Isaac is strengthening

By: Dr. Jeff Masters , 2:58 PM GMT on August 24, 2012

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Tropical Storm Isaac is strengthening. An Air Force Reserve hurricane hunter aircraft measured surface winds of 60 mph on the east side of the center, about 170 miles south of Santo Domingo in the Dominican Republic, at 8:40 am EDT this morning. Winds at the aircraft's flight level of 5,000 feet were hurricane force, 76 mph. The surface pressure remained fairly high, at 1000 mb. Tropical cyclones have a warm core, and the Hurricane Hunters typically find that a storm's lowest pressure is also where the warmest temperature are. However, this morning's flight found that Isaac was still disorganized, with the storm showing almost no evidence of a warm core. Isaac's warmest temperatures were displaced 75 miles to the west of where the lowest pressure was. There were no signs of an eyewall beginning to build. Infrared and visible satellite loops show that Isaac is somewhat asymmetric, with a large band of intense thunderstorms to the east, separated from the core region. This is interfering with both the storm's low-level inflow and upper-level outflow, but the band appears to be dying out. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south.


Figure 1. Evening shot of Tropical Storm Isaac taken on August 23, 2012, by the NOAA Hurricane Hunters.

Isaac's rains
Radar imagery from Puerto Rico shows that Isaac is dumping some very heavy rains to the south and east of the center. Ponce, Puerto Rico had a wind gust of 37 mph this morning as a heavy band of rain moved through, and radar-estimated rainfall amounts are in excess of 7 inches for the region just north of Ponce. Power outages to 2,000 homes have been reported in Puerto Rico this morning. NOAA buoy 42085 offshore from Ponce reported a wind gust of 54 mph near 9 am EDT this morning. Rainfall estimates from microwave satellite instruments suggest that Isaac's heaviest rains are to the south of the center, and that the Dominican Republic and Eastern Haiti will escape the worst of Isaac's rains. Haiti's southwest peninsula and Eastern Cuba should suffer the heaviest rains.


Figure 2. Radar-estimated precipitation from the Puerto Rico radar shows the region near Ponce has received up to 7" of rain as of 10 am EDT August 24, 2012.

Latest model runs for Isaac
The latest set of 00Z and 06Z (8 pm and 2 am EDT) model runs have come into better agreement, thanks to the dropsonde mission by the NOAA jet yesterday afternoon and evening. Isaac should move over Haiti's southwest peninsula and then eastern Cuba, then track along the spine of Cuba before popping off into the Florida Straits on Sunday. A trough of low pressure will then pull Isaac to the northwest, and then north, towards the Central Gulf Coast. Landfall locations range from Mississippi (06Z HWRF model run) to the Florida Panhandle south of Tallahassee (06Z GFDL model run.) It is possible that the trough of low pressure pulling Isaac to the north may not be strong enough to pull Isaac all the way to the northeast and out to sea, and the ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.


Figure 3. Predicted 5-day rainfall total ending at 2 am EDT Wednesday August 29, from Tropical Storm Isaac. Graphics were generated from the 6Z (2 am EDT) August 24, 2012 run of the HWRF model. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.

