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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recon found winds of 55mph, I think they will keep the intensity at 60mph
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Quoting STXHurricanes2012:

sykkid is troll the more I see it! Saying this storm is done which it isn't!!!


Can you stop policing the blog please...

cr*p spelt as it was, is not a swear word.

and sykkid did NOT say the storm was dead.

Isaac will hit cane status by 1pm UTC Sunday i think
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2018. Levi32
Quoting Hurricanes101:


thats my thought, plus, just as many of the major models shifted eastward, then did shift west; actually if you take out the Bamm suite, more shifted east then west


BAM suite is initialized off of the previous GFS run anyway, so where the GFS goes, they generally go.
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2017. wn1995
Quoting Civicane49:


That is a good view... looks like it is finally JUST offshore.
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Quoting GeauxGirl:


That's what I see too. I was about to breathe a sigh of relief, and then GFS pulled a "psyche!". Could you explain the trough and what's pulling this thing westward?


High pressure is building in from the north and east causing Isaac to move on a WNW motion currently. Friction with Cuba could also be helping to keep it closer to shore. The speed of Isaac and the trough coming from the Western US will ultimately determine where he begins to curve north into the Gulf Coast. Strength of Isaac will probably play a bit of a role as well. HWRF bombs Isaac into a 945mb hurricane on the West Coast of FL and thus he makes landfall in the Big Bend. I see that as unrealistic at this point.
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Center appears to be about 20-30 miles north of Cuba at this time.
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Quoting MiamiHurricanes09:
There we go, that's a lot better. Thanks Cybr/Drak.


21n 75w u agree?
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recon found 997.7mb


997.7 mb
(~ 29.46 inHg)
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Quoting Seflhurricane:
Looking at all the recon info thus far winds have not been above 50 Mph based on what i have seen
thats because they can not sample all the storm, the center is too close to Cuba
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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?
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Quoting LouisianaWoman:
New Iberia, LA here. I'm worried, but not for myself. I'm paying close attention for my family in Chalmette. They're too close to uncertainty right now for me to breath a sigh of relief. I remember how Katrina kept shifting further and further west with each advisory, until they were essentially in the crosshairs. Seems like we'll have a day or two to figure out if they're coming over for a visit.


Nola here - definitely watching. Prepared but watching. To add to the worry, both of my sons are in Pensacola, plus three grandbabies and my mother. Sister in Pascagoula. Weekend house in Gautier. Magic 8-ball says I'm going to be working my butt off in the heat next week no matter where it hits.
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COC opening up now. Not as tight as earlier.
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Quoting Tazmanian:




yup take in at 21N 75W


thats were "my" next forecast piont is lol
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I see some models jumped west....dunno how far west isaac would track in gulf...im thinkin somewherre from mobile to apalachicola myself
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Quoting Methurricanes:
I would say slightly eastward ajustment, it came of cuba early, giving it more time to strengthen, and be pulled north earlier


thats my thought, plus, just as many of the major models shifted eastward, then did shift west; actually if you take out the Bamm suite, more shifted east then west
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Quoting Levi32:


They are trying hard. 998mb is the new extrapolated pressure minimum.

Looking at all the recon info thus far winds have not been above 50 Mph based on what i have seen
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I would say slightly eastward ajustment, it came of cuba early, giving it more time to strengthen, and be pulled north earlier
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Quoting CybrTeddy:
This satellite image that Drak posted is very, very helpful on determining where the center is going as it automatically tracks the center to keep it exactly in frame. Heading WNW at this time, away from Cuba. On track per NHC.
Link


Very nice link. You can really tell his movement in that one. Right in line with NHC.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
Quoting CybrTeddy:
This satellite image that Drak posted is very, very helpful on determining where the center is going as it automatically tracks the center to keep it exactly in frame. Heading WNW at this time, away from Cuba. On track per NHC.
Link
There we go, that's a lot better. Thanks Cybr/Drak.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting TropicalAnalystwx13:

No, they don't. The center is just offshore.


I agree the center is now offshore with the center at 21.5N 75.6W moving NW
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Levi, Drak or Mississippi.. should that convection around the Bahamas have any affect on steering Isaac?
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Quoting CybrTeddy:
Calling someone a wishcaster should be worthy of a ban on here. I never use it, same with downcaster. Causes too much drama in a place where drama shouldn't exist. The people who call the entire blog a load of wishcasters should honestly get off their high horse and actually attempt to listen to what we're talking about instead of generalizing. Same with people who call people downcasters.


You forgot about Floridacasters.
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1997. ITCZ
Link



Statement from Neil Armstrong's Family. I know he isn't Isaac news, but he is an inspiration and showed great courage. A moment of silence for mankind is appropriate, I think.
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Quoting TropicalAnalystwx13:
998.1 millibar pressure.




yup take in at 21N 75W
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Quoting WeatherNerdPR:

Looks like it's offshore to me...

