Isaac pounding Haiti and the Dominican Republic with torrential rains

By: Dr. Jeff Masters , 2:24 PM GMT on August 25, 2012

Tropical Storm Isaac is pounding Haiti and the Dominican Republic with torrential rains that are causing extremely dangerous flooding and landslides. Isaac's center passed over Haiti's southwest peninsula early this morning, tracking about 50 miles west of the capital of Port-au-Prince. As the center pulled away to the northwest, Isaac's heaviest thunderstorms moved ashore over Hispaniola near sunrise, and are now dumping heavy rains with rainfall rates approaching one inch per hour, according to recent microwave satellite estimates. Barahona on the south coast of the Dominican Republic had received 5.14" of rain as of 8 am EDT this morning, and it is probable that some mountainous areas in Haiti and the Dominican Republic have already received up to 10" of rain from Isaac. These rains will continue though much of the day, and have the potential to cause high loss of life in Hispaniola.


Figure 1. A river north of Port-au-Prince, Haiti in flood due to rains from Isaac. Image from Amélie Baron via Twitter.

Latest observations
Isaac built a partial eyewall last night as the storm approached Haiti, but passage over the rough mountains of Haiti has destroyed the inner core, and the surface center of the storm is now fully exposed to view on satellite images. Radar out of Guantanamo Bay, Cuba shows no sign of an organized center, but does reveal some very intense thunderstorms affecting Eastern Cuba, Western Haiti, and nearby islands. Latest data from the Air Force Hurricane Hunters confirm that Isaac has weakened; during their penetration to obtain their 7:08 am EDT center fix, the aircraft reported top surface winds of 55 mph with their SFMR instrument, top flight-level winds at 5,000 feet of 68 mph, and a pressure rise of 3 mb, to 998 mb. Infrared and visible satellite loops show that Isaac remains a large and well-organized storm, though it lacks an inner core. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is still good to the north, but is lacking elsewhere. An impressive large multi-day satellite animation of Isaac is available from the Navy Research Lab.


Figure 2. Rainfall rates estimated by the NOAA F-17 polar orbiting satellite at 6:21 am EDT August 25, 2012. Rainfall rates of 1 inch per hour (orange colors) were occurring in a large area to the south of Hispaniola, and these heavy rains have now moved onshore. Image credit: Navy Research Laboratory.

Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs are similar in spread to the previous set of runs. Our two best models, the GFS and ECMWF, are virtually on top of each other, with a landfall location in the Florida Panhandle between Fort Walton Beach and Panama City. It is likely that the trough of low pressure pulling Isaac to the north will not be strong enough to pull Isaac all the way to the northeast and out to sea, and Isaac has the potential to drop torrential rains capable of causing serious flooding over the Southeast U.S. The latest 8-day precipitation forecast from the GFS model (Figure 3) calls for 10 - 15 inches of rain over portions of Georgia and South Carolina from Isaac. The ECMWF model, however, predicts that a ridge of high pressure will build in and force Isaac to the west after landfall, resulting in a slow motion across the Tennessee Valley into Arkansas by Friday. Arkansas is experiencing its worst drought in over 50 years, so the rains would be welcome there.


Figure 3. Predicted precipitation for the 8-day period from 2 am Saturday August 25 to 2 am Sunday September 2, from the 2 am EDT August 25 run of the GFS model. This model is predicting a wide swath of 5 - 10 inches of rain (orange colors) will affect portions of Cuba, Florida, the Bahamas, and the Southeast U.S. Image credit: NOAA/NCEP.