Intensity forecast for Isaac
Isaac has not intensified as much as predicted, and I think that the storm's very large size is partially responsible for that. It's tough to spin up as much atmosphere as Isaac is attempting to do very quickly. Conditions remain favorable for intensification today, with wind shear low, 5 - 10 knots, ocean temperatures warm, 29°C, and dry air mostly mixed out of the storm's core. The large band of intense thunderstorms to the east, separated from the core region, appears to be dying out now, which will help the storm grow more organized. The storm's structure has improved considerably between 9 am - 10 am EDT, with a fairly tight center forming, exposed to view, on the north edge of Isaac's heaviest thunderstorms. A curved band of heavy thunderstorms is now trying to wrap around this center to the northeast, and this band will bring very heavy rains to Haiti and the Dominican Republic this afternoon. I expect that the Hurricane Hunters will observe a partial eyewall in their vortex reports between 2 - 4 pm EDT this afternoon. The storm's large size and disorganized structure suggests that Isaac will be able to intensify only slowly today, and will have top winds of 70 - 75 mph before encountering Southwest Haiti and Eastern Cuba tonight and Saturday. Isaac will likely be a 50 - 60 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate. The upper-level wind pattern favorable may be quite favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm--though the models disagree on whether or not this anticyclone will set up directly over Isaac or not. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 17% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. Tampa is in the NHC cone of uncertainty, though near the edge of it. At a minimum, Tampa will receive very heavy rains and wind gusts in excess of 40 mph. Isaac is going to be hard-pressed to bring hurricane-force winds to the city, though, since any path that takes it close to Tampa would keep the storm too close to land for significant intensification to occur. I put the odds of a mass evacuation being ordered for Tampa during the convention at 1%. I have detailed information on Tampa's storm surge vulnerability in a post from last week.

Invest 97L off the coast of Africa
A tropical wave that moved off the coast of Africa on Thursday has been designated Invest 97L by NHC this morning. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear of 10 - 20 knots. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Sunday morning. The 8 am EDT SHIPS model forecast predicts that 97L will track west-northwest over the next few days, and encounter a region of high wind shear associated with an upper-level low on Monday and Tuesday. This low may be capable of tearing the storm apart, as happened to Tropical Storm Joyce. None of the models currently foresee that 97L will affect the Lesser Antilles Islands, but 97L may pass near Bermuda 7 - 8 days from now.



20th anniversary of Hurricane Andrew
Today, August 24, is the 20th anniversary of Hurricane Andrew, which hit South Florida as a Category 5 hurricane with 175 mph winds--one of only three Category 5 hurricanes ever to hit the U.S. With Isaac churning through the Caribbean this week, I didn't have time to prepare a special post on Andrew, but our Hurricane Andrew archive page has links to satellite and radar images, newspaper headlines, and 49 YouTube videos. Here's an additional link for an Andrew damage video shot by wunderblogger/storm chaser Mike Theiss, when he was 14 years old.

Jeff Masters

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Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.


no way.... we will see what the death toll is.
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Quoting Stormchaser121:

ERUO model still saying western gulf?? I still think its correct.

Yesterday's model, most recent was 00z
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Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.


I constantly worry about Haiti. As I have said before, I would prefer a stronger storm striking us, if it means Haiti doesn't get more than a menial amount of rain and wind.
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Quoting Stormchaser121:

ERUO model still saying western gulf?? I still think its correct.


Not out yet.
Member Since: February 6, 2010 Posts: 0 Comments: 214
Quoting FLWeatherFreak91:
I personally know people who had no idea about Isaac until today lol


I had one say it was going to Houston, talk about not staying informed.
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Quoting SFLWeatherman:
I say Tropical Storm Watch will go up for are of SE FL at 2PM


rarely ever at the intermediate advisories. Always the 5's and 11's. It was designed to play to the news cycles. 6am 12pm 6pm and 11pm news.
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HH should have been out by now. I guess looking at it in another way... I prefer from them to be late and in working order than going out and having to go back for service.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
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T.C.F.W.
09L/TS/I/CX
MARK centre of image
17.00N/70.00W
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Quoting flowrida:
What would happen to the tampa bay area if Issac was a cat 2 right off the coast, say 40 miles?


