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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They're just using the inputs that are on the ground so to speak.  They're not sentient.
Quoting louisianaweatherguy:
GFS and the GFDL/EURO have swapped places on this model run... THEY REALLY HAVE NO CLUE AT THIS POINT.... we need 2-3 consistent runs!!!!!

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Quoting KeyWestbeachcomber:

Thanks for your kind words...Still fishing around on the blog WONDERING bout storm surge in KEY WEST..any input weatherpeeps?


this copied from post #1347:

STORM SURGE...THE COMBINATION OF A STORM SURGE AND THE TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY RISING WATERS. THE WATER COULD REACH THE FOLLOWING DEPTHS ABOVE GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

SOUTHWEST FLORIDA COAST...5 TO 7 FT
SOUTHEAST FLORIDA COAST AND THE FLORIDA KEYS...1 TO 3 FT
HISPANIOLA AND EASTERN CUBA...1 TO 3 FT
THE BAHAMAS AND TURKS AND CAICOS...1 TO 3 FT
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1469. Michfan
Link
Quoting duprk452:
Can someone please post the latest Euro? Thanks!

Link
Member Since: September 7, 2007 Posts: 0 Comments: 1736
1468. Hhunter
ECMWF pretty much matches bastardi forecast path and intensity of a 2-3. He expects tropical storm conditions up east coast
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Quoting catastropheadjuster:
So can Alabama breathe a sigh of relief know, since everything is pointing to Florida. I don't wish no harm to Florida. Just trying to figure out what we need to do. We have 2 boats off the trailors on stands in the air working on them and if by chance it might come this way we need to get them down and batten down the shop and tell folks to come get there boats.


sheri


Absolutely not. Keep a close eye on this storm.
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Quoting MiamiHurricanes09:
So now the GFS is thinking central Florida panhandle. Nice.

Give up the crown to the GFS, Europe. ;)


???? The GFS went west. The Euro went East.
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1465. SLU
25/1800 UTC 14.7N 32.2W T1.5/1.5 97L -- Atlantic


SHOWERS AND THUNDERSTORMS REMAIN DISORGANIZED IN ASSOCIATION WITH A
BROAD AREA OF LOW PRESSURE
LOCATED ABOUT 400 MILES WEST-SOUTHWEST
OF THE CAPE VERDE ISLANDS. SLOW DEVELOPMENT OF THIS SYSTEM IS
POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT MOVES TOWARD THE
WEST-NORTHWEST AT 10 TO 15 MPH. THIS SYSTEM HAS A MEDIUM
CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

This system is better developed than the NHC thinks ....


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Quoting duprk452:
Can someone please post the latest Euro? Thanks!



we been posting it learn too follow the blog more and you wont miss it
Member Since: May 21, 2006 Posts: 5091 Comments: 115354
1463. Seastep
Quoting MarcoIslandCat5:
Broward schools all closed Monday.


Now THAT is premature.
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Quoting Levi32:
And look at the recurve into the Carolinas. The pattern and history strongly supports this track. Nothing is guaranteed though.

Usually once the ECMWF corrects within 3 days of landfall it has corrected the "correct" way.



Yeah, I agree, recurve makes more sense.
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Quoting WxLogic:


HH Recon should be in Isaac in 15 to 30 min.

G-IV Survey is already making its rounds.

Thank you!
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GFS and the GFDL/EURO have swapped places on this model run... THEY REALLY HAVE NO CLUE AT THIS POINT.... we need 2-3 consistent runs!!!!!
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1459. Drakoen
Indeed, we are in the range that the ECMWF is know for. Still thinking that Issac will be a panhandle landfall.
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Can someone please post the latest Euro? Thanks!
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Quoting FLWeatherFreak91:
Do any of you guys recall me repeatedly calling for a NE recurve in the Gulf?

I mentioned it once, was tempted again but didn't want to be called a wishcaster because of my username. If it slows down, it would pick it up NE over the Gulf.
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Quoting catastropheadjuster:
So can Alabama breathe a sigh of relief know, since everything is pointing to Florida. I don't wish no harm to Florida. Just trying to figure out what we need to do. We have 2 boats off the trailors on stands in the air working on them and if by chance it might come this way we need to get them down and batten down the shop and tell folks to come get there boats.


sheri

NO it is equally as likely to slam AL as FL and regardless, AL will be affected
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Quoting TomballTXPride:
Cuba is the wildcard. The ultimately player right now.


I Agree, after it comes off Cuba and we see where it is really located.. and which way it is headed..

we will know better....

more waiting and watching.....

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1453. Michfan
Quoting scott39:
Now the EURO is all of a sudden the Model to follow. Some of you crack me up! Lol, Both the EURO and the GFS are very good models, but until they both match up for more than 1 model run or even 2 or 3...the exact track is still uncertain in the GOM.


00Z and 12Z are almost always more poleward than the 18Z and 06Z are because the 18Z and 06Z are extrapolated where the other two are not. We've seen this happen with them flip flopping many times over the years. Its nothing new. Get used to it. Intensity of the storms is a huge factor as to where they will go and models do not predict intensity well at all. The HWRF is probably the best at it.
Member Since: September 7, 2007 Posts: 0 Comments: 1736
Quoting louisianaweatherguy:
It's funny how all the FLorida people bad mouthing the EURO model not too long ago now think its the right model to follow... really funny...