Intensity forecast for Isaac
Isaac survived passage over Hispaniola relatively intact. It's large size aided this, and this will also help it survive passage over Cuba today and Sunday. By the time Isaac pops off the coast of Cuba into the Florida Straits on Sunday, it will likely be a 50 mph tropical storm with a large, intact circulation. Isaac will be over very warm waters of 31°C (88°F) in the Florida Straits, wind shear will be light to moderate, and the upper-level wind pattern will feature an upper-level anticyclone over the storm, aiding its upper-level outflow. As I discussed in my previous post, Crossing Hispaniola and Cuba: a history, there have been five storms since 1900 with an intensity similar to Isaac, which crossed over both Haiti and Cuba, then emerged into the Florida Straits. These five storms strengthened by 5 - 20 mph in their first 24 hours after coming off the coast of Cuba. Given the relatively intact structure of Isaac so far, and the favorable conditions for intensification, I expect Isaac will intensify by 15 - 20 mph in 24 hours once the center moves off of the north coast of Cuba. If Isaac spends a full two days over water after passing the Florida Keys, it is possible that it will have enough time to develop a full eyewall and undergo rapid intensification into a Category 2 or 3 hurricane. The latest 06Z (2 am EDT) run of the GFDL model is calling for Isaac to intensify to Category 2 strength, then weaken to Category 1 at landfall in Mississippi on Tuesday. The 06Z HWRF run is calling for landfall in the Florida Panhandle near Fort Walton Beach as a borderline Category 2 or 3 hurricane. The 5 am EDT NHC wind probability forecast gave Isaac a 19% chance of becoming a Category 2 or stronger hurricane in the Gulf. I expect these odds are too low, and that Isaac has a 40% chance of becoming a Category 2 or stronger hurricane in the Northern Gulf of Mexico. I doubt the storm has much of a chance of hitting Category 4 or 5 status, though. While the surface waters in the Gulf of Mexico are very warm, near 30 - 31°C, the total heat content of these waters is unusually low for this time of year. We got lucky with the Gulf of Mexico Loop Current this summer, as it did not shed a big warm eddy during the height of hurricane season, like happened in 2005 (I discuss this in my Gulf of Mexico Loop Current Tutorial.) Without the type of super-high heat energy we had in 2005 in the Gulf of Mexico, Category 4 and 5 hurricanes in the Gulf of Mexico in 2012 will have difficulty forming.

Invest 97L off the coast of Africa
A tropical wave (Invest 97L) is located about 350 miles west-southwest of the Cape Verde Islands off the coast of Africa. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Monday morning. The 8 am EDT SHIPS model forecast predicts moderate shear for the next 5 days over 97L, so some development is possible if 97L can fend off the dry air to its north. None of the reliable models foresee that 97L will be a threat to the Lesser Antilles Islands. However, both the GFS and ECMWF models predict that a tropical wave that has not yet emerged from the coast of Africa may develop next week, and potentially take a more westward track towards the Lesser Antilles.

The Weather Channel's hurricane expert, Brian Norcross, is now writing a blog on wunderground.com. For those of you unfamiliar with his background, here's an excerpt from his first post, from last night:

"This evening 20 years ago the sun set on the horrendous first day after Hurricane Andrew. I was in downtown Miami at the studios of the NBC station. We knew that there was "total" destruction in South Dade County, but even that didn't describe it. Here's to the people that went through it... and held their families together in a situation that most people can't imagine."

Angela Fritz will have a new post here by 6 pm EDT. For the next few days, I plan to do the morning blog post, and Angela will be doing the late afternoon post.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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Quoting E46Pilot:
I don't know if the HH can get clearance to fly in Cuban airspace. So until it comes out of their airspace I don't think they can pinpoint the exact center.
They can't drop dropsondes over land. They don't want to kill somebody.
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Quoting flcanes:
hmmm, is cantore in pensacola yet????

Too soon.
He'll show up in Tampa before that imo
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Here in St Lucie county Florida, the weather service keeps bouncing between a TS watch and a TS warning.. flip flop flip flop. I find it amusing in a way.
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Quoting KEEPEROFTHEGATE:
12z gfs init


that spells mudslides and cholera for haiti
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Quoting GTcooliebai:
GFS 12 hrs.


anything interesting so far
and is that kirk forming in the catl?????
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12z gfs init

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Quoting Seflhurricane:
from Brian Norcross a few minutes ago


Not unexpectedly, Isaac seems to be surviving its trek across Haiti with it's circulation intact. In moved just far enough west for its core to miss the highest mountains, although the Hispaniola and Cuban land masses will have some tempering effect for the next day or so. The upshot is... the Florida Keys need to get ready for hurricane conditions immediately, including 1 to 3 feet of storm surge flooding at high tides. The worst of this flooding will not occur until Monday when the storm has past and the backside winds push the water into Florida Bay.

For Miami and the entire metro area, be ready for an extended period of very bad weather with winds gusting to hurricane force... likely through Monday. Some flooding around Biscayne Bay is expected at high tide.

The bad weather has already begun in South Florida due to an upper-level feature that is helping pull Isaac north. Well more that a FOOT OF RAIN may fall between today's rain and that directly related to Isaac.