It would be the most action they've seen since TS Debby in June.
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Sunday Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rain. Partly sunny, with a high near 87. Windy, with a east wind 28 to 31 mph, with gusts as high as 44 mph. Chance of precipitation is 60%.
Sunday Night Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rain. Mostly cloudy, with a low around 80. Windy, with a east wind 34 to 37 mph, with gusts as high as 50 mph. Chance of precipitation is 70%.
Monday Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rain. Cloudy, with a high near 90. Windy, with a southeast wind around 30 mph, with gusts as high as 41 mph. Chance of precipitation is 60%.
Monday Night A 40 percent chance of rain and thunderstorms. Mostly cloudy, with a low around 80. Windy, with a south wind around 24 mph, with gusts as high as 33 mph.



thats for dade county schools should be closed buses wont run
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Quoting HoustonTxGal:
12z ECMWF


ERUO model still saying western gulf?? I still think its correct.
Member Since: September 2, 2011 Posts: 0 Comments: 1140
New Euro comes out shortly right? I'm guessing we will see a east shift, but who knows
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Quoting ncstorm:
12z precip map

through 120 hours


through 240 hours


Enough with the rain already!!
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Quoting SFLWeatherman:
N of all of them


Official fix might have overshot north by a few tenths.

Colorado state automated tracker has it back down to 15.7N and 71.2W in the latest frame.



It may be over correcting in the opposite direction, so if you take a compromise you're still back at 16N, which is still SW of those model runs by a few tenths.

Member Since: January 25, 2012 Posts: 32 Comments: 1499
593. MTWX
Quoting WaterWitch11:


applause :)

when was the last time the weather channel was in cuba?


This is the first time according to Cantore...
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right looking at it again I'd say 16.2N 70.9W and convection is starting to wrap around already on its E and NE sides wrapping around from NE side
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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MIAMI FL
1231 PM EDT FRI AUG 24 2012

FLZ068-168-241700-
COASTAL PALM BEACH COUNTY FL METRO PALM BEACH COUNTY FL
1231 PM EDT FRI AUG 24 2012

...A SIGNIFICANT WEATHER ADVISORY IS IN EFFECT FOR EASTERN PALM BEACH
COUNTY...FOR GUSTY WINDS OF 45 TO 55 MPH...

* UNTIL 100 PM EDT

* AT 1230 PM EDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
STRONG THUNDERSTORM NEAR PALM BEACH...AND MOVING WEST AT 15 MPH.

* THE STORM WILL AFFECT...
PALM BEACH...
WEST PALM BEACH...
GLEN RIDGE...
PALM SPRINGS...
HAVERHILL...
GOLDEN LAKES...
AND SURROUNDING COMMUNITIES.

THE PRIMARY IMPACTS WILL BE GUSTY WINDS OF 45 TO 55 MPH. THESE WINDS
CAN DOWN SMALL TREE LIMBS AND BRANCHES...AND BLOW AROUND UNSECURED
SMALL OBJECTS. SEEK SHELTER IN A SAFE BUILDING UNTIL THE STORM
PASSES.

LAT...LON 2662 8004 2661 8003 2659 8020 2678 8019
2680 8003 2666 8003 2665 8003 2663 8003
TIME...MOT...LOC 1631Z 081DEG 15KT 2670 8003

$$
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Quoting floridaboy14:
umm... i dont know what your seeing but he is moving wnw
look at visible images it looks like a jog or slight movement to the NW or it can be the convection fooling our eyes
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Quoting Seflhurricane:
the nhc says WNW but the last few visible frames shows a NW motion



yep but theese storms do wobble expect a west wobble near Hati JMO
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Quoting Hurricane1956:
I heard that Miami Dade County is going into Alpha Bravo emergency in preparation for Isaac.
this is going to be an experience for all of us in florida huh
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Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.
Only takes a Category One to cause 1,000+ deaths in Haiti. That's more than 90% of hurricanes that will ever hit USA. This isn't all-American blog.
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Quoting emguy:
This is real news...not a joke. The Weather Channel is going international with deploying broadcast teams into hurricanes. They just announced that Mike Sidell is already in Cuba. It's their first intenational deployment of crews into hurricanes.


applause :)

when was the last time the weather channel was in cuba?
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Quoting FLWaterFront:


I honestly doubt that anyone who reads this blog would get that impression. Maybe there are plenty of people in the general populous who think this way but I would doubt that as well, at this point. This is the Information Age and anyone who has ever seen a local television news presentation in the Tampa Bay area knows that hurricanes are an issue here because the local media and local governments drive home the point all the time.
I personally know people who had no idea about Isaac until today lol
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Quoting RTSplayer:
Quoting Msdrown:
Alright the TWC just showed the GFS taking the storm up the east coast of fl. You have most models showing similar except the out flyer european. What is the best bet? When will that High in the centra GOM move out and how will that affect the track??