Here's the facts:
Florida Keys will get rocked by a Cat 1 Hurricane (at least a cat 1)
after that, New Orleans to Tampa Bay need to watch out for a MAJOR HURRICANE!!!
Unfortunately most if not all the models are calling for this now, however there is still time for that to change.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
So now the Euro is thinking central Florida panhandle. Nice.

Give up the crown to the GFS, Europe. ;)
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1450. WxLogic
Quoting Maineweatherguy20023:

When is HH recon in next??


HH Recon should be in Isaac in 15 to 30 min.

G-IV Survey is already making its rounds.
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Quoting louisianaweatherguy:
It's funny how all the FLorida people bad mouthing the EURO model not too long ago now think its the right model to follow... really funny...

Here's the facts:
Florida Keys will get rocked by a Cat 1 Hurricane (at least a cat 1)
after that, New Orleans to Tampa Bay need to watch out for a MAJOR HURRICANE!!!

AGREE 100%
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1448. wpb
recon 23k to 8k in 10 min ready to work
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Quoting NOLALawyer:
This place is going to go nuts over the next 4-5 days.

Moby Dick is rounding the bend and about to enter the Gulf.

It has been a long time since this scenario played out....
You are right! Also I am a NOLA Lender!
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Quoting LargoFl:
NHC_Surge @NHC_Surge
NHC forecasting 5-7 ft storm #surge with #Isaac for portions of SW FL, 1-3 ft for SE FL and the Keys 1.usa.gov/MQ2V7L


Thanks Largo..thats what I was looking for....appreciated:)
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BLOG UPDATE

Tropical Update: Tropical Storm Isaac (2:30p.m EDT)
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1443. Levi32
And look at the recurve into the Carolinas. The pattern and history strongly support this track. Nothing is guaranteed though.

Usually once the ECMWF corrects within 3 days of landfall it has corrected the "correct" way.

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looks like the euro is right on 85W weak cat 3 at landfall
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A track just to the west of Panama City would be the worst case scenario. Not only will storm surge be an issue for Panama City Beach, but all that water may get backed up into the bay and potentially cause some flooding in downtown Panama City.
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Quoting NEPASteve:
There's still a chance it runs up the east coast, right?

Hate to say it but not really
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Quoting WPBHurricane05:


StormTop?


rofl!!! I know, sounds just like him,, well
almost
STORMTOP TYPES IN ALL CAPS!!!!

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Quoting NEPASteve:
There's still a chance it runs up the east coast, right?

No.
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It's funny how all the FLorida people bad mouthing the EURO model not too long ago now think its the right model to follow... really funny...

Here's the facts:
Florida Keys will get rocked by a Cat 1 Hurricane (at least a cat 1)
after that, New Orleans to Tampa Bay need to watch out for a MAJOR HURRICANE!!!
Member Since: Posts: Comments:
Broward schools all closed Monday.
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So can Alabama breathe a sigh of relief know, since everything is pointing to Florida. I don't wish no harm to Florida. Just trying to figure out what we need to do. We have 2 boats off the trailors on stands in the air working on them and if by chance it might come this way we need to get them down and batten down the shop and tell folks to come get there boats.


sheri
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Quoting WxLogic:
We'll see how things keep rolling after fresh G-IV data goes in tonight.

For now, I'm finding it hard for Isaac to get past 85W without the Central CONUS High somehow translating to E CONUS.

When is HH recon in next??
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1431. Drakoen
wow on the ECMWF lol. Interesting to see the ECMWF come this far east after it had been hanging on to a western solution.
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Quoting TampaFLUSA:

But none of the models up to this point like the new euro have shown a recurve NE in the Gulf like this run.
Do any of you guys recall me repeatedly calling for a NE recurve in the Gulf?
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1428. LargoFl
NHC_Surge @NHC_Surge
NHC forecasting 5-7 ft storm #surge with #Isaac for portions of SW FL, 1-3 ft for SE FL and the Keys 1.usa.gov/MQ2V7L
Member Since: August 6, 2011 Posts: 4 Comments: 40959
1427. scott39
Now the EURO is all of a sudden the Model to follow. Some of you crack me up! Lol, Both the EURO and the GFS are very good models, but until they both match up for more than 1 model run or even 2 or 3...the exact track is still uncertain in the GOM.
Member Since: June 13, 2009 Posts: 0 Comments: 6886
Quoting GetReal:
NOGAPS 12Z 108 hours


MS/AL line?

Regardless NOGAPS is too weak based on that. at LEAST CAT 2 more likely CAT 3
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Geez, Euro right over my house at 120 hours. Where did that come. But still off on the first 24 hours compared to NHC, so who knows whats going to happen!
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Quoting Spartan117:
This will blow up in 12-18 hours and graze south florida as a minimal cat 2. I will be back to say told you so.


StormTop?
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There's still a chance it runs up the east coast, right?
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1422. Michfan
Quoting GTcooliebai:
120 hrs. recurving into Savanna? Change of events here, trough must be stronger, causing the Northwestern Flank of the High to erode.



That actually has the center right over Augusta, GA, which is where i am at. Fort Gordon is gonna have some fun if this holds true.
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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.