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 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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Once again the models are trending west toward the EMCWF, the top ranked model.
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Quoting Levi32:


That's a short-term northerly outlier now compared to the other 12z models.

consensus is fairly tight
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Quoting HurricaneHunterJoe:


I could not get into Cuban site for their radar. Do you have a link for Guantanamo Radar?


Link
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Quoting GetReal:


HWRF starting to run also.


At least it is in the proper position!
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30 hours


finally coming west into Fl Straits...
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Why do the models keep shifting back and forth on the Gulf Coast and it seems to be the same locations each time.
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Quoting Grothar:


I am more concerned with Tornadic activity in Dade and Broward. I think we will see near to TS force winds for a long time. Should be a lot of coastal flooding.


WPTV showed about 24 hours worth of TS force winds for South Florida.
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My forecast...pretty much unchanged from two days ago in terms of final landfall position and intensity.

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According to Bay News 9 chief meteorologist Mike Clay, there are already reports in the Keys of 50- to 60-mph gusts.

"That's associated with an upper-level low," Clay said. "That's the weakness we've been talking about for about four days. The tropical system is going to follow the upper-level low, and once it gets to Florida, it should begin to have less wind shear and an environment more favorable to strengthening."

Computer models that plot the chances for high winds indicates that the Bay area has a 50 to 60 percent chance of getting tropical force winds Sunday going into Monday, Clay said.
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Quoting KEEPEROFTHEGATE:


Be careful KOTG. People see that 155 and think MPH not KMH….lol!
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Quoting Levi32:
Isaac's center does appear to be nearing the northern coast of Cuba already. Right now visible satellite is a better tracking device than the primitive Guantanamo Bay radar.

Rapid-scan Visible Loop


I could not get into Cuban site for their radar. Do you have a link for Guantanamo Radar?
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Quoting scott39:
Again!!


Exactly where I don't want him to be. I'd rather his center come right over my house. Drat.
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Quoting Levi32:


That's a short-term northerly outlier now compared to the other 12z models.
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.
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Quoting seflagamma:


Grothar, we are wet here on Broward! Seems like the storm started hitting us last night..
oh I forgot , it did! Lo)


Wonder how bad our winds will get Sunday afternoon with the storm off Key West???


I am more concerned with Tornadic activity in Dade and Broward. I think we will see near to TS force winds for a long time. Should be a lot of coastal flooding.
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Quoting GetReal:
12 hours

Highballing slightly id say 989 or 990
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Quoting MAweatherboy1:
It's far from over in Haiti... Actually, it's barely started, most of the rain is on the back side of the storm:



Yikes. Kind of reminds me of Hanna in 2008. Kinda meandered north of Haiti dumping tons of rain.

Seems like every season Haiti gets hammered.
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Quoting yoboi:


how low did wilma get???


882 officially.

Which is like 100mb lower than a category 1/2 borderline storm.
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Quoting Tazmanian:
recon this took off


Unfortunately is going to take a while since is going out from St. Croix... so about 1hr +/- 10min or so.
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Quoting HurricaneDean07:

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


yea and keep in mind they are always conservative. If they say 100 MPH then expect something worse. I don't think they have hit the full panic button yet. That probably is coming once he reaches the gulf.
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Quoting GetReal:
24 hours


That's a short-term northerly outlier now compared to the other 12z models.
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Quoting WXGulfBreeze:


That's showing Isaac coming right up Mobile Bay.
Again!!
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Quoting Tazmanian:
recon this took off
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Quoting MiamiHurricanes09:
First time that I get a real good look at the surface circulation: Link.

Correct me if I'm wrong, but am I the only one that is seeing the circulation move from Imias, Cuba in in the southeastern tip, and jog due north to near Baracoa, Cuba, on the northeastern tip over the past 90 minutes? If you speed up the loop sufficiently, you'll see a tight surface circulation executing that motion. Thoughts?

Looks like the center is over water.
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Quoting Maineweatherguy20023:

Katrinia was 902 and isaac is NOT going down to 918...


You hope...
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Quoting weatherbro:


Actually the models keep the ridge fairly weak. They must be seeing something else steering it that far west. I'm with Levi on a more eastern scenario.



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.
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793. DVG
http://www.keywestwebcamlive.com/


Smathers Beach nice cam w audio
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Quoting GetReal:
24 hours
North. Very north actually.
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Quoting GetReal:




Looks further west than Mobile?? Just saying???