No it doesn't.

The consensus on the GFS is west coast.

It still has at least one ensemble member as far west as the Mouth of the Mississippi, and a couple members still cut LEFT hooks after landfall.


I wish people would pay closer attention to the most recent updates. The last GFS on the East Coast must have been like 48 hours ago...I don't know I forget...


My BUST I met West Coast Fla. I'm in MS and in the so called cone. With the outflyer european more my way. Sorry for the side.
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583. MTWX
Quoting southfla:


Of course follow the NHC guidelines, but here is what I do.

When a Public Advisory comes out it will normally give you the distance from the storm, the extent of tropical storm force winds and the speed. So look for three pieces of information. You will want to use nm and mph or km and km/h. Don't mix the two.

1) LOCATION...16.3N 70.8W ABOUT 185 MI...300 KM SSE OF PORT AU PRINCE HAITI

2) TROPICAL STORM FORCE WINDS EXTEND OUTWARD< UP TO 185 MILES...295 KM
FROM THE CENTER.

3) PRESENT MOVEMENT...WNW OR 295 DEGREES AT 14 MPH...22 KM/H

Clearly in Haiti they should be prepared by now since tropical storm force winds extend 185 miles and the storm is about 185 miles from Port Au Prince.

-------------------
Step 1: number of miles from storm center minus number of miles the tropical storm force winds extend in Haiti's case 185 -185= 0. They are about out of time to prepare.

Step 2: divide the storm's speed along the track (not the wind speed) by the number of miles in step 1.

This will give you approximately the number of hours until tropical storm force winds reach your area.

Say you live in Key West and the advisory tomorrow morning says Issac is 500 miles SSE of Key West. The tropical force winds extend 150 miles and the speed is 15 mph.

500-150 = 350 miles from the approximate edge of tropical force winds.

350 miles divided by 15 mph = 23 hours. That is the approximate number of hours before it would be too windy to put up shutters, but I would add some time in case the forward speed increase or the tropical storm force winds move out further.

This just gives you a rough guide -- but always follow the recommendations of official agencies. You can play with the speed and extent of tropical force winds to give yourself some wiggle room.


Unfortunately they don't really have any ability to prepare in Haiti... :(
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Quoting SFLWeatherman:
it so going NW!!
umm... i dont know what your seeing but he is moving wnw
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Quoting SFLWeatherman:
I say Tropical Storm Watch will go up for are of SE FL at 2PM
very likely , would not be surprised if a hurricane watch is issued for the florida keys
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Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.


How so? How many Gulf Coast residents live in tents???
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What would happen to the tampa bay area if Issac was a cat 2 right off the coast, say 40 miles?
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Selected Florida school districts / Monday (8/27) school status

Broward County Schools / Undecided
Charlotte County Schools / No word
Collier County Schools / Undecided
Hillsborough County Schools / No word
Lee County Schools / Unbdecided
Manatee County Schools / Undecided
Miami-Dade Schools / No word
Monroe County Schools / Closed
Palm Beach County Schools / No word
Pinellas County Schools / Undecided
Sarasota County Schools / Undecided
Member Since: November 8, 2009 Posts: 4 Comments: 13260
Quoting Bluestorm5:
Really? 5+ is getting off people's backs? I'm just saying people are too focusing on USA when we should be worried for Haiti as well.


