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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NAEFS model at 144 hours,850 vort..................
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Quoting Tropicsweatherpr:
I haven't see 12z GFS being posted so far. Did the model dropped it?

No, it just did the same thing it's been doing. IMO it has the best handle on things right now:



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Down to 986 mb. in 66 hrs.

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99L has come together nicely in the last 6 hours there is a hint of some type of rotation and its looking symmetrical with increasing convection. I would not be surprised if we have a TC after the HH fly out tomorrow. I'd say 50% by 2pm but knowing the NHC they probably go 40%.
Member Since: May 25, 2012 Posts: 0 Comments: 2043
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HWRF 48 hours out, intensifying Tropical Storm.


Member Since: July 8, 2005 Posts: 259 Comments: 23564
Quoting Grothar:
OH BOY, SOMEONE IS GONNA GET IT, LOOKS LIKE A REAL HEAVY RAINMAKER FOR SURE
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could the area of strong convection se of cape verdes could be another late developer and threaten the islands? could this be a repeat of TOMAS in 2010? very interesting to watch
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Quoting wxchaser97:

With this season anything is possible and I suppose Rafael could come back and regain some tropical characteristics. The GFS even brings it back to a warm core system so you never know.


And I thought he was long gone...
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Quoting Tropicsweatherpr:
I haven't see 12z GFS being posted so far. Did the model dropped it?
It still develops it and shoots the gap between Haiti and Cuba, but the images aren't updated, so here is the loop instead.
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Quoting HurricaneDean07:

Don't say the "N" word. It's bad enough to have had to deal with her for a month, note to everyone, leave her out of talk until next season. She was a headache.



The bird looking Nadine...lol
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Quoting NCHurricane2009:

Maybe its just due-diligence in tracking the remnants? Even if it tracks SE toward Europe...the warmest the waters are is 21 deg C on such a path...and I don't know if the cold core upper troughing is cold enough at those water temps for subtropical development...

With this season anything is possible and I suppose Rafael could come back and regain some tropical characteristics. The GFS even brings it back to a warm core system so you never know.
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Epac major and Atl TS
I saw something south of hawaii before this timeframe...
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Quoting CybrTeddy:


It has, go figure Nadine all over again.

Don't say the "N" word. It's bad enough to have had to deal with her for a month, note to everyone, leave her out of talk until next season. She was a headache.
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I haven't see 12z GFS being posted so far. Did the model dropped it?
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In 42 hrs. it starts deepening.

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Member Since: July 17, 2009 Posts: 69 Comments: 25304
I'm glad to see a blog topic back on the tropics.
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Quoting Astrometeor:


What is this? Cell mitosis? Biology again, huh?


90L is in the anaphase or telophase...lol
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Quoting MAweatherboy1:
I'm not sure if this has been mentioned but ATCF is giving updates on Rafael again.

Maybe its just due-diligence in tracking the remnants? Even if it tracks SE toward Europe...the warmest the waters are is 21 deg C on such a path...and I don't know if the cold core upper troughing is cold enough at those water temps for subtropical development...
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Quoting MAweatherboy1:
I'm not sure if this has been mentioned but ATCF is giving updates on Rafael again.

50 knot winds and a 970mb pressure, what's next with Rafael? I thought he was long gone but nope.
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Quoting MAweatherboy1:
I'm not sure if this has been mentioned but ATCF is giving updates on Rafael again.

AL, 17, 2012102012, , BEST, 0, 531N, 364W, 50, 970, EX, 50, NEQ, 0, 0, 280, 0,
Member Since: July 6, 2010 Posts: 113 Comments: 31417
HWRF started running on 99L:

Out to 36 hrs so far.

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30. 7544
90l not so much 99l is the one to keep one eye on starting monday if it gets close to the gulf it would easy be a track nne towards fl imo
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Quoting MAweatherboy1:
I'm not sure if this has been mentioned but ATCF is giving updates on Rafael again.


It has, go figure too. Nadine all over again.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
I'm not sure if this has been mentioned but ATCF is giving updates on Rafael again.
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Quoting Astrometeor:


What is this? Cell mitosis? Biology again, huh?

I have enough bio as it is already;) I still think 90L could develop if shear relaxes.
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99L INVEST


90L INVEST

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Thanks Doc!
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Quoting trHUrrIXC5MMX:

splitting apart


What is this? Cell mitosis? Biology again, huh?
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Quoting Ameister12:
!