Be prepared to stay indoors in a safe building through Monday. When the wind starts blowing in earnest, stay away from windows.

More on farther up the west coast later.

See you on The Weather Channel.
hmmm, is cantore in pensacola yet????
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GFS 12 hrs.

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1500z

1000mb



990mb



970mb



950mb

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Quoting clwstmchasr:
I see that Tampa is now out of the cone. We'll get some good rains with 30-40mph winds
But hurricane watch is up nonetheless...
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Quoting sporteguy03:


Any wobble or jog to the right and it could be worse, I am now under a TS Watch in Polk County 60 miles inland.
yes same here..up to tarpon springs
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I also want to state for those on the east coast, Isaac is still going NW..until it makes that left hand turn towards the GOM, I aint sitting here thinking all is well..also, when the NHC uses the word "should turn or should steer"..take note..Ive seen that too many times where they state a cyclone should turn and it dosent..

A MID/UPPER-LEVEL TROUGH OVER THE EASTERN UNITED
STATES IS LIFTING OUT TO THE NORTHEAST AS A UPPER-LEVEL LOW MOVES
SOUTHWARD ACROSS THE CENTRAL GULF OF MEXICO. THIS EVOLUTION...
COMBINED WITH THE LOW-LEVEL RIDGE NORTH OF ISAAC...SHOULD STEER THE
CYCLONE GENERALLY NORTHWESTWARD NEAR THE NORTH COAST OF CUBA AND THE
FLORIDA KEYS DURING THE NEXT 48 HR AS INDICATED BY THE TIGHTLY-
CLUSTERED MODEL GUIDANCE.
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Quoting wpb:
low pressure system in nw carb causing shear over storm

nope, isaac is doing just fine
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from Brian Norcross a few minutes ago


Not unexpectedly, Isaac seems to be surviving its trek across Haiti with it's circulation intact. In moved just far enough west for its core to miss the highest mountains, although the Hispaniola and Cuban land masses will have some tempering effect for the next day or so. The upshot is... the Florida Keys need to get ready for hurricane conditions immediately, including 1 to 3 feet of storm surge flooding at high tides. The worst of this flooding will not occur until Monday when the storm has past and the backside winds push the water into Florida Bay.

For Miami and the entire metro area, be ready for an extended period of very bad weather with winds gusting to hurricane force... likely through Monday. Some flooding around Biscayne Bay is expected at high tide.

The bad weather has already begun in South Florida due to an upper-level feature that is helping pull Isaac north. Well more that a FOOT OF RAIN may fall between today's rain and that directly related to Isaac.

Be prepared to stay indoors in a safe building through Monday. When the wind starts blowing in earnest, stay away from windows.

More on farther up the west coast later.

See you on The Weather Channel.
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Quoting duttlyn:


Yep...

We were in Fort Myers and taking it easy because it was a cat 2 heading to Tampa! Suddenly, it was a cat 4 that jogged right and slammed right into us. When it's riding the edge of the state, it can jog and hit anywhere.
..that charley really scared me..your right WE were supposed to get him coming in on us..
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So what is everyone's take on the weather we will get here on the Space Coast? I am supposed to leave for the panhandle and was wondering how much prep should I do here first.
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Quoting wpb:
levi must be analyzing data for his post

im betting that his thinking will probably be the final track and intensity
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351. wpb
low pressure system in nw carb causing shear over storm
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GFS time!
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hmm I wounder Why NHC took off TS Watches for the Cayman Islands. on our offical national weather service website, that has just been updated and we are still under a TS watch.

by the way, just to let you guys know. it is the governments responsablity to issue watches and warnings for their perspective country, island(s), county, and state. NOT the NHC.
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Quoting LargoFl:
i hope your right, but with each new advisory, it inches closer to the right, not too long ago it was going to be 200 miles off our coast, we will see once it hits south florida and comes up the coast..IF it comes up the coast..that isnt a given just yet..small possibility it goes up the spine of florida like a few models suggest..we'll see maybe come sunday afternoon or night..im ready for it, got all the outside stuff done, didnt put plywood etc yet..waiting to see what happens


Any wobble or jog to the right and it could be worse, I am now under a TS Watch in Polk County 60 miles inland.
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Steady 15 kt wind here on marco island I'm worried about surge more than anything else my grandmothers house is just 6/7 feet above the water... Anyone have a prediction of surge here? Tia
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surfers in south florida getting ready!!
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345. 892mb
Quoting louisianaweatherguy:
wow Isaac will propbably travel on land now according to latest plot and motion... hmmm... maybe THAT'S why the models are indicating a more WNW-W track - A WEAKER storm... until the gulf that's when it should spin up and go norht to hit the panhandle... SHOULD hit the panhandle...

