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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Quoting GTcooliebai:
48 hrs.


ri alert
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420. 892mb
Quoting Hhunter:


Bastardi warns of up to cat 2/3 just past or at Floriday upper keys.. danger if slips more to the right toward miami. Check out surge potential miami south with a CAT 2 10-12 feet. A danger to be aware of depending on movment and strength.


Only "free" to subscribers - HA!!
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419. USF04
Long time lurker, first time poster. Don't worry you won't here much nonsensical drivel from me, but I do have some questions on occasion. I was just wondering what a weaker storm means for a track in comparison to a stronger storm.
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Quoting Clearwater1:


Quoting Jedkins01:



Punta Gorda wasn't in the cone as Charley approached.

*****
SE FL wasn't in the cone as Wilma Approached either.
*****

Exactly. Nice we have long range radar, out of Tampa and Key west to watch it's progress off shore. See if it is indeed heading nw as it gets closer.

it is heading northwest, nearly nnw
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48 hrs.

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Quoting Elena85Vet:
Isaac certainly struggled in what was previously expected to be optimum conditions for intensification.
So far through current difficult conditions he's catching some breaks regarding not having his center cross the most rugged terrains of Hispaniola. If he catches a couple more breaks (Cuba/S. Fla) he's got the potential to be one heck of a tracking storm through the Gulf.

he actually pulled together just fine last night
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Quoting E46Pilot:


SE FL wasn't in the cone as Wilma Approached either.


Quoting Jedkins01:



Punta Gorda wasn't in the cone as Charley approached.

*****
SE FL wasn't in the cone as Wilma Approached either.
*****

Exactly. Nice we have long range radar, out of Tampa and Key west to watch it's progress off shore. See if it is indeed heading nw as it gets closer.
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If you are in the future impact zones, please get some mosquito repellant as one of your supply item..with the flooding expected from Isaac and standing water around for some days will tend to bring out the mosquitos in full force..the west nile virus is at epidemic levels and you dont need to chance it without having some protection to fight them off
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Quoting KEEPEROFTHEGATE:

florida keys are in trouble now
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Isaac certainly struggled in what was previously expected to be optimum conditions for intensification.
So far through current difficult conditions he's catching some breaks regarding not having his center cross the most rugged terrains of Hispaniola. If he catches a couple more breaks (Cuba/S. Fla) he's got the potential to be one heck of a tracking storm through the Gulf.
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Quoting MarcoIslandCat5:
...here on marco island... Anyone have a prediction of surge here? Tia


Some info HERE.
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42 hrs.

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Quoting connie1976:

Oh, wow!

this because of isaac
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Quoting Hhunter:
Link

check out bastardi free video..


Bastardi warns of up to cat 2/3 just past or at Floriday upper keys.. danger if slips more to the right toward miami. Check out surge potential miami south with a CAT 2 10-12 feet. A danger to be aware of depending on movment and strength.
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Quoting E46Pilot:
Are you guys seeing a very prominent NNW movement like I am?
no maybe nw though
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Quoting Dakster:
Water main broke in Miami Beach... Not a good time to millions of gallons of water gushing into the streets.

Oh, wow!
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Quoting LargoFl:
it's more like 100% for us! 110% really ;)
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Are you guys seeing a very prominent NNW movement like I am?
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Quoting gbreezegirl:
Yeah you guys keep h im in Tampa - don't need him up here.

hehe you don't really have much of a choice.
cannot believe this thing is going to landfall where you've already had so much rain.
hope the handle doesn't come off the pan!
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So what kind of surge can we expect here? Getting worried now
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Quoting cdo:
Issac gets the title of.....The Most Overhyped Storm of the Century? Looks like the drought of a major will continue...
No one is hyping the storm on here. No one is saying it'll be Category 4 or 5.
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GFS at 36 hours....................remember..250 miles wide
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Link

check out bastardi free video..
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Quoting cdo:
Issac gets the title of.....The Most Overhyped Storm of the Century? Looks like the drought of a major will continue...
That title belonged to Irene.
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Quoting KEEPEROFTHEGATE:

oh no no no no
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Quoting Chicklit:

Too soon.
He'll show up in Tampa before that imo
Yeah you guys keep him in Tampa - don't need him up here.
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Quoting Jedkins01:



Punta Gorda wasn't in the cone as Charley approached.


