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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I hear ya loud and clear from a page ago GetReal. Anyone who would wish that on themselves must not be able to read. The aftermath is just hell on wheels. A member who went through the heart of Andrew said he/she was without power for six months. Some have posted they found neighbors dead in their garage when they returned. Not to mention skeleton pets who were left to drown or starve. Watching the nightly news last night, some said they had never psychologically recovered from Andrew and will never be the same. Still in awe at how few died in Andrew, that was a miracle.
Member Since: December 31, 1969 Posts: Comments:
Center appears to be emerging off the coast of Cuba. More convection developing on the NE side.
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Quoting oakland:


I'm sitting in Bradenton. Not a laughing matter for me.
I'm on Terra Ceia Bay with a beautiful view of the water...for now.
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1067. dader
Quoting Tazmanian:



reported



...sigh.
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1066. LargoFl
Sarasota County

Ringling College has issued a mandatory evacuation by Sunday for all students. Classes are canceled Monday and Tuesday.
Member Since: December 31, 1969 Posts: Comments:
Isaac will be a Cat.3...if he reach Cat.4 i will be very surprised because the heat content is not to deep
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NO school on Monday, Woot woot.
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Punta De Maisi, GuantanamoElevation
33 ft Report Station You are about to report this weather station for bad data.

Please select the information which is incorrect and click 'Submit' otherwise click 'Cancel'.
Temperature Pressure Wind Forecast Submit — Cancel

Station Select Now
Heavy RainTemperature
76 °F
Feels Like 76 °F Wind(mph)
31 from the SE
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1062. LargoFl
Quoting icmoore:


I don't know yet it's a wait and see... Our area fared better than a lot of places along the Pinellas county beaches with Debby because the canals around us provided drainage from the Gulf at high tide but this is all different and uncertain and so am I right now. I'm not good at the unknown crap. The beaches here took such a beating from Debby I can't imagine how they'll be after this passes.
yeah this could be worse, we'll see
Member Since: December 31, 1969 Posts: Comments:
the gfs 12z has moved back west. the closer to landfall it gets the more likely the models will be correct. i expect to see and westward trend today. with the due west jog he has been on. fingers crossed for a trip over cuba and take the storm apart
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1060. CCkid00
Quoting bohonkweatherman:
Hello Joanie, i use to live in Alexandria, Isaac could go as far west as La. but chances are slim, watch storm and you should be fine. I think this Storm turns North and then Northeast before he gets to La. but that is not 100 percent.


i will keep watching....to make sure Isaac "makes the turn." i remember waiting for Katrina to make the turn. Aug. 26, 2005, 11 a.m., we were not in the cone (east of Baton Rouge) and K was forecasted to hit pretty much where Isaac is now forcasted to hit, in the panhandle. by 5 the same evening, we were then in the cone, but still a panhandle predicted hit. by 11 that night, is when they pretty much had the projected forecast right. Aug. 29, 4 a.m. it hit the La. coast. so...my point is that 3 days out, they missed it by more than 200 miles. everything can change in just a few hours. i think they nailed the forecasted landfall 2 1/2 days out.
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Did anybody look at the forecast verification page on here? It might give you some interesting thoughts...
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1058. peterj
Quoting MiamiHurricanes09:
Awww yeahhh, no classes on Monday for Miami-Dade!!


Opps..I just repeated what you posted.
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1057. QMiami
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1056. oakland
Quoting MiamiHurricanes09:
Awww yeahhh, no classes on Monday for Miami-Dade!!


Wish Manatee County would get smart and do the same thing but nothing yet.
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Quoting stormpetrol:
IMO Isaac is right on the SE Coast of Cuba or slightly inland around 20/75 moving west or just a tad N of due west, just my take, Isaac has slowed significantly since this morning!



naw I think hes over water jmo :)
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1054. Grothar
Quoting Tazmanian:




its all ready been posted your going back words


I was taking a nap and must have missed it. I don't have time to go back and look at all the posts like you do. Next time I will check with you before I post anything so it is not duplicated.
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1053. icmoore
Quoting LargoFl:
IC do you think they will evacuate your area?..i see on the storm surge map..all the beach area's flood


I don't know yet it's a wait and see... Our area fared better than a lot of places along the Pinellas county beaches with Debby because the canals around us provided drainage from the Gulf at high tide but this is all different and uncertain and so am I right now. I'm not good at the unknown crap. The beaches here took such a beating from Debby I can't imagine how they'll be after this passes.
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1052. scott39
Quoting Michfan:


This is why the NHC uses a blend of ALL of them rather than focus on one singular model. No one should focus on one model and say yup thats where its going. You have to take into account all factors when forecasting these things.
Thats my point exactly, yet he continues to say it wont past 85W. NHC has it past that point at landfall.
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i guss will see show stong the storm gets when it enters the open hot gulf waters



and if am right you guys oh me a cookie
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Pardon me if I'm wrong here but, are we trying to say that the gulf has never produced a major hurricane (starting from TS stage) at the current water temps?

