99L a heavy rainfall threat for Jamaica, Haiti, and Eastern Cuba

By: Dr. Jeff Masters , 2:35 PM GMT on October 21, 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 have a good degree of spin. These thunderstorms are beginning to organize into spiral bands, as seen on visible satellite loops. However, the amount of heavy thunderstorm activity is about the same as yesterday, and there are no signs of a surface circulation. An Air Force hurricane hunter aircraft is scheduled to investigate 99L this afternoon, but I expect this flight will be rescheduled for later.


Figure 1. Morning satellite image of Invest 99L.

Forecast for 99L
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. On Wednesday, a strong trough of low pressure to the north of 99L is expected to turn the storm to the north or north-northeast, which should put 99L in the vicinity of Jamaica on Wednesday and Eastern Cuba on Thursday. By Friday, 99L should be in the Central or Eastern Bahamas. It is unclear at this point whether or not the trough pulling 99L to the north will be strong enough to pull the storm all the way out to sea to the northeast; a narrow ridge of high pressure has the potential to build in over 99L late this week and force the storm west-northwest, with a potential threat to the western Bahamas and U.S. East Coast by next weekend. In their 8 am EDT tropical weather outlook, NHC gave 99L a 70% chance of developing into a tropical cyclone by Tuesday morning. 99L will be capable of bringing heavy rains of 5 - 10 inches, with isolated amounts of up to 15 inches in mountainous areas, to Jamaica and Haiti, Monday through Wednesday. Heavy rains will begin on Tuesday in Eastern Cuba, and spread northwards into the Central and Eastern Bahamas by Wednesday.

Invest 90L in the middle Atlantic
A tropical wave (Invest 90L) about 830 miles east-northeast of the northernmost Lesser Antilles Islands is headed west-northwest at about 10 mph. The disturbance has a small 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 providing 90L the spin it needs to become a tropical cyclone, but is also pumping cool, dry air into the disturbance, which will keep any development slow over the next few days. Wind shear is a moderate 10 - 20 knots, and is forecast to remain in the moderate range until Tuesday. This may allow for some slow development of 90L before it encounters high wind shear of 20 - 30 knots on Tuesday night through Thursday. None of the reliable computer models develop 90L into a tropical cyclone, and it's unlikely that 90L will affect any land areas. In their 8 am EDT tropical weather outlook, NHC gave 90L a 30% chance of developing into a tropical cyclone by Tuesday morning.

The next name on the list of Atlantic tropical storms for 2012 is Sandy.

Jeff Masters

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Quoting MAweatherboy1:
Correct me if I'm wrong but this looks like a westward shift on the GFS, it's brushing the Carolinas:


You are correct, the GFS has shifted west toward the US.

Quoting TropicalAnalystwx13:
An October hurticane hit here in NC would be very rare but cool.

It would be pretty cool and a sight to see. I do have one question, what is a hurticane? I know you meant hurricane I'm just playing.
Member Since: March 16, 2012 Posts: 127 Comments: 7958
120. beell

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This may go up the East Coast:

Member Since: February 11, 2012 Posts: 84 Comments: 7946
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I still think 90L will develop. What is it missing?

Member Since: February 11, 2012 Posts: 84 Comments: 7946
As we start to get out in time the GFS moves 99L west and then to the north. It could be a nor'easter this run.
162hrs:
Member Since: March 16, 2012 Posts: 127 Comments: 7958
Quoting TropicalAnalystwx13:
An October hurticane hit here in NC would be very rare but cool.
Gee, I didn't know that hurticanes were painful. {sarcasm}
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Does anyone think we will make it to Tony?
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Correct me if I'm wrong but this looks like a westward shift on the GFS, it's brushing the Carolinas:

Member Since: February 11, 2012 Posts: 84 Comments: 7946
An October hurricane hit here in NC would be very rare but cool.
Member Since: July 6, 2010 Posts: 113 Comments: 32525
Quoting NCHurricane2009:

This could be the ultimate October 'cane...sorta like King for Florida...& Hazel or Hugo for the Carolinas...

But honestly this is still a bit out in "dreamland" time where the models aren't that accurate...so at most we should be aware and that's about it...


Absolutely, the models cannot be trusted.....yet.
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156 hours on the GFS:

Member Since: February 11, 2012 Posts: 84 Comments: 7946
Quoting Dakster:


Straight to Charleston, SC.

This could be the ultimate October 'cane...sorta like King for Florida...& Hazel or Hugo for the Carolinas...

But honestly this is still a bit out in "dreamland" time where the models aren't that accurate...so at most we should be aware and that's about it...
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106. beell
Quoting KEEPEROFTHEGATE:
i don't make em beell i just post em


LOL.
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36 Tazmanian: Are you too lazy to do that on your own?