Punta Gorda was in the cone, everyone was too focused on the track leading to Tampa Bay though.
There were communication issues between NWS and local weather stations but the fact is Punta Gorda was within the cone.

http://www.nws.noaa.gov/os/assessments/pdfs/Charl ey06.pdf
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387. cdo
Issac gets the title of.....The Most Overhyped Storm of the Century? Looks like the drought of a major will continue...
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30 hrs.

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Quoting RevInFL:
So what is everyone's take on the weather we will get here on the Space Coast? I am supposed to leave for the panhandle and was wondering how much prep should I do here first.

Isaac is huge - TS Winds 200+ miles from center. If I was there, I would be prepared - at least preliminary preps and keep a watch in case.
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Quoting flcanes:

that spells mudslides and cholera for haiti


Those people cannot catch a break. If it's not a cyclone, it's an earthquake. If not that, it was the Duvaliers.
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Quoting GTcooliebai:
GFS 12 hrs.

Can you continue to post this version?.Don't like the other one.
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It's like Isaac wants to include the NW trough in his realm.
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Quoting BahaHurican:
They can't drop dropsondes over land. They don't want to kill somebody.

are you kidding me?????
(something falls out of the sky outside) lol
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Story updated to reflect information in the 11 a.m. advisory

A tropical storm warning is now in effect for Palm Beach County as well as the Treasure Coast. A tropical storm watch has been posted along the Florida east coast north of the Sebastian Inlet to Flagler Beach.

The National Hurricane Center made those changes as it issued its 11 a.m. advisory on Isaac.

A hurricane warning is now in effect for the Florida Keys including the Dry Tortugas and the west coast of Florida from Bonita Beach southward.

In South Florida, numerous showers and thunderstorms are expected today as winds increase ahead of Isaac.

These thunderstorms could contain damaging winds, dangerous lightning and very heavy downpours.

Tropical Storm winds and stormy conditions are still possible for Sunday and Monday.

At 11 a.m. the National Hurricane Center reported that Isaac is packing 60 mph winds.

It's moving northwest at 17 mph.

Isaac was disrupted a bit after moving across Haiti overnight. Little change of strength is expected today, but the storm could get stronger in 12 hours as it pushes away from land.

Isaac is expected to become a hurricane as it approaches the Florida Keys.

Winds will pick up in South Florida through the day Saturday.

Sunday expect rain and winds strengthening 30-40 mph later in the day. There will be gusts over 40 mph and heavy rain in spots.

Isaac could be a category 2 hurricane when it makes landfall near the Florida Panhandle Tuesday or Wednesday.
.

Read more: http://www.wptv.com//dpp/weather/tropical-storm-is aac-storm-to-interact-with-hispaniola-next-48-hour s-are-crucial-to-south-florida#ixzz24Zb038LQ
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Water main broke in Miami Beach... Not a good time to millions of gallons of water gushing into the streets.
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Quoting flcanes:
hmmm, is cantore in pensacola yet????

Cantore going to Tampa
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Convection is starting to fire around the COC again.

One benefit I see to Isaac moving north of Cuba, is that he will be cut off from the sinking drier air now positioned to the south of Cuba, and which is a temporary feature.

Topography shouldn't be a problem, given his enormous size. In fact, he'll be drawing from every TCHP hot zone nearby before long, and a storm this size shouldn't need to be directly over it to draw in adjacent heat potential, it's ambient for him.

Food will soon be available from every quadrant. It could become like a giant PAC-man and with four mouths, no matter which way he turns, there are plenty of ghosts, and they aren't running away.





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Quoting KEEPEROFTHEGATE:

not a good weekend to be in the bahamas for sure
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Quoting E46Pilot:
I don't know if the HH can get clearance to fly in Cuban airspace. So until it comes out of their airspace I don't think they can pinpoint the exact center.
They can't drop dropsondes over land. They don't want to kill somebody.
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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