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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HWRF visually shows my forecast but about 50 miles to the west and ending in KTLH.
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Quoting GetReal:
54 hours


Into Tampa like many on here are looking for... Be careful for what you wish for...
Could we please cool it with verbage like "what you wish for" That's insulting and insinuating people want death and destruction. People are discussing model track and Jeff has even called for a 40% chance of cat.2+. No one "wishes" for this, we watch in awe and are intrigued by the possibilities.
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Geesh. Can we get a consensus on the models already instead of all this flip flopping.

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Quoting GetReal:
60 hours


DOOM!


yeah... that would SUCK
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am really thankful for this great breeze..feels really nice outside
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This will keep the blog going next week. This is the one to really watch. I saw it first.

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Its been made very clear that the intensity of a TC can change quickly. It is hard to forecast, and technology will catch up eventually.
Member Since: December 31, 1969 Posts: Comments:
Quoting WxGeekVA:


right this also agrees with me
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Quoting mobilebayrat:
Went to the store this morning early. Was suprised at the number of people in there at 7:30. Pretty much every cart had a case of water in it and the lady checking out in front of me commented that the shelves were empty when she got back there. folks were picking up batteries too. Was nice to see that people are paying attention and preparing here on the Alabama gulf coast!


Hey Mobilebayrat! I'm here in Mobile as well. Wife and I went to walmart last night and it was the same situation. Also, I stopped to fill up my truck on the way home from work yesterday and there were already lines 2 deep at each of the 16 pumps.
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Quoting GetReal:
66 hours



Never seen a system bomb that clse to the coast in NE GOM>>>




oh boy
Member Since: December 31, 1969 Posts: Comments:
Did Isaac cross Cuba yet?
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Quoting GetReal:
54 hours


Into Tampalike many on here are looking for... Be careful for what you wish for...


If they are wishing for it they must not have their homes and lives on the line. I would suggest they go watch a disaster movie and get it out of their system.
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There seems to be a fly in the ointment, that is, a surface low near the Cayman Islands seems to be interacting with Issac. That same low is also causing an area of showers/t-storms ftom S Florida to Central and West-Central Cuba. This is one variable which may yet alter Issac's projected path somewhat.
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66 hours



Never seen a system bomb that clse to the coast in NE GOM>>>
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Quoting CybrTeddy:
HWRF is portraying a very powerful hurricane off Tampa by 50 miles by 60 hours into the run. Because of this, the system is more pole-ward influenced. Rather crappy situation for Tampa, but I am willing to bet it is overdone some.


I agree, the intensity is probably overdone, but the track is good.
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WOAH. HWRF out to lunch. major hitting tampa. too far east and too strong
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That's what I see Miamihurricane09, which looks to be good news because it looks from that short clip it very well will run back into Cuba.Maybe if it gets close enough to the spin south of Cuba it will bring back Wkidcaman.
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Member Since: December 31, 1969 Posts: Comments:
Quoting tennisgirl08:


The HWRF is way off here. Too strong and too far east.


Not too far east, a stronger storm moves more north into the weakness instead of busting into a developing ridge as some of the models show. HWRF (track wise) makes alot of sense.
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HWRF is portraying a very powerful hurricane off Tampa by 50 miles by 60 hours into the run. Because of this, the system is more pole-ward influenced. Rather crappy situation for Tampa, but I am willing to bet it is overdone some.
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Quoting TropicalAnalystwx13:

It takes it too far north in the short term.
It has it near 22N in about 12 hours, and it initialized the circulation at the latitude where I believe it is right now. We'll see what it does; the mean motion is NW, if it has more N-ward wobbles than W-ward wobbles, a track that poleward could verify, especially since I believe it's moving NNW-ward right now based on latest satellite imagery.
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Quoting GetReal:
54 hours


Into Tampalike many on here are looking for... Be careful for what you wish for...



lol I'm not wishing for that I'll tell you right now, I live pretty close to Tampa Bay in Pinellas and my elevation is only 4 to 6 ft, a 100 mph hurricane for example would put my house under at least 5 ft of water, it's that bad of a risk zone where I live. Furthermore, wind speeds are always much strong here in Pinellas County during many tropical cyclone events than surrounding areas because we are a miniature peninsula and we stick out farther towards the gulf.


Admittedly, it would be very fun to see the storm get close enough to give us tropical storm force winds and heavy rain, that way I still see some action without significant problems. I'm sure you probably feel the same way, lol.
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Quoting WXGulfBreeze:
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).