That's showing Isaac coming right up Mobile Bay.
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Quoting MiamiHurricanes09:
I wish I could show you exactly what I'm seeing, but right around the time the advisory was initiated, the circulation seemed to be coming onshore at WNW heading (which the coordinates, as well as the discussion reflected), but if you continue to monitor that same circulation, you can see it heading due north over the past 90 minutes, basically emerging off of the northeastern coast as we speak.


I see exactly what you're talking about so you're not alone
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Vis shows a bit of a N jog to try and stay over water on the NE Cuban coast.
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It's far from over in Haiti... Actually, it's barely started, most of the rain is on the back side of the storm:

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I am in Ft.Lauderdale...am I the only person that has noticed that this is STILL just a tropical storm,and it could fall apart once it starts scraping the top of Cuba, or hits their high mountains? Everyone,everyplace that has anything to do with this storm,has it almost as bad as Hurricane David already!

I just saw on Ch. 10 weather, a 'wind possibility' map for south Fla. Rating from Low to High the possibility of getting hit by high winds,and it is still tropical storm speeds, NOT hurricane, Miami has a high chance of getting the high winds, BUT Broward,where Ft.Laud. and I are, had a Low risk of getting any high winds! I hope!!! Why dont they predict or show us maps of the winds,instead of making everyone in the country think this is already Hurricane David reborn? It is still a tropical storm, and COULD fall apart...couldnt it? Or be pushed down into Cuba by that high pressure that has been keeping it to the south for so long.

I know it isnt as exciting as hearing south Fla. will be wiped off the map again..but what happened to the chance of this going into Cuba,into the gulf and hitting the Yucatan,or falling apart on its way to the Keyes?
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Isaac departing Cuba.
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Quoting mynameispaul:


Remember also that insects and snakes kinda go bazonkers after the storm passes. Wasps will sting you for no apparent reason and snakes are more brave around people.
indeed, please be very careful with all the wildlife we have here in florida
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Quoting WXGulfBreeze:


I hope so. I absolutely don't want to be on the east quadrant of Isaac at landfall. Just FYI, I am located just east of Pensacola.


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

Stay alert!
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I didn't think this thing had a chance to make the 77-22 doorway yesterday, but here Isaac is stumbling, bumbling around and he just might fall through it.

I'm beginning to see that Levi's original track may come back in to being, it just depends on how deep that subT digs in between these highs.
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recon this took off
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Quoting Levi32:
Isaac's center does appear to be nearing the northern coast of Cuba already. Right now visible satellite is a better tracking device than the primitive Guantanamo Bay radar.

Rapid-scan Visible Loop



do you think he jogged north?
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24 hours
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This will be a LA/MS storm. Very close to the K storm track. Alittle weaker but alot more water. LA/ MS people need to keep a close eye on this one. Moving very slow when it reaches land also. Just my thought
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...Alright so at least I know I'm not the only one that saw that take place hahaa.

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776. wpb
Quoting tennisgirl08:


I see what you're talking about. But I am not sure that is the exact center. His center is so broad that it is hard to tell. I think he's still over the coast of NEastern Cuba - moving W/NW.
over ne cuba moving along the coast
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Yeah I have to go with Levi here. Living in SE GA, I can't count the number of times the track of a CV storm has started in FL, and then as it gets closer and closer, starts sweeping up the coast, eventually getting to SAV, and then continuing on past, to Charleston, Myrtle Beach, and then OBX. It just baffles me that this time, its going the opposite way, EVEN THOUGH the storm is getting stronger from run to run, which should imply more poleward movement, rather than less.
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Quoting etxwx:
A reminder for folks new to coastal and inland areas


Remember also that insects and snakes kinda go bazonkers after the storm passes. Wasps will sting you for no apparent reason and snakes are more brave around people.
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Quoting Walshy:

Link

3 Killed
I unfortunately expect that to rise.Isaac has been dumping copious amounts of rain on the entire island.
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Quoting WXGulfBreeze:


Outliers. The model clusters are between Mobile, Al. and Panama City, Fl. Latest NHC model is showing Cat 2 at landfall. La. / Ms. is on the far west side of the cone. Could it shift further west? I really don't think so. There are no - I repeat, no - meteorological wild cards that could punch Isaac much further west than Mobile.





Looks further west than Mobile?? Just saying???
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Quoting Chiggy:
GFDL, CMC and now GFS moved WEST of 87.5W, If 12Z EURO shows something similar then NHC probably has no choice BUT to move the cone WEST....


Yep. But it will then move back east again...and so forth....haha!

At some point, the models have to quit flip flopping.
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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