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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48 hours


Going right?
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Quoting chrisdscane:



you still seeing the northward jog or did it stop??
Yep; looks like a NNW movement right now. As soon as Recon gets in there we'll have confirmation, but I firmly believe that the center is over water, or on the coast.
Member Since: December 31, 1969 Posts: Comments:
not sure is the recon is at the center yet but they have found

999.5 mb
(~ 29.52 inHg
Member Since: December 31, 1969 Posts: Comments:
Quoting MiamiHurricanes09:
More intense than the 06z run, and that had a major hurricane in the northeastern Gulf coast. May warrant some hurricane warnings for the southeastern Florida coast should models trend this way this evening.



and with this north jog they might have too
Member Since: December 31, 1969 Posts: Comments:
40% chance of reaching Cat2+ according to Jeff; love when he disagrees with the NHC. NHC always play it close to the vest with intensities, they really hate overdoing a storm. Anyone with an update on how bad it's been for the Haitians so far? Wonder if 97L is going to shape up to be the first major in the Atlantic basin this year, starting to look like a possibility.
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Quoting MiamiHurricanes09 [#849]:
More intense than the 06z run, and that had a major hurricane in the northeastern Gulf coast. May warrant some hurricane warnings for the southeastern Florida coast should models trend this way this evening.

So that'd be a Cat 2 over Naples. Hmmm...
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ok guys what I think is that we have weak elongated LLC or multiple LLC and a kinda weak MLC

the multi or elongated LLC are over cuba and the MLC is on the Northern SE tip coast I still think that the main weak LLC is on the southern half of the SE tip of cuba wind obs from cuba does show this and radar show N half of the tip what ever is there moving W and South half hardly show much but the few speck that are there are moving E so circulation is weak but its over cuba
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Quoting tennisgirl08:


No, Taz! You are hyping.
Please don't forget to included the oil rigs in the open water gulf
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...look at all those warnings
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One thing I haven't seen anyone discuss - when Isaac arrives, we're going to be close to a full moon. If he comes in around Mobile / Pensacola, the full moon will definitely increase storm surge potential in both Mobile and Pensacola Bays (as well as all bays / sounds from Mobile east to probably Panama City Beach).
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GetReal which model is that?
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Quoting tennisgirl08:


No, Taz! You are hyping.




this wait and see when this gets in too the open gulf then will see oh is hyping
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How can anybody discount Isaac going W of the panhandle? The GFS currently and the Euro for many runs before last night has also. To say it will not go father W on the Gulf Coast is ill advised.
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Quoting GTcooliebai:
Yeah that Ridge is strong, I'm thinking it comes down to the orientation of the Ridge if it's south to the north then the more eastern trajectory of the cone it takes, if it's nosed in then it forces it more on that NW path towards the Gulf Coast.


It's going to be a tough call, and the models are still struggling quite a bit. We might not have a good handle on Isaac until tomorrow.
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Quoting Grothar:
It did take a "jog" North, but that was expected.


It's pretty much wnw again
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Quoting Tazmanian:
i think we could be looking at a strong cat 4 or low cat 5 some where in the gulf then some sight weaking be for land fall too a strong cat 3 with cat 4 or 5 waves


No, Taz! You are hyping.
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Quoting TropicalAnalystwx13:
My forecast...pretty much unchanged from two days ago in terms of final landfall position and intensity.

wx13.......I agree.. You might want to but an intensity over Key West....But very good
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Quoting GetReal:
42 hours
see how close he is to the coast
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Quoting GTcooliebai:
hmm???



Makes perfect sense cause of the NW movement the storm has been o for a while.. A Miami hit is not out of the possibility. It would be the first time Miami directly got hit with a Hurricane since Katrina in 2005.
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After Debby, I don't put much stock in the NHC's Winds graphic. They showed much of the bay and surrounding area with a 100% chance of TS force winds, but there weren't any.
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Quoting MiamiHurricanes09:
SEFL landfall in 36 hours. Minimal category 1-ish.

Image in post below:



you still seeing the northward jog or did it stop??
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More intense than the 06z run, and that had a major hurricane in the northeastern Gulf coast. May warrant some hurricane warnings for the southeastern Florida coast should models trend this way this evening.

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Quoting GetReal:
36 hours


The models are flip flopping so bad it's like the GFS and the HWRF are playing musical chairs right now. We can't rule out a solid hurricane in Miami or even New Orleans and this point. The models or really struggling with Isaac.


It's funny, and here I thought that forecast would be pretty straight forward by today as of Thursday days ago, so much for that lol.
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Quoting Jedkins01:



Alright, I don't really remember the cone that well, and I didn't feel like digging out of archives, so you got me, lol.

Anyways though, I agree about the cone issue. I can also see why the NHC uses the center piece of the cone as well. Maybe it would be better to use the black center line in the cone only for meteorologists for symmetry, and for a consensus point, and just remove the black line for the general public because despite how many times people are noted not to focus on the center line, many of them do.

Just go to the link below, and you'll see that both Punta Gorda and Tampa were in the cone and very near the "look at but don't use" centerline for two days before Charley made landfall:

http://www.nhc.noaa.gov/archive/2004/CHARLEY_grap hics.shtml
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42 hours
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Quoting MiamiHurricanes09:
If the circulation is really emerging off of the coast already, I can't see why that wouldn't be a plausible solution. Interested to see if the 18z model plots react should the circulation be more poleward than originally anticipated.