It takes a while before ya c'n figure out where the models are comin' from, Taz. It ain't like WUbers post links to the model sites along with the model-images.
And the sites tend to be difficult to navigate through unless ya know the particular jargon (or address syntax) used by the particular site.
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104. beell


10/21 12Z GFS 700mb - Valid Wednesday, 18Z

What's a monsoon depression/Dr. Steve Lyons, May 2007

...The term has gained ascendancy in use to refer to a broad tropical cyclonic circulation characterized by 1) its large size, where the outermost closed isobar may have a diameter on the order of 600 n mi (1000 km); 2) a loosely organized cluster of deep convective elements, which may form an elongated band of deep convection in the east semicircle; 3) a low- level wind distribution that features a 100 n mi (200 km) diameter light-wind core, which may be surrounded by a band of gales or contain a highly asymmetric wind field; and 4) a lack of a distinct cloud system center. Most monsoon depressions that develop in the western North Pacific eventually acquire persistent central convection and accelerated core winds, marking their transitions into conventional tropical cyclones...

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Quoting ProgressivePulse:


What's the heading at that point?


Straight to Charleston, SC.
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hr 144 final

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hr 138

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Quoting ProgressivePulse:


What's the heading at that point?


quasi stationary it appears
just sitting there
deciding which way to go
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Quoting Grothar:
I posted these earlier. GFDL at 126 hours



The model for Florida doom...

Btw, wsw is actually predicted by some of the models, key is going to be where and when the center forms. Plus how deep the cyclone becomes, especially since the BAM model suite is not in complete agreement. All of this is subject to huge errors and changes.
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Quoting ProgressivePulse:


What's the heading at that point?

It basically stalls off the coast of Florida at this point and slowly strengthens.
Member Since: March 16, 2012 Posts: 127 Comments: 7958
hr 132

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Quoting KEEPEROFTHEGATE:
hr 120



What's the heading at that point?
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hr 126

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hr 120

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Once again the GFS has a hurricane headed toward FL. Florida needs to also watch the progress of 99L. This is at 120hrs and 989mb.
Member Since: March 16, 2012 Posts: 127 Comments: 7958
One of the 6Z ENSEMBLE!!!
Member Since: May 23, 2012 Posts: 0 Comments: 4946
hr 114

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Quoting beell:


Where's the magic trough, KEEP? Why is 99L moving N?
i don't make em beell i just post em
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hr 108

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Quoting NCHurricane2009:
some of these model runs show me something like King and Hazel combined...


Yep the overall pattern is acutally similar to that of king if you take a look. I think the fact its taking its sweet time and stronger ridging implys that florida should keeps tabs on this one.
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Quoting KEEPEROFTHEGATE:
hr 90



Where's the magic trough, KEEP? Why is 99L moving N?
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99HR!
Member Since: May 23, 2012 Posts: 0 Comments: 4946
Quoting jaxbeachbadger:
The link to models that I have been using, http://moe.met.fsu.edu/tcgengifs/, appears to be down today. Any suggestions for a different one? I've seen several on here, but if you could save me a search it would be much appreciated. Cruising next Sunday out of Port Canaveral towards the Western Caribbean.

Well I use this site to see all the models I need to see. I hope this helps you as it has plenty of different models.
Member Since: March 16, 2012 Posts: 127 Comments: 7958
Quoting NCHurricane2009:
Notice that convection picked up in the W Carib. Their has been a 2ndary surface low in that area for days left behind by the ex-Rafael cold front...


Its stealing moisture from 99L but 99L is now starting to fire some convection on its own.
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hr 96

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some of these model runs show me something like King and Hazel combined...
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hr 90

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Quoting jaxbeachbadger:
The link to models that I have been using, http://moe.met.fsu.edu/tcgengifs/, appears to be down today. Any suggestions for a different one? I've seen several on here, but if you could save me a search it would be much appreciated. Cruising next Sunday out of Port Canaveral towards the Western Caribbean.


Here you go...

Pennstate models
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hr 84

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Quoting hurricane23:


Thats why i mentioned KING in yesterdays blog. Should be interesting to watch unfold.


Hoist the shields...

I was really looking forward to making it another year without. Tis October though and arguably our most strike prone time of the year aside from September.
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Quoting jaxbeachbadger:
The link to models that I have been using, http://moe.met.fsu.edu/tcgengifs/, appears to be down today. Any suggestions for a different one? I've seen several on here, but if you could save me a search it would be much appreciated. Cruising next Sunday out of Port Canaveral towards the Western Caribbean.

It is down...
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hr 78

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Notice that convection picked up in the W Carib. Their has been a 2ndary surface low in that area for days left behind by the ex-Rafael cold front...
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hr 72

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The link to models that I have been using, http://moe.met.fsu.edu/tcgengifs/, appears to be down today. Any suggestions for a different one? I've seen several on here, but if you could save me a search it would be much appreciated. Cruising next Sunday out of Port Canaveral towards the Western Caribbean.
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12Z GFS 72HR!!
Member Since: May 23, 2012 Posts: 0 Comments: 4946

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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.