below normal.


Last year Major Hurricane Rina underwent rapid intensification with instability around the same as this year. I'm not saying 99L will bomb out but it won't remain weak. We still have lots to learn about hurricanes/Tropical storms and how they form.

Member Since: March 16, 2012 Posts: 123 Comments: 7886
Quoting sar2401:

Yeah, yeah, the old "rocket fuel" theory. :) Isaac and Ernesto spent plenty of time over waters with at least as high in TCHP numbers as 99L and not much came of it in terms of intensity. I really do think that years develop patterns. In 2005, anything that even looked like a low turned into a TC. This year, we can't get much going, even with the conditions supposedly as good as we had in 2005. We certainly don't understand all the conditions needed for TC development, and something is happening this year that's really unusual.


Ernesto was a big storm, and it may have intensified in time. However, Ernesto did "benefit" from the warm waters in terms of total energy transfer. Also, recall that the warm temps were surface temps only.
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Quoting wxchaser97:
While this is 180hrs out, I want to point out what is going on here. We had a hurricane come close to FL before being pushed off to the west some. The trough comes down into the Great Lakes providing cold air, I get a couple inches of snow from this. We then get Sandy(or her extra-tropical part), another low just to the north, and the low over the Great Lakes sorta connected together when you look at the isobars.

This isn't the first run to show snow in SE MI.


Not going to get my hopes up, but some nice huge LES flakes floating down with no wind and temps just below freezing would REALLY hit the spot for me. I'm definitely ready for winter now.
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Quoting sar2401:

Yeah, yeah, the old "rocket fuel" theory. :) Isaac and Ernesto spent plenty of time over waters with at least as high in TCHP numbers as 99L and not much came of it in terms of intensity. I really do think that years develop patterns. In 2005, anything that even looked like a low turned into a TC. This year, we can't get much going, even with the conditions supposedly as good as we had in 2005. We certainly don't understand all the conditions needed for TC development, and something is happening this year that's really unusual.
Hi Sar long time no see, how have you been? I think you might have a point when it comes to not understanding all of the conditions that are needed to make a TC bomb out. Vertical Instability throughout the season and for that matter even last year have been below normal.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
While this is 180hrs out, I want to point out what is going on here. We had a hurricane come close to FL before being pushed off to the west some. The trough comes down into the Great Lakes providing cold air, I get a couple inches of snow from this. We then get Sandy(or her extra-tropical part), another low just to the north, and the low over the Great Lakes sorta connected together when you look at the isobars.

This isn't the first run to show snow in SE MI.
Member Since: March 16, 2012 Posts: 123 Comments: 7886
Quoting AussieStorm:

I was thinking more like a cricket bat. Just joking.

A lot of moisture in the Carib right now all associated with 99L but it need to consolidate.



The front pushing into the Gulf has lots of dry air with it. Our low humidity in central Alabama today was 19%, which is an amazingly low number for us. There's also another slug of dry air approaching from the central Atlantic. All this dry air is going to be a major inhibiting factor in getting convection restarted in 99L. Depending on how long it wanders in the eastern Caribbean, the dry air will either kill it off or push whaterever does form towards Central America. I don't think the models are doing a good job of dealing with these dry air masses.
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843. 7544
hmm gfs has really shifted west now almost same aqs the cmc could this be fl trick or treat strom afterall getting interesting maybe tom. it will have fl as the bulls eye
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Quoting CybrTeddy:


Patience, the Eastern Caribbean is a graveyard, but Isaac and Ernesto were two totally different ballgames. This one is going to stall out over an area of very high TCHP. Even the UKMET is saying intensification, which is saying something.

Yeah, yeah, the old "rocket fuel" theory. :) Isaac and Ernesto spent plenty of time over waters with at least as high in TCHP numbers as 99L and not much came of it in terms of intensity. I really do think that years develop patterns. In 2005, anything that even looked like a low turned into a TC. This year, we can't get much going, even with the conditions supposedly as good as we had in 2005. We certainly don't understand all the conditions needed for TC development, and something is happening this year that's really unusual.
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0z GFS at 144 hrs. has a hurricane in the Bahamas.

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Almost looks like a stall, won't be good news for S. Fl. if 1 more degree to the west.
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Quoting NCHurricane2009:

Ouch...your humor hits like a dagger...

I was thinking more like a cricket bat. Just joking.