I'm still a little uneasy about this one for some reason....


I agree!! I'm down on Grand Isle and expecting some surge even if it hits on the Panhandle.
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Quoting E46Pilot:
Wow I don't even remember Hurricane Ernseto. Came right through here in S FL. LOL

i do, we had to move in our lawn furniture and huddle in our living room lol
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343. wpb
levi must be analyzing data for his post
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Quoting weatherh98:


Joe bastardi
Or
Justin beiber


Or Jbird :D
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Quoting SELAliveforthetropic:


Houma here.... We all should know that you never ever take your eye off of any that may get in the gulf....


Mandeville here... If this hits florabama we will get some rain.
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Quoting Jedkins01:



Punta Gorda wasn't in the cone as Charley approached.


Yep...

We were in Fort Myers and taking it easy because it was a cat 2 heading to Tampa! Suddenly, it was a cat 4 that jogged right and slammed right into us. When it's riding the edge of the state, it can jog and hit anywhere.
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Who thought 6 months ago that Brian Norcross has a blog on Wu-ground
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this is a monster, so even if it makes landfall on the east coast, the rain could still be felt in alabama and misssissippi
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Wow I don't even remember Hurricane Ernseto. Came right through here in S FL. LOL
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Quoting alvarig1263:


They are out of the cone for a direct hit, but because of the large TS force wind field they will contiue to have warnings. They just won't be receiving a direct hit from the eye.
South Florida is NOT out of cone, the information you are saying is incorrect the cone will continue to shrink as the center gets closer , and a direct hit is still possible from Miami Dade county on south , that is why a hurricane watch is in effect for miami dade county and the hurricane warning is in effect for the Sw Coast and the keys
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000
WTNT64 KNHC 251525
TCUAT4

TROPICAL STORM ISAAC TROPICAL CYCLONE UPDATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
1130 AM EDT SAT AUG 25 2012

AT 1130 AM EDT...1530 UTC...THE HURRICANE WATCH FOR HAITI HAS BEEN
DISCONTINUED.


$$
FORECASTER BEVEN
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nice and breezy here this morning, suns out real good too..drying up some more today
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Quoting flcanes:

the next 12 hours are crucial to isaac


Well I don't think it's gonna get torn to shreds by Cuba. Should be a cane in a day or two

I would say the Florida strait takes this thing to cat 2

It will tap into the gulf stream no doubt about it.

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Quoting ncstorm:


I am..I havent been able to cut my yard in two weeks..Roanoke, VA received over 11 inches of rain from that wannabe noreaster that tracked over them..the NC, SC and VA will have great impacts from Isaac if this tracks up our way as we are above average in rainfall..grounds are already saturated..a weak TD will push trees over and cause power outages

Just a few hundred miles north of you,we in southern Delaware are about 9inches below avg. for rainfall.I just dont want it all at once.
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Quoting JasonRE:


As of last night, I was uneasy. But this morning as of the latest blog and information provided, I don't think Louisiana has a chance at any part of this storm. I don't even think we'll see rain from it. By the way, here in Lafayette.


Houma here.... We all should know that you never ever take your eye off of any that may get in the gulf....
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328. LBAR
That rainfall forecast looks to be the drought-busting rain the Southeast needs, especially Georgia, South Carolina, and Alabama.
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Quoting CybrTeddy:
Isaac is not going to get ripped apart by going over Cuba for like 6 hours, especially with how strong the model support is for this to intensify. I recall some people this AM making some sort of analogy between this and Ernesto 2006. Ernesto in 2006 did take a similar path though Haiti and Cuba, but by then was already weaker than Isaac when it hit Cuba, smaller, and much less organized plus it was forecasted to curve right into Miami and not get into the Gulf. This on the other hand is stronger, better organized, going to spend less time over Cuba and has very good model support from pretty much all of the models that it will intensify into a hurricane in the Gulf.

