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 LargoFl:
yes and traveled all along the northern gulf into texas geez..i sure hope THAT model is wrong


WOW. Ok, it wasn't just my imagination. With the path this storm has taken, I thought I was maybe just loosing my mind haha
Member Since: December 31, 1969 Posts: Comments:
hey guys anyone have any obs for Great Inagua Island pleas post it thanks
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Quoting MiamiHurricanes09:
First time that I get a real good look at the surface circulation: NRLMRY Visible Loop.

Correct me if I'm wrong, but am I the only one that is seeing the circulation move from Imias, Cuba in in the southeastern tip, and jog due north to near Baracoa, Cuba, on the northeastern tip over the past 90 minutes? If you speed up the loop sufficiently, you'll see a tight surface circulation executing that motion. Thoughts?


I was thinking exactly the same thing. I think he's emerging off of Cuba.
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Quoting Wunderwood:


Then you see what I see. Someone on another forum with knowledge of atmospheric physics posted that the center might migrate to the cloud mass NE of the previous center fix. We shall see.



I see the LLC I'm not sure about the center reforming over water, what im sure is that he has jogged nothward again
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Quoting SELAliveforthetropic:


Me too ! It's like ok we good ... Oh maybe not.... Then we good again.... It is driving me crazy. With me being a weather nerd as some may call it everyone is asking me what will he do.... I just don't know....is all I can say lol


I know huh? The post below you shows models of this thing hitting around the LA/MS border. Other say the models shifted West as well. Not sure on what to do. Guess, just keep watching for now.
Member Since: December 31, 1969 Posts: Comments:
From what I can see the LLC is right on the N Cuba coastline, and traveling at an angle just slightly North of parallel to the coast line, and will ever so slowly pull away from Cuba. NHC is spot on with their track, at least for the short term.
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Quoting drs2008:
As a Biloxi resident,I have been thinking that we are out of the woods. Now im starting to get concerned.


Just keep watching and monitoring.

Right now Biloxi is on the furthest west of the models.
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Quoting JasonRE:


Largo, did the storm shift west violently at the end?
yes and traveled all along the northern gulf into texas geez..i sure hope THAT model is wrong
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First time that I get a real good look at the surface circulation: Link.

Correct me if I'm wrong, but am I the only one that is seeing the circulation move from Imias, Cuba in in the southeastern tip, and jog due north to near Baracoa, Cuba, on the northeastern tip over the past 90 minutes? If you speed up the loop sufficiently, you'll see a tight surface circulation executing that motion. Thoughts?
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Isaac is definitely starting to look more symmetrical again. Convection has been firing on the SW, and should fire on the NW when it gets a bit further from Cuba. I think he's organising again.
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Quoting StormJunkie:


Maybe so, but initially we just need to get in to the area ahead of potential traffic and will need to be in a location that has stable parking garages. That may end up being Pensacola or even Mobile, but will update that day by day until landfall. After the storm we will move out to the "forgotten" communities that we can best assist.


Props to you guys. I think PCB is a good starting point. Thanks for all you do!!
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Quoting Bielle:
Hi all: I haven't been able to get onto the NHC site in two days. Could the access be limited to those in the possible cone, or to those in the U.S.? (Canada here.) Has anyone else had this problem? Here is the address I am using: http://www.nhc.noaa.gov/


I'm in the UK and haven't had a problem. Try a different browser? The address is correct.
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Good Day/Evening to all. Hear our boy Issac had a semi-rough night last night?? Is his structure still alive and well?
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As a Biloxi resident,I have been thinking that we are out of the woods. Now im starting to get concerned.
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There is some evidence of an apparent LLC not associated with Isaac, which is forming SW of Cuba near the Caymans.

I don't think it's developed yet, but the low-level wind barb overlay proves it's not an optical illusion. It's very close to the core of the Monsoon trough Isaac is embedded in, but WNW.

With all this convection on the N. Side of Cuba, it wouldn't take much to jump start that thing if some of the convection mass merges with it.
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Quoting RTSplayer:
Poll 1:

Will the next Euro be:

A, about the same as the previous.
B, West of the previous.
C, East of the previous.


