Isaac pounding Haiti and the Dominican Republic with torrential rains

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

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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

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I wonder if they evacuated Scarabeo 9. I bet they don't.
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Quoting Levi32:
12z ECMWF ensembles:



Interesting that a 5-sigma result takes up such an enormous area.

3 sigma is about 99% certainty, but that range goes from as far west as Houma to as far east as S. Carolina for the same time frame.


I guess this makes sense because the "cone" is a 2/3rds certainty...
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Quoting Redbull77:
if it is going west and i say it is going west am i a westcaster.
Another expert I see
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if it is going west and i say it is going west am i a westcaster.
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Quoting stormpetrol:
TRue to goodness , I'm getting sick of this blob, making fun of others just because they have strong convictions about what they're seeing, though it sames farfetched, some are cold and have no feeling for others at all whatsoever , BTW , IMO the center is over land around 20.7N/76.5W Run this Link and watch the wind Observations!



sorry pal 20.7N 76.5W would be impossible GJ trying though
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Quoting cajunkid:
OK, jeez. Just look at this and speed it up

Link
That was cool!
Quoting cajunkid:
OK, jeez. Just look at this and speed it up

Link
That was cool!
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Quoting Civicane49:
Isaac:

Not looking too shabby!
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Quoting stormpetrol:
TRue to goodness , I'm getting sick of this blob, making fun of others just because they have strong convictions about what they're seeing, though it sames farfetched, some are cold and have no feeling for others at all whatsoever , BTW , IMO the center is over land around 20.7N/76.5W Run this Link and watch the wind Observations!


Not seeing what you are seeing. They found the area of lowest pressure 15 miles offshore.
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2159. HRinFM
Quoting Grothar:
The voice of reason.
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Quoting Tazmanian:



for the last time its not overe land it overe the open water at 21N 75W


Good for you Taz, you have your opinion and I have mine! Simple as that Buddy!!
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Quoting Levi32:


They can slip up the west side of Florida, but a track like the 12z GFS from south of Hispaniola NW to the central gulf coast just doesn't show up in the record books.


Maybe Isaac missed History class the day they talked about that lol. Didn't Georges pulled something similar?
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Isaac:

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2155. GetReal


I have always written off the CMC, but it is funny that Isaac is right on top of the last CMC projected track for the last several hours. LOL at the irony.
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Quoting wunderkidcayman:
they can't find the LLC because it's over land duh



I'm going to miss this once Isaac is past the Cayman's longitude... this is too comical.
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Quoting MiamiHurricanes09:
Were you the one that issued a tropical storm watch for the Cayman's yesterday? ;)
I read a post (which is completely wrong!),that Isaac was moving SOUTH WEST and was going directly into the Cayman Islands.People are wasting precious time day and night!!! in this VERY SERIOUS WEATHER BLOG!,putting this type of erroneous information!!!.
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Quoting weatherxtreme:
westcasters out in full today LOL!


As are the eastcasters
Member Since: June 17, 2011 Posts: 11 Comments: 6461
Quoting Methurricanes:
I think it might look kind of wierd for 2 reasons
1) it just emerged from mountaious land
2) it is merging with that cluster of Tstorms currently over Florida.


Ok, thank you for the info!!!
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Quoting Elena85Vet:


Unless I am mistaken, the time on the radar image is either at 0z last night or midnight last night.
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Quoting Hurricanes101:


Recon has confirmed the storm still has 60mph and a pressure of 997mb

the storm has actually fared very well with dealing with land the last 18 hours, looks sometimes can be deceiving


Thanks!!
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Quoting connie1976:
I am watching channel 7 news (south florida) and the storm looks terrible... will it even be a tropical storm when it reaches the keys?
I think it might look kind of wierd for 2 reasons
1) it just emerged from mountaious land
2) it is merging with that cluster of Tstorms currently over Florida.
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2147. Levi32
Quoting floridaboy14:
eastern lousiana to the big bend area. the key will be how much the rebuilding ridge pushes isaac wnw before he starts turning north. your track is nice but mine is just west of yours. is isaac a rare storm or are these type of storms quite common?(ones that cross the Greater antillies into the gulf)


They can slip up the west side of Florida, but a track like the 12z GFS from south of Hispaniola NW to the central gulf coast just doesn't show up in the record books.
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Quoting weatherxtreme:
westcasters out in full today LOL!



Must be talking about the GFS then....It's been westcasting all day....
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2145. Grothar
Quoting connie1976:
I am watching channel 7 news (south florida) and the storm looks terrible... will it even be a tropical storm when it reaches the keys?


It is expected to be at least a Cat 1.
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Quoting stormpetrol:
TRue to goodness , I'm getting sick of this blob, making fun of others just because they have strong convictions about what they're seeing, though it sames farfetched, some are cold and have no feeling for others at all whatsoever , BTW , IMO the center is over land around 20.7N/76.5W Run this Link and watch the wind Observations!



for the last time its not overe land it overe the open water at 21N 75W
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2143. wpb
Quoting wpb:
what needs to be written the land mass is getting closer to sea level he slowly moving away from the 12k mountain into land mass less than 250 ft.
thanks
Member Since: May 28, 2011 Posts: 0 Comments: 572
Quoting Hhunter:
getting a bad feeling about this storm...