Yep!
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I'm seeing that the track models are trending west moving Isaac away from Tampa but anyway I'm prepared for whatever Isaac could bring to Tampa Bay Area. The question is if Isaac is going to get stronger and amplify the wind field so it can cover more area. We'll see.
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Quoting Drakoen:


Did you look at my link and not the one Levi posted?
Only the one Levi posted. I'm searching for your link now.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Caner:
That Low over Cuba to the NW of Isaac is beginning to look better in its own right...

A Fujiwhara effect in the gulf would be photogenic...


This is what I was asking about earlier. Isaac is about to interact with it.

Levi any thoughts on this?
Member Since: July 17, 2008 Posts: 0 Comments: 1242
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This satellite image that Drak posted is very, very helpful on determining where the center is going as it automatically tracks the center to keep it exactly in frame. Heading WNW at this time, away from Cuba. On track per NHC.
Link
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Gonna be interesting to see where nhc puts the next track, maybe a slight shift west towards pcola
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Look how much convection is still over Haiti and DR.



Hope this moves on pretty soon, because I do not want headlines like 2004.
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The fact that there is any debate on whether the center is inland or not should prove that Isaac needs to move further away from land before he can strengthen much.
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New Iberia, LA here. I'm worried, but not for myself. I'm paying close attention for my family in Chalmette. They're too close to uncertainty right now for me to breath a sigh of relief. I remember how Katrina kept shifting further and further west with each advisory, until they were essentially in the crosshairs. Seems like we'll have a day or two to figure out if they're coming over for a visit.
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Calling someone a wishcaster should be worthy of a ban on here. I never use it, same with downcaster. Causes too much drama in a place where drama shouldn't exist. The people who call the entire blog a load of wishcasters should honestly get off their high horse and actually attempt to listen to what we're talking about instead of generalizing. Same with people who call people downcasters.
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998.1 millibar pressure.
Member Since: July 6, 2010 Posts: 113 Comments: 32822
As dry as it has been here in the south a tropical force wind would bring down many trees. I am afraid we will see a lot of power outages as Isaac is so big.Far away from the coast will be affected and a quick heavy rain will cause massive flooding
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Quoting leelee75k:


Channel 10 in South Florida has Max Mayfield the former NHC director as their hurricane expert as well a pretty good team of mets. I like them!
Max is the best. No hype, just low key facts. One of my favorite NHC Directors; so glad he is on local Miami station.
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Quoting Tribucanes:


MOST??? of the people on the blog are wishcasting. I've seen posts like this over and over. I know this post got lots of pluses, ya'll must be reading a different blog than I; because I don't see that at all. People are excited by the models which bring the storm closest to them. Guess why? Because it well may. Saying they WANT to be hit by a monster Isaac is a very big leap. I'm sure someone will post something in an hour stating the same ridiculous thing because it'll get lots of pluses. I'm sure SOMEONE or two may WANT to get hit directly by a major. Rest assured MOST do not in any way.


I think alot plussed it because of his loss and understanding how he doesn't want another to hit someone the same way.
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Just North of Guayacán, Holguín
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1977. Levi32
Quoting MississippiWx:
Center has most likely just emerged offshore. Will be interesting to see if recon can get close enough.


They are trying hard. 998mb is the new extrapolated pressure minimum.

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1976. Caner
That Low over Cuba to the NW of Isaac is beginning to look better in its own right...

A Fujiwhara effect in the gulf would be photogenic...
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Quoting kbjone:


Live in Bourg, work in Houma, definitely watching it here.


Baton Rouge, here. Definitely watching!
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Quoting MississippiWx:
The super rapid scan visible loops show that the center is inland. It will pop back out over water since it is just over a point that juts out. If it keeps its current heading, it will parallel the coastline for a while.


That's what I see too. I was about to breathe a sigh of relief, and then GFS pulled a "psyche!". Could you explain the trough and what's pulling this thing westward?
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Expect tropical storm warnings to be issued for the west central florida coast and hurricane watches may be required for the northern gulf coast from mobile to apalachicola,fl later tonight
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Quoting Tribucanes:


MOST??? of the people on the blog are wishcasting. I've seen posts like this over and over. I know this post got lots of pluses, ya'll must be reading a different blog than I; because I don't see that at all. People are excited by the models which bring the storm closest to them. Guess why? Because it well may. Saying they WANT to be hit by a monster Isaac is a very big leap. I'm sure someone will post something in an hour stating the same ridiculous thing because it'll get lots of pluses. I'm sure SOMEONE or two may WANT to get hit directly by a major. Rest assured MOST do not in any way.


Yes I am a Wish caster,,, I wish it stay away from LA,,,,
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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.

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