I'd have to challenge that assertation.
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1049. miajrz
No school Monday Miami-Dade Public Schools.
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1048. LargoFl
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1047. peterj
School has just been canceled for Miami-Dade for Monday.
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Quoting WXGulfBreeze:


That is a joke.

There are no systems or meteorological wild cards to sweep Isaac that far west. I'm just a lay person, and I can see that. The thing is, there are times that I don't think these guys get fully immersed in the minutiae of storms like this, and simply act as stenographers for the latest doom and gloom scenarios without doing a bit of actual analysis.


Sure there is.

Haven't you looked at the steering?

The previous Euro was close to that scenario anyway, I'm still waiting on the next one.




00z Euro

Look what it did with the steering over the mainland.

It would only take a few miles difference to make the left hook happen over water, and BAM worst case scenario in the nation.

If there's nothing going that way, why do 2 of the top six model consensus BESIDES the Euro go that way, and why does 3 of the old GFS members go that way?


I guess you figure all of that should just be disregarded: The best consensus model plus 3 members of the GFS, plus the GFDL, and NAM should all be thrown out, eh?
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Quoting MiamiHurricanes09:
Awww yeahhh, no classes on Monday for Miami-Dade!!



he's looking good atm I still think uppers keys landfall cat1
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IMO Isaac is right on the SE Coast of Cuba or slightly inland around 20/75 moving west or just a tad N of due west, just my take, Isaac has slowed significantly since this morning!
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Quoting StormHype:


Knock off the BS. 155mph. Get real.



reported
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1042. KEEPEROFTHEGATE (Mod)
at the moment there is the chance
of a C3 storm at the most
but in reality you can never
rule anything out
that would be a fools dimise

watch wait see
the next 24 hrs will tell the tale
and whats to be expected
NHC will send out the word
if it feels a stronger storm
will be the case

always follow NHC advice
in all of the current
storm developement
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1041. scott39
For the most part this blog is biased E. It seems when the GFS runs a more E track it is gold, but when it goes W either it is discounted or not discussed at all. Then all of a sudden when bench player models step to the E.... thier gold and the same scenerio when they go father W. IMO that is not good forecasting...just speculation. To be honest I have know idea wher Isaac is headed, but I do take all model runs into consideration.
Member Since: December 31, 1969 Posts: Comments:
center is back over water now and he;s firing new convection look out!!
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1025 Round of applause.
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Awww yeahhh, no classes on Monday for Miami-Dade!!
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1037. LargoFl
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Quoting Tazmanian:
the mode runs have been pointing at a strong hurricane the ? is how strong will it get be for land fall


am thinking any where from 100mph too 155 mph if things set up this right


Knock off the BS. 155mph. Get real.
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979mb on the gfs could mean strong cat 3 or 4 in real life



or a storm of 990mb on the gfs could mean cat 1 in real life


so you nevere no
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1033. LargoFl
Quoting Grothar:
Just LOOK at the size of this monster
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1032. Grothar
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1031. HrDelta
A reminder. Hurricane Track forecasts have improved in the last 25 years, while intensity forecasts have not.
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1030. oakland
Quoting GTcooliebai:
The thing is though, I wonder if the Doc accounted for the shallower shelf, because I can tell you with my own experience that I went swimming off the coast of Pinellas County which is the next county over from Tampa Bay and it was like bath water, plus wouldn't Isaac be travelling over the loop current if he took the HWRF track?


Some of the water temps near the bay are upper 80s near 90 degrees.
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Quoting Tazmanian:




do you look at mode runs ???
Models is a TOOL, not guaranteed path. Beside, models are saying Category 2 at the best, not Category 4 (except for HWRF).
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1028. Michfan
Quoting scott39:
You think models that have gone father W many times and still presently are(GFS)....carry no weight?


This is why the NHC uses a blend of ALL of them rather than focus on one singular model. No one should focus on one model and say yup thats where its going. You have to take into account all factors when forecasting these things.
Member Since: December 31, 1969 Posts: Comments:
Quoting wunderkidcayman:
hey guys anyone have any obs for Great Inagua Island pleas post it thanks
Check the city search at the top of the page... several observation points along the archipelago.

BTW, folks, we have masses of resources available on the site... take a look through the tabs at the top of the page. Lotta the links u r looking for are right on the tropical wx page...
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Quoting Grothar:
The HWRF still doesn't want to give up





its all ready been posted your going back words
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we are talking about water temper at lest 85+ that is vary right for RI and with light wind shear this storm could really take off
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Quoting Bluestorm5:
Did you read what Dr. Masters said about Gulf? It's not as favorable as 2005 in term of water hear. He doubts a Category 4 or 5.
The thing is though, I wonder if the Doc accounted for the shallower shelf, because I can tell you with my own experience that I went swimming off the coast of Pinellas County which is the next county over from Tampa Bay and it was like bath water, plus wouldn't Isaac be travelling over the loop current if he took the HWRF track?
Member Since: December 31, 1969 Posts: Comments:
Isn't the HWRF notorious for over doing the intensity of storms?
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1021. Grothar
The HWRF still doesn't want to give up

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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