I totally agree. There are hundreds of thousands of people living in tents and sub-standard housing that will soon be in tropical storm conditions. This is a humanitarian nighmare, and I hope everyone is thinking of donating to portlight...
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Quoting SFLWeatherman:
it so going NW!!
the nhc says WNW but the last few visible frames shows a NW motion
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Quoting Msdrown:


The TWC just showed the (3-4day isobar type) progression of the GFS and they took it up the west coast my bust on sides. I'm trying to figure out if its a long shot for the European direction over here towards MS.


Euro looks like it begining to be the outlier to the west. Need to see some more runs to see if it shifts back east
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12z precip map

through 120 hours


through 240 hours
Member Since: August 19, 2006 Posts: 13 Comments: 13441
Quoting emguy:


Agreed! Because if they get hit as bad as I fear, this story needs to be told so people see it and help. I heard that people will not leave their tents for shelter because all of there belongings are in the tents and they do not want to leave them unattended. This is highly sad news.
My friend was in Haiti a month ago and she told me many stories about Haitians. She said they are the happiest people she've ever met and that they are graceful people.
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571. FOREX
Quoting sar2401:


I know what I read. What I read is wrong. Anyone saying that only Florida is at risk is wrong - dead wrong - at this point. We don't even know how strong the ridge will be or how strong Isaac will be. It's silly to declare the entire Gulf coast out of danger when the storm is still south of Hispanola.


Justin Kiefer, the Chief MET on WJHG in Panama City Beach just said that it is looking more and more likely that Isaac will be pulled Northeast of the PC Beach area and that we might get a lot of rain, but not a lot of wind. I'm starting to feel a lot better.
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I say Tropical Storm Watch will go up for are of SE FL at 2PM
Member Since: May 23, 2012 Posts: 0 Comments: 4207
Quoting E46Pilot:
I don't put up shutters unless it is at least a category 2 storm, and is predicted to hit in less then 24 hours.


I'm in Homestead/Miami area and I do the same....we'll have enough time to close up shutters if it gains strength once it crosses Cuba....here is to hoping I don't!
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Quoting Seflhurricane:
looking at visible images it appears Isaac is making a jog to the NW , will be very intresting to see if this trend continues but very impressive on visible images


ya first time Ive seen the sat since this morning looks to be alittle more north oh and any1 gota link the levis tidbit ty
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Quoting LargoFl:
this cmc model has miami in its sights huh
I heard that Miami Dade County is going into Alpha Bravo emergency in preparation for Isaac.
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566. yoboi
Quoting Bluestorm5:
That's nice to hear that. Someone should be in Haiti as well.


potter is in haiti....he is from twc...
Member Since: August 25, 2010 Posts: 6 Comments: 1975
565. A4Guy
Quoting Bluestorm5:
Really? 5+ is getting off people's backs? I'm just saying people are too focusing on USA when we should be worried for Haiti as well.


What will worrying do? If we all wring our hands, will it stop the rain from falling on Haiti? If people in the FL panhandle start shaking...will it impact the path of the storm?
The best you can do is donate or volunteer your efforts after the storm passes, if you feel passionately about the issue. You can also lobby the US Gov't etc. to funnel more aid to Haiti, etc. (or wherever your passion lies).
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What is most keeping Issac from creating a better eye?
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563. DVG
Quoting cirrocumulus:


This blog is a lot better than TWC for following storms. TWC is OK for some stuff except usually they are showing stories when you need some weather. Of course now they are about to station observers out there in the "cone" and cover the same trees blowing in the wind every few minutes.


At least it's about current weather, rather than some canned programming.
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Quoting Bluestorm5:
Really? 5+ is getting off people's backs? I'm just saying people are too focusing on USA when we should be worried for Haiti as well.

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.
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Quoting SFLWeatherman:
N of all of them
if the NW jog continues or becomes a trend it will not be over cuba very long it will reemerge over the atlantic and the is high TCHP in that region and that would put more bad weather across southern florida
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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.