(Ernesto 2006)

(Isaac 2012)

Could Isaac weaken further? Probably, I suspect anywhere from 45-50mph when it leaves the coast, with pressures as high as 1002mb or so when recon finds it the next pass. But intensification is likely as Isaac will be moving into very hot waters and is maintaining a decent structure.

jeff said that this could be an analog, a long ts fay
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Quoting JasonRE:


As of last night, I was uneasy. But this morning as of the latest blog and information provided, I don't think Louisiana has a chance at any part of this storm. I don't even think we'll see rain from it. By the way, here in Lafayette.


I disagree and dont count LA out until Isaac is in the straights and models plot off that position and intensity. Remember only a slight deviation results is large changes to the cone. This is a huge storm and even if landfall of the center is in the big bend, the rain bands and winds will be thrown over 200 miles away.
IMO
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This system is too large to be ripped apart right now. But that might be a good thing for people in south florida cause it's gonna take a while to get its act together especially at its current forward motion
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My latest thinking on Isaac.
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Quoting KeyWestwx:
here's a monroe county website to go to for updates http://www.monroecounty-fl.gov/CivicAlerts.aspx?AI D=280 Link

here's a 'snippet' from the site 'The center of Isaac is expected to pass over a point between Marathon and Key West sometime Sunday night. Hurricane force winds are anticipated to be in a relatively small area of the storm. Tropical storm-force winds are expected to extend outward up to 250 miles'
250 miles out..whew when it gets to tampa, daytona will be getting it too wow
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Quoting TomballTXPride:
Spot on, SJ.

?
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Quoting aspectre:
24Aug.12pmGMT: 15.9n70.4w (248.9° WSW @ 8.3knots) 50knots, 1000millibars, TS
24Aug.06pmGMT: 16.7n71.3w (312.8°NWest@11.8knots) 55knots , 995millibars, TS
25Aug.12amGMT: 17.3n72.0w (311.8°NWest@ 9.0knots) 55knots , 992millibars, TS
25Aug.06pmGMT's numbers are below, before 25Aug.12pmGMT's
Derived from NHC_ATCF data for TropicalStormIsaac for 25August12pmGMT
MinimumPressure increased from 991millibars to 998millibars
MaxSusWinds held decreased from 55knots(63mph)102km/h to 50knots(58mph)93km/h
Vector changed from 320.1°NWest@12mph(19.3km/h) to 327.0°NWest@21.9mph(35.3km/h)

DCT-RaggedIsland :: IGA-GreatInagua :: MOA-Moa :: BCA-Baracoa :: JAK-Jacmel :: CBJ-CaboRojo

The southeasternmost dot marks the start of Issac's 4th day as a TropicalStorm
The southeasternmost dot on the longest straight line is TS.Isaac's most recent position

The longest line is a straightline projection through TS.Isaac's 2 most recent positions to its closest approach (within 18miles or 29kilometres) to a coastline
24Aug.6amGMT: TS.Isaac had been headed for passage 13.2miles(21.3kilometres)NNWest of Providencia,Colombia (island off the Nicaraguan east coast)
24Aug.12pmGMT: TS.Isaac had been headed for passage 6.3miles(10.2kilometres)SSEast of Tortuguero,CostaRica
24Aug.6pmGMT: TS.Isaac was had been headed for passage over Cotes-de-Fer, 18miles(29kilometres)South of Miragoane (left, blob left of the straightline projection)
25Aug.12amGMT: TS.Isaac had been for passage over Coates-de-Fer, 18miles(29kilometres)South of Miragoane (right, blob left of the straightline projection)
On 25August between 6:13am and 6:25am GMT, TS.Isaac made landfall on Bainet, Haiti, and was heading for passage over Cajobabo,Cuba (bottom,BCAdumbbell)
On 25August at ~1:50amGMT, TS.Isaac made landfall on Punta de Maisi, and was heading for passage 8.2miles(13.1kilometres)NEast of DuncanTown,RaggedIsland,Bahamas in ~6hours from now (when this was posted)

Copy&paste iga, ger, ccc, moa, bca-20.067n74.461w, 18.175n72.987w-18.182n73.042w, jak, cbj, 16.7n71.3w-17.3n72.0w, 17.3n72.0w-18.1n72.7w, 18.1n72.7w-19.7n73.8w, dct, 18.1n72.7w-22.219n75.586w into the GreatCircleMapper for a larger map and other information
The previous mapping for comparison
i'm going to say it again, this could get ugly quickly
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather