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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Meanwhile, on top of the world, the Arctic sea ice records are falling like dominoes.

Well on our way towards obliterating the 2007 minima for extent and overall volume is down over 60% since 2006.

http://neven1.typepad.com/blog/
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Quoting Charmeck:


That dry air wedge still has me worried. Look how those storms over FLA are reacting to it! If Isaac keeps moving as fast as he has been I'm still on the lookout that he could end further up the florida coast before crossing.


Ridge continues to build...

Link
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Quoting SykKid:
I'm willing to bet that recon finds a system far more disorganized and weaker then many of you guys think. Isaac looks like it may just get ripped apart completely.

And if not hahaha I'll be laughing
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Quoting LargoFl:
WE ARE NOT..OUT OF THE CONE OF DANGER

I think that track puts the storm about 100 mile from our area. I bet we get a lot of street flooding, beginning Monday, with the first outer bands. 100 miles away I don't think much wind, except with the a gust. I will be watching the radar up the coast to see if it decides to make a crazy turn in the last hours before passing us.
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Quoting Jedkins01:



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


SE FL wasn't in the cone as Wilma Approached either.
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Visible images close up show the center right on the eastern tip of cuba mainly over the windward channel headed into open water in an hour or so
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Quoting Ameister12:
Thanks Dr. Masters.

thanks
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Quoting StormHype:


Remember that the 'cone' is for a ground zero hit. It's a 200+ mile diameter storm, not a fishing boat.

It's better to look at the TS force wind probability map on the NHC site to gauge the 'weather' you should expect.

Another thing to note is a deepening storm (which it is expected to be doing while passing offshore) pushes the strongest winds down to the surface levels.


the cone is not ground zero..the cone is the margin of error that the storm could track..the center line will be considered ground zero of where the storm is predicted to make landfall..
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263. wpb
Quoting CJ5:
Exposed to the NW. Like all week, he struggles to get convection and a good CDO around the center. Isaac was able to do it briefly yesterday afternoon but land interaction messed it up. Shear is a little high, 20, to the NW but is ok in his current environment. There doesn't appear to be much dry air around the system. Water temps are in the 85deg range. It seems like Isaac has a lot of things going for him. I would expect some good strengthing today but we all hav watch the past 72 hours and didn't see it happen.

JB was on Fox a second ago, he said there is potential to spin up to a Cat 2/3 before SFL landfall.
jb on fox should be FIRED
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I found Dr. Masters' Loop Current tutorial very informative. It all comes down to the amount of stored heat energy that resides within the weather system.
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Quoting louisianaweatherguy:
wow Isaac will propbably travel on land now according to latest plot and motion... hmmm... maybe THAT'S why the models are indicating a more WNW-W track - A WEAKER storm... until the gulf that's when it should spin up and go norht to hit the panhandle... SHOULD hit the panhandle...

I'm still a little uneasy about this one for some reason....


What part of La do you live?
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Quoting Bluestorm5:


HH doesn't fly over land.

actually it does sometimes
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Florida is not out of TS wind cone AND NEVER WILL BE.

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That dry air wedge still has me worried. Look how those storms over FLA are reacting to it! If Isaac keeps moving as fast as he has been I'm still on the lookout that he could end further up the florida coast before crossing.
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Quoting StormHype:


It's a 200+ mile diameter storm, not a fishing boat.


Nice way of putting it.
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255. wpb
Quoting STXHurricanes2012:
I think recon will say the center is east where the nhc placed it...again!!!
old vortex they left area 5am
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Quoting johnbluedog69:

Seems like some rain and storms are headed your way now.Tornado warning for norfolk now!I am on the DelMarVa peninsula not too far away from you.Stay safe!!
Thanks.You do the same as well.I will be going to a picnic today and it seems like rain will disrupt it.The temps are suppose to be beautiful today only in the high 70's.
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253. CJ5
Exposed to the NW. Like all week, he struggles to get convection and a good CDO around the center. Isaac was able to do it briefly yesterday afternoon but land interaction messed it up. Shear is a little high, 20, to the NW but is ok in his current environment. There doesn't appear to be much dry air around the system. Water temps are in the 85deg range. It seems like Isaac has a lot of things going for him. I would expect some good strengthing today but we all hav watch the past 72 hours and didn't see it happen.

JB was on Fox a second ago, he said there is potential to spin up to a Cat 2/3 before SFL landfall.
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The bad thing is looks like isaac wants not interact with cuba bad news for the people in florida



Here in dominican republic the rivers are starting to overflowing...........nearly 30 hours of continuous rain
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Quoting TomballTXPride:

NHC are trained professionals with PhD's. They are the best in business, with a strong mission to make the best forecasts off of science and all the sophisticated tools at their disposal to keep the public safe and informed.

They do not guess. That is completely false.

Incorrect then why do we have recon there for??? lol will see remember what happen a few days ago
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I just want to note that the NHC has taken SFL and east Florida out of the cone but yet have TS watches and warnings could mean they are not certain how the center will react once if crosses over cuba..any deviation to the left or right will make a difference in track and impact..
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Quoting clwstmchasr:


My bad. We're just inside.



Hmmm In cone, outa cone, in cone, outa cone....pointless IMO.
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Quoting clwstmchasr:
I see that Tampa is now out of the cone. We'll get some good rains with 30-40mph winds



Punta Gorda wasn't in the cone as Charley approached.
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Quoting STXHurricanes2012:
Actually now it looks abit too far west again! NHC seems to be guessing!!
Why would they be guessing? That is a ridiculous statement.
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If, as the NHC forecasts, Isaac makes landfall with 100mph winds, it would be the strongest landfalling Atlantic hurricane since Richard of 2010, and the strongest US landfalling hurricane since Ike in 2008.
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Quoting Relix:
So, where is wunderkidcayman seeing that SW movement again? :P!

HA..HA..HA..very funny...
NOT

no but I do see it moving W maybe just a tad N of due W
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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.


HH doesn't fly over land.
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sorry guys but that cone is going to be shifted back east later today. Hate to say it but Northern dade & Southern broward maybe in for a direct impact. Never look at the exact center like they say but if you follow a NW motion like they are saying Dade & Broward are right in line.
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Quoting LargoFl:
stay tuned , next advisory we will be back in it, then the 11pm we will be out of it, then the 2am we will be back in it lol


Remember that the 'cone' is for a ground zero hit. It's a 200+ mile diameter storm, not a fishing boat.

It's better to look at the TS force wind probability map on the NHC site to gauge the 'weather' you should expect.

Another thing to note is a deepening storm (which it is expected to be doing while passing offshore) pushes the strongest winds down to the surface levels.
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Quoting washingtonian115:
Hey Isaac you can park over D.C as a weak storm.We really need the rain and wouldn't mind having a day or two of rain.

Seems like some rain and storms are headed your way now.Tornado warning for norfolk now!I am on the DelMarVa peninsula not too far away from you.Stay safe!!
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Hard to argue this also.......center pretty obvious all morning

Link
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Quoting wpb:
thanks for that post


Many thanks for sure... Let's hand out phone numbers and coordinate posts. Yea... That's it.
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Quoting Relix:
So, where is wunderkidcayman seeing that SW movement again? :P!

He's probably crying because they discontinued the TS Watch for the Caymans. :P
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Quoting LargoFl:
WE ARE NOT..OUT OF THE CONE OF DANGER
Is not the cone of danger the white area? So, like I mentioned as well still in the cone.
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Won't be surprised of LLC reformation further NE... but we'll see... HH will hopefully be out in 20 min.
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Quoting washingtonian115:
Going to therapy because Isaac did not coming his way.ROFLMAO!.
LOL Maybe in Octuber or November he will see a storm that move over him as tropical cyclones tend to affect that area in those months.
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Quoting BoroDad17:


Yeah its conflicting info, NHC says just off coast in discussion, but coordinates they gave are on land according to my tracking chart.

It is incredible, that with all the tools available, and the costs of such, there is no definitive centre-location at the moment.

Silly, really.....
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Key West--Monroe County press conference now scheduled for 1pm EDT. (These things usually start late.)
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Quoting ncstorm:


yeah this time its looks to be them for landfall but impacts will be felt well inland with flooding..
Mets here in D.C said that we need to be on the look out for remnants that could bring rain with them.I'm not complaining over here :).
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Quoting LargoFl:
stay tuned , next advisory we will be back in it, then the 11pm we will be out of it, then the 2am we will be back in it lol
lol, we are still in the 11 am cone, or am I missing something?
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227. DVG
Quoting IceCoast:


Goes-14 1 minute scan. Zoom all the way in on the eastern tip of Cuba. Hard to argue with that


True dat.
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WE ARE NOT..OUT OF THE CONE OF DANGER
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Quoting clwstmchasr:
I see that Tampa is now out of the cone. We'll get some good rains with 30-40mph winds


Did they move the city? 'Cause it still looks like it's in the cone to me.
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I think recon will say the center is east where the nhc placed it...again!!!
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Quoting nrtiwlnvragn:





Thanks for that graphic nrti! :) Looks perfect to me.
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Quoting Clearwater1:
and where do you see that?
Maybe Tampa moved to the East coast?
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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