We can blame Rafaels return on Ameister12 who hasn't changed his his avatar...
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Also while we have 99L and 90L lets not forget about the system in the EPAC:

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It shouldn't come as a big surprise that most of the statistical/climatology based models show a W/NW track, since that's generally what happens with these systems... the actual track should be much farther east than the consensus with these:

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Quoting CybrTeddy:
Starting to get that "look" to it, so to speak. However, we all know that storms can look impressive in the day, but by the time the sun sets, nada. However, a good sign is that convection is building as the day goes on.


Heading straight into rocket fuel as well, also note the forward speed is at 11mph, not trucking at 20mph like Ernesto and Isaac were doing. That means this is a whole different ballgame.


Interesting to see that the first model runs thinks the ECMWF/GFS is wrong, more along the lines of the CMC. It's all about timing, this time of year fronts are dipping down, and the natural progression is a hook NE. That will probably happen, but the question will be, of course, whether or not that actually happens. We will probably see Sandy/Tony from this system.
If the hook to the Northeast doesn`t happen it will move towards Yucatan right?.
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99L has the potential to be a potent system if it gets as far west as the models are showing.

Member Since: July 6, 2010 Posts: 113 Comments: 31417
All times in GMT. Derived from NHC_ATCF data for Invest99L for 20Oct.12pm
Average travel-speed&direction
between 19Oct12pm to 19Oct06pm -- 12.6km/h(07.4mph) 270.1*West
between 19Oct06pm to 20Oct12am -- 14.5km/h(09.0mph) 277.4*West
between 20Oct12am to 20Oct06am -- 20.1km/h(12.5mph) 280.7*West
between 20Oct06am to 20Oct12pm -- 22.3km/h(13.1mph) 284.5*WNWest
MHIC-SwanIsland :: AUA-Aruba :: CUR-Curacao

The longest line is a straightline projection through 99L's 2 most recent positions to its closest approach to an inhabited coastline.
99L's center was headed toward passage 25miles/40kilometres south of GreatSwanIsland
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splitting apart
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Quoting WeatherNerdPR:

Who's Rachael?

My cousin, jk, it could've been a typo.

I guess Rafael didn't want to be forgotten too easily.
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Quoting Grothar:


Wow, 97, we must have seen the same thing at the same time. :)

You know what they say, great minds think, or in this case see, alike.
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Look at what is coming off of Africa.



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Quoting Skyepony:
Thanks for the update!

We've also got a RACHAEL reprise on FNMOC/NAVY. Click pic for long JAVA loop.



Looks born again subtropical. Expected by gfs to make it back to warm core.


Who's Rachael?
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Starting to get that "look" to it, so to speak. However, we all know that storms can look impressive in the day, but by the time the sun sets, nada. However, a good sign is that convection is building as the day goes on.


Heading straight into rocket fuel as well, also note the forward speed is at 11mph, not trucking at 20mph like Ernesto and Isaac were doing. That means this is a whole different ballgame.


Interesting to see that the first model runs thinks the ECMWF/GFS is wrong, more along the lines of the CMC. It's all about timing, this time of year fronts are dipping down, and the natural progression is a hook NE. That will probably happen, but the question will be, of course, whether or not that actually happens. We will probably see Sandy/Tony from this system.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
Quoting wxchaser97:
Rafael is back up on the NAVY site.

99L.INVEST
90L.INVEST
17L.RAFAEL


Wow, 97, we must have seen the same thing at the same time. :)
Member Since: July 17, 2009 Posts: 69 Comments: 25304


Haiti, Nicaragua, Yucatan passage, Key West... take your pick.
Member Since: July 12, 2007 Posts: 0 Comments: 5995
It looks like extratropical system Rafael wants to come back South.

Member Since: July 17, 2009 Posts: 69 Comments: 25304
Rafael is back up on the NAVY site.

99L.INVEST
90L.INVEST
17L.RAFAEL
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Thanks Dr Masters.
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5. Skyepony (Mod)
Thanks for the update!

We've also got a RACHAEL reprise on FNMOC/NAVY. Click pic for long JAVA loop.



Looks born again subtropical. Expected by gfs to make it back to warm core.

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Thanks Dr. Masters!

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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.