Someone did mention this a few days ago. It is a valid point. Surge will be exacerbated by the tide.
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Quoting Mamasteph:
yeah..I hope someone tells Issac he's not allowed to cross from Volusia to Flagler..lol..warnings stop at Flagler beach..at least for today..lol of course I'm 2 miles north of Flagler beach..and 10 miles inland...
warnings might go northward tonight or early tomorrow, stay safe over there ok
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Quoting TropicalAnalystwx13:

I had 12 hours increments at first, but when I added the intensity text boxes, the image as a whole was really cluttered so I resorted back to 24 hour increments. For anybody that is interested, I think it will pass through the Keys as a 75-80 mph hurricane.
Thanks wx13
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Quoting bigeasystormcaster:

The heat content in the eastern gulf will not support that strong of a storm. Cat 2 at most!


whatever thats ridiculous....GORDON if you remember maintained 110mph winds in 73-76 degree water temps...81-86 will suffice for a cat 3 or stronger, plus its not only the water temps that make the storm grow. other factors will inhibit strengthening, NOT the water temps!
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Quoting Tazmanian:




this storm can be come a cat 5 look how big the W PAC storms and they can be come strong cat 4 and 5 storms no matter how you look at small storms and big storms can be come vary powerfull


IMO, Isaac would really have to wrap up and get his act together to be a Cat 4 or 5. I'm not saying it's impossible; just highly unlikely.
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Quoting scott39:
Fl. is the main topic of disscusion right now. By Monday we could be talking about that, and yes it would not be good.
I was wondering about that myself. Good point.
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Ouch, so much for every cruising on my parents boat again if HWRF comes true. I kind of doubt it will intensify that much, the land will be at least a little drag on the circulation right?
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Quoting GetReal:
54 hours


Into Tampa like many on here are looking for... Be careful for what you wish for...


The everglades won't weaken the storm like most landmasses do.. It's possible it stays a Hurricane throughout that track across Florida.
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Quoting tennisgirl08:


But, seriously, he will not be a Cat 4 or 5. That is just plain hyping.

I don't doubt this could be a serious situation, just not a CAT5 doom scenario.



yes it will am thinking strong cat 3 low cat 4 storm at 2nd land fall and am not hyping
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Quoting GetReal:
60 hours


DOOM!


The HWRF is way off here. Too strong and too far east.
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Quoting GetReal:
60 hours


DOOM!
Cat 3 right into Tampa.Worst case scenario.
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Went to the store this morning early. Was suprised at the number of people in there at 7:30. Pretty much every cart had a case of water in it and the lady checking out in front of me commented that the shelves were empty when she got back there. folks were picking up batteries too. Was nice to see that people are paying attention and preparing here on the Alabama gulf coast!
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Member Since: December 31, 1969 Posts: Comments:
You can use this to double-check whether the plane is actually in the storm:

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Quoting weatherh98:


Yes I know. I was stating the obvious :)

G=6.67 x e-11 m2/kg2


I didn't you you spoke "Math" LOL
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Quoting bigeasystormcaster:

The heat content in the eastern gulf will not support that strong of a storm. Cat 2 at most!


I agree. Cat 4/5... LMAO. Silly.
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933. drj27
TWC is a joke i mean im no weatherman but the guy just said the gfs has it going to nola/ms im in ft.walton beach im prepared i hope everyone else is
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Quoting LargoFl:
....SEE..issac has a 1 in 3 chance to be OUTSIDE the cone


Yes, I've repeatedly told people that, and few seem to listen.

It's statistics, so it's roughly 16.5% either way on average, but it varies slightly for each forecast cone, because the statistical maximum is not necessarily the physical center of all theoretical possibilities.
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Quoting KEEPEROFTHEGATE:



always expect the unexpected

isaac is not a joke
and will be far from
a laughing matter


But, seriously, he will not be a Cat 4 or 5. That is just plain hyping.

I don't doubt this could be a serious situation, just not a CAT5 doom scenario.
Member Since: December 31, 1969 Posts: Comments:
From local weatherman:

"Just got off a conference call with south Florida Mets and nws staff. We are on the same page for palm beach and Treasure Coast. 40-50mph with stronger gusts and 5-10" of rain. Winds pick up Sunday afternoon"
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Quoting MiamiHurricanes09:
12z HWRF falls right in line with Levi's idealism. A leftward track scraping along the western Florida coast.

It takes it too far north in the short term.
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60 hours


DOOM!
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Quoting Tazmanian:




this storm can be come a cat 5 look how big the W PAC storms and they can be come strong cat 4 and 5 storms no matter how you look at small storms and big storms can be come vary powerfull

The W PAC storms have DAYS and DAYS over hot water to strengthen not maybe 2 days. also they havnt been ripped to near shreds by 10000 foot mountains.
Member Since: December 31, 1969 Posts: Comments:
Quoting MiamiHurricanes09:
12z HWRF falls right in line with Levi's idealism. A leftward track scraping along the western Florida coast.
If that is the case then no one should take their eyes of this especially if they are in the NHC cone.
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Good and bad news out of Haiti. Only three have been confirmed killed at this point. Bad news is virtually no one left the camps and hundreds of tents have been felled by trees and rushing water. Emergency management is going through the camps currently looking for more victims.
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Quoting GetReal:
54 hours


Into Tampa like many on here are looking for... Be careful for what you wish for...



looks like strong cat 3 there
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Member Since: Posts: Comments:
Quoting GetReal:
54 hours


Into Tampalike many on here are looking for... Be careful for what you wish for...


NO THANK YOU!
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Quoting wunderkidcayman:
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


I have to agree with you here, WKC. Although, I don't think its moving W and South, but W/NW.

The circulation is so broad it is really hard to tell. I think he might still be over Cuba though but on the Northern part of Cuba.
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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