Me too. But then again it could of been the egg salad.
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Quoting AtHomeInTX:


Lol. I'm thinking I REALLY should've left the TX out of my handle. :)

LOL
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Quoting STXHurricanes2012:
2043: lmao I know your playing tricks thinking its dead or its alive or etc...the blog doesn't like it!
Love Bon Jovi
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2139. Grothar
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Quoting GetReal:


No RI for the next few hours at a minimum Taz... Look at the loops and you will observe that the south side of the circulation has been choked off by the Cuban mountain range to the south of Isaac.



ok
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TRue to goodness , I'm getting sick of this blob, making fun of others just because they have strong convictions about what they're seeing, though it sames farfetched, some are cold and have no feeling for others at all whatsoever , BTW , IMO the center is over land around 20.7N/76.5W Run this Link and watch the wind Observations!
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Quoting connie1976:
I am watching channel 7 news (south florida) and the storm looks terrible... will it even be a tropical storm when it reaches the keys?


It will at least be a tropical storm if not hurricane.
Member Since: July 7, 2005 Posts: 0 Comments: 5151
Quoting connie1976:
I am watching channel 7 news (south florida) and the storm looks terrible... will it even be a tropical storm when it reaches the keys?


Recon has confirmed the storm still has 60mph and a pressure of 997mb

the storm has actually fared very well with dealing with land the last 18 hours, looks sometimes can be deceiving
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westcasters out in full today LOL!
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2043: lmao I know your playing tricks thinking its dead or its alive or etc...the blog doesn't like it!
Member Since: June 4, 2012 Posts: 0 Comments: 767
Quoting HurrMichaelOrl:
Based on recent model trends, I think it is fairly safe to assume that East Central FL will get intermittent rain showers and a few squalls-basically just some rain. The area may very well experience a few tropical storm force gusts, which happens periodically during rainy season thunderstorms. The Keys may be in for it if Isaac can get its act together, or it may stay weak, just like Ernesto '06. Once it gets into the gulf, however, Apalachicola to New Orleans may be dealing with a hurricane (the first 7 years or so).


What about the Tropical Storm Watches and tornado threat? I think this is a little more serious then intermitten rain and squalls. Otherwise why post watches for a few gusts? There was no TS watches inland for Debby were there?
Member Since: July 7, 2005 Posts: 0 Comments: 5151
I am watching channel 7 news (south florida) and the storm looks terrible... will it even be a tropical storm when it reaches the keys?
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Quoting Maineweatherguy20023:

I love it in Maine. I am never blasted for "wish casting" just sitting up here wondering where it will go. I am free to post my opinion and not get blasted it is really fun!!


Hello everyone, I am just getting on here today and haven't read back thru the pages, it gives me a headache when I do that and I already have one now. Looks like the "wish" casting has come up again. I saw enough of it last night. I would just like to add my two cents. When I see someone who obviously wants to be hit by a storm, I assume they are young, immature, or don't know better. My son is 16, and he wants to experience a storm, despite my telling him how ridiculous he is. It really annoys me he feels that way. I just try to ignore the comments on here and the ones from my son, and figure time will teach. BTW, I am not trying to insult anyone.
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Quoting GetReal:


Isaac is NOT on a good heading that will allow intensification anytime soon. Isaac need to pull away from the N coast of Cuba in order to maintain itself, or to strengthen. If Isaac stays on the current heading, he will stay on the extreme south side of the track cone, and ride up the center length of Cuba.

Which may not be bad for us on the Gulf Coast, if his core is severely damage, or destroyed.


Well it does look like Isaac is pulling away, although slowly.

Plus, looking at a topography map, Isaac is already past the huge mountains of eastern Cuba. The rest of Cuba will be much less of an obstruction for Isaac than Haiti and eastern Cuba have been for him the past 18 hours.



So things are looking up for Isaac.
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Quoting StormDrain:
The underwater topography contributes. Shallower water close to coastline.

image credit: wiki commons
They about to talk about that on TWC good stuff posted.
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Is the center already past Cuba, and if so, isn't that earlier than expected?
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Quoting Maineweatherguy20023:

I love it in Maine. I am never blasted for "wish casting" just sitting up here wondering where it will go. I am free to post my opinion and not get blasted it is really fun!!


Lol. I'm thinking I REALLY should've left the TX out of my handle. :)
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2125. Hhunter
getting a bad feeling about this storm...
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Quoting Realtormama:
Can someone explain why it is supposed to be Cat 2 then fall off to Cat 1 at landfall somewhere in the northern gulf. What makes it fall off?
The underwater topography contributes. Shallower water close to coastline.

image credit: wiki commons
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Quoting HurrMichaelOrl:
Based on recent model trends, I think it is fairly safe to assume that East Central FL will get intermittent rain showers and a few squalls-basically just some rain. The area may very well experience a few tropical storm force gusts, which happens periodically during rainy season thunderstorms. The Keys may be in for it if Isaac can get its act together, or it may stay weak, just like Ernesto '06. Once it gets into the gulf, however, Apalachicola to New Orleans may be dealing with a hurricane (the first 7 years or so).


Isaac is very large, you will likely get TS conditions
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Quoting RTSplayer:
Quoting cajunkid:
COC opening up now. Not as tight as earlier.


What are you looking at man?

This is the best radar presentation the core has ever had, though we can't say much for when it was S of Haiti since there was no radar, but wtf...

This thing is re-building an eye-wall and probably about to go RI...

Strengthening is NOT going to happen rapidly anytime real soon. Isaac not the well organized and it is near (too close) or over land. Everyone knows you are anxious for RI!!!!
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Quoting GetReal:


No RI for the next few hours at a minimum Taz... Look at the loops and you will observe that the south side of the circulation has been choked off by the Cuban mountain range to the south of Isaac.




ok
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.