Will be interesting. Like Levi said a couple days ago, the big variable is how Isaac reacts to the terrain of Haiti and Cuba. It seems to have done well with Haiti and look to be trying to jog out back N over water from the tip of NE cuba already.
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It did take a "jog" North, but that was expected.
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Quoting PunchDaddySeasoning:
Taz

What is the chance that this storm takes the Katrina path? Should we start looking at prep. for this storm?



right now thw nhc has this storm E of where Katrina made land fall but i would prep this in case
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hmm???

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Quoting EastCoastMove:


I am with Levi, no way that it makes it that far west. I would shift a bit east into panama city. I am sticking with that prediction.


From your keyboard to God's monitor.
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Quoting CaneHunter031472:


Katrina was awful. I got lost trying to get to my home, because every single landmark was substituted by rubble. I am grateful to God because we left the area before it hit and the whole entire family made it well, but Rebuilding can be a very traumatic experience. Thank you for your prayers, and I think your advise is wise I will start moving a few things and keep an eye on things. This will be a sleepless weekend. I just hope it dissipates I do not wish this on no one and wishing it moves to the east makes me feel like an awful person, so I will wish it dissipates.


Yes I agree that it would be good for the storm to weaken. This isn't a game or something to laugh about. This is a serious storm with potential to threaten plenty of lives and property. This is the worst thing to being a weather forecaster. We here at the blog can be wrong and no harm done except one's ego but the forecasters at NOAA and other forecast places get crap from the public (including this blog) but in the end they are the ones that have to make the life and death decision. That isn't something I would look forward to. I agree that sometimes I am critical of NOAA but at least I don't have to tell people when to move and then take the heat when I don't tell others to move and they lose their lives or property in the storm.
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i think we could be looking at a strong cat 4 or low cat 5 some where in the gulf then some sight weaking be for land fall too a strong cat 3 with cat 4 or 5 waves
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SEFL landfall in 36 hours. Minimal category 1-ish.

Image in post below:
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36 hours
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834. MahFL
Convection is already increasing on the NE part of the coc.
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Quoting caneswatch:


WPTV showed about 24 hours worth of TS force winds for South Florida.


Maybe more.
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Quoting TropicalAnalystwx13:
My forecast...pretty much unchanged from two days ago.



I am with Levi, no way that it makes it that far west. I would shift a bit east into panama city. I am sticking with that prediction.
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Taz

What is the chance that this storm takes the Katrina path? Should we start looking at prep. for this storm?
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I am in Central LA, The weatherman here doesn't think we will have anything to worry about with this storm...but me, being a weather fanatic, I am still a little weary..remember Rita? It was suppose to go to the central coast of Texas and it kept creeping more up the coast to LA??...well my gut feeling tells me to just keep watching cause no one REALLY knows where it is going...NOONE...any thoughts???? TIA:)

Joanie :)
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Quoting TomballTXPride:

That model is notorious for a poleward bias.
Not really; it's been pretty stagnant amongst the consensus the past few days for a central Keys landfall -- this is the first time that it looks like it's headed for the northern Keys, southern Florida mainland.
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Quoting tennisgirl08:


Yeah, not looking good for where you are right now.

Stay alert!


We're good to go. Organized the shutters yesterday and gassed up the vehicles; braved the crowds at Wally World very early today to pack in a few more provisions.

Here's the kicker - spouse works in Birmingham three days a week (Mon - Wed), and it looks like they could get an extended soaking, too.
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I think the upper low to the NW of Isaac is making him take these northerly jogs. Also, storms always seem to jog around land.

I think this is temporary, though, and he will resume his NW motion and follow the NHC trajectory.
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Quoting HurricaneDean07:

If NHC is predicting 100 Mph now...
You should expect borderline 2/3 at landfall... Very BIG situation.


The Northern Gulf will not sustain that strength unless it makes a strong cat 3 well before landfall. The storm will be a cat one borderline cat two at landfall.
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Quoting TropicalAnalystwx13:
My forecast...pretty much unchanged from two days ago.


I agree
Member Since: December 31, 1969 Posts: Comments:
Like Levi has stated before sometimes these storms will wobble from the land interaction with Haiti and Cuba and this always throws a curveball into the entire track. Storms tend to want to be over water rather than land so they tend to push off because of this. Doesn't look like Cuba is going to interact with the center of Isaac much which gives it more time to strengthen over the north coast of Cuba now.
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Quoting Jedkins01:



I'm sticking with a similar path to his, I'm not sure where you're getting the weak ridge from, but regardless I don't buy it going as far west as some of the models. I really doubt the Tampa Bay area will see a direct hit though at least. The trajectory of land doesn't support that unless Isaac pulls another Charley, but obviously that has to be discounted always in a forecast.
Yeah that Ridge is strong, I'm thinking it comes down to the orientation of the Ridge if it's south to the north then the more eastern trajectory of the cone it takes, if it's nosed in then it forces it more on that NW path towards the Gulf Coast.
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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