A lot of moisture in the Carib right now all associated with 99L but it need to consolidate.


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hr 144 final

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Looking at the shortwave Ir post (826), it appears 99L is close to the 84 hrs GFS and moving west at a decent clip. So would seem to invalidate that run to me.
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Quoting sunlinepr:

Something appears to be seriously wrong with the NHC enhanced infrared. Not only is it missing a lot of frames, but it's showing what appears to a mass of convection that doesn't exist on any of the other satellite photos I've looked at.
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Quoting sar2401:
Well, the DMIN sure killed off all the convection in 99L. If something doesn't start to break loose by tomorrow morning, there's not going to be much for the HH's to look at. I'm probably wrong, but I just don't have much faith in 99L. This area has been a storm graveyard this year, and I think it will continue. We'll see come sunrise.


Patience, the Eastern Caribbean is a graveyard, but Isaac and Ernesto were two totally different ballgames. This one is going to stall out over an area of very high TCHP. Even the UKMET is saying intensification, which is saying something.
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hr 132

Member Since: July 15, 2006 Posts: 165 Comments: 52260
Well, the DMIN sure killed off all the convection in 99L. If something doesn't start to break loose by tomorrow morning, there's not going to be much for the HH's to look at. I'm probably wrong, but I just don't have much faith in 99L. This area has been a storm graveyard this year, and I think it will continue. We'll see come sunrise.
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hr 120

Member Since: July 15, 2006 Posts: 165 Comments: 52260
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Quoting mitthbevnuruodo:
Anyone have any luck with the meteor shower tonight? I got home from work just before 2am, collected my daughter and camera, as was actually clear from once here....but only saw a handful over an hour and a half. They were pretty long ones, but was really hoping for a good display being the other ones this year have been cloudy here! None of them happen in frame of camera either doh! LOL Ah well, she was happy with the few bigger ones we saw at least!

No stars falling on Alabama so far either. It's still a few hours until the theoretical maximum but I saw one in the past hour, so it's not looking hopeful.
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108 hr

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You've all been teasing with the forecast maps all week...be interesting to see if it does anything like the ones that were way to far ahead to take serious! Hope nothing too bad for them islands though.
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Anyone have any luck with the meteor shower tonight? I got home from work just before 2am, collected my daughter and camera, as was actually clear from once here....but only saw a handful over an hour and a half. They were pretty long ones, but was really hoping for a good display being the other ones this year have been cloudy here! None of them happen in frame of camera either doh! LOL Ah well, she was happy with the few bigger ones we saw at least!
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hr 96

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hr 84

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hr 72

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Quoting TropicalAnalystwx13:

Scratch that.

Tomorrow at 21:00Z (5:00 p.m. EDT).


Well, that works less to the favor of my 5pm TD classification prediction.
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hr 60

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hr 48

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hr 36
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24 hr

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Quoting Slamguitar:


Thanks!



You and me both. ;)

Scratch that.

Tomorrow at 21:00Z (5:00 p.m. EDT).
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00z gfs 12hr to 144

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Quoting TropicalAnalystwx13:

18z (2:00 p.m. EDT).


Thanks!

Quoting HurricaneDean07:

I say they call 99L, TD 18 tomorrow at 5 pm advisory.


You and me both. ;)
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Quoting Slamguitar:
What time in the afternoon are they sending the HH out?

18z (2:00 p.m. EDT).
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Quoting wxchaser97:

Only for the moment, 99L will increase it's convection.


99L tomorrow and they could find a TD.

I say they call 99L, TD 18 tomorrow at 5 pm advisory.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Convection continues to popcorn and refire
Member Since: October 3, 2010 Posts: 40 Comments: 4129
What time in the afternoon are they sending the HH out?
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Quoting NCHurricane2009:
For the moment...ex-Rafael has more convection than 99L:

http://www.ssd.noaa.gov/goes/east/natl/avn-l.jpg

Only for the moment, 99L will increase it's convection.

Quoting NCHurricane2009:

Recon is investigating 90L or 99L?

99L tomorrow and they could find a TD.
Member Since: March 16, 2012 Posts: 123 Comments: 7886
For the moment...ex-Rafael has more convection than 99L:

http://www.ssd.noaa.gov/goes/east/natl/avn-l.jpg
Member Since: September 15, 2009 Posts: 391 Comments: 3519
For those who missed it earlier, I did a blog update on the tropics.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.