Poll 2:

Will the next Euro do:

A, Left Hook (like the previous)
B, Right Hook
C, Straight In


Good poll!

B. West of previous

C. Straight in.

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Quoting HCW:
I have wood this morning .


Dude, you can NOT make it this easy! We're all a little punch-drunk as it is.
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Quoting GTcooliebai:
150 hrs. and Isaac is inland and flooding will be a major problem. Also here comes Kirk, so coffee will remain in the pot for the late nighters.



I think you mean "Kyle"
Quoting CaneHunter031472:
Please someone correct me. Did the GFS changed to the west? Seriously I need lost everything during Katrina and I am getting sick of my stomach now. Is this thing going to hit Mississippi. I just cannot go tru this again. Someone give me an educated guess so I can start moving the few things I do not want destroyed.


I pray you will not see a direct hit. I have a friend who used to live in Mississippi and the images from there were horrible. I know a lot think of NOLA when Katrina is mentioned but I remember the images portrayed for those in your area. I can't say that it will hit your area for certain since anything can happen but I don't think it would hurt to move a few things you might really want protected just in case. I wouldn't freak out though and try to remain calm. I know that is going to be hard to do but I do wish for the best for you. I am in South West Georgia. They are predicting a CAT 1 hurricane here. The last storm to do that here caused 6 twisters in my town. I saw one of them pass across the parking lot of the grocery store I worked at in 2004.
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Quoting GTcooliebai:
150 hrs. and Isaac is inland and flooding will be a major problem. Also here comes Kirk, so coffee will remain in the pot for the late nighters.



Kirk's a fish.
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Quoting wpb:
a recon would have trouble finding 40 mph winds now

I disagree.
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Quoting flcanes:

ehh, maybe a bit west


Maybe so, but initially we just need to get in to the area ahead of potential traffic and will need to be in a location that has stable parking garages. That may end up being Pensacola or even Mobile, but will update that day by day until landfall. After the storm we will move out to the "forgotten" communities that we can best assist.
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Hi all: I haven't been able to get onto the NHC site in two days. Could the access be limited to those in the possible cone, or to those in the U.S.? (Canada here.) Has anyone else had this problem? Here is the address I am using: http://www.nhc.noaa.gov/
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Quoting wpb:
a recon would have trouble finding 40 mph winds now


I wholeheartedly diasgree, but we shall see when recong get's in shortly.
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Quoting tennisgirl08:


I disagree. The models have been flip flopping between MS/AL coast landfall and PCB, Florida area.

They have never moved further west than Mobile/MS area and they probably won't.


You must have missed this mornings model runs. I thought there were two that had the storm hitting Louisiana this morning. The HWRF definitely had it on this run.
http://moe.met.fsu.edu/cgi-bin/hwrftc2.cgi?time=2 012082418-isaac09l&field=Sea+Level+Pressure&hour=A nimation
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696. wpb
a recon would have trouble finding 40 mph winds now
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Quoting WxLogic:
In regards Isaac's current position... earlier today the center appeared to be elongated W to E... now it seems the eastern section is taking over and it might be trying to set itself up over water as we speak (WSW of Great Inagua).


Then you see what I see. Someone on another forum with knowledge of atmospheric physics posted that the center might migrate to the cloud mass NE of the previous center fix. We shall see.
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Rick Scott just declared a State of Emergency in Florida...

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Quoting yoboi:


how long does it take you to move things and prepare??


Well, I don't want to sound materialistic, but I lost everything after Katrina, and it hurts. I think that I could get The couch which it was a huge sacrifice to buy it out of here in about 2 to 3 hours. I am getting my family photos and the deed to the house plus insurance info in a box today and to my Jeep tomorrow. That's all I can save everything else it's just impractical to move.
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692. CJ5
Quoting WxGeekVA:


My latest forecast map.
Unofficial


That is cetainly reasonable.
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Quoting LargoFl:
this is from 2am this run..but did you see what happened?


Largo, did the storm shift west violently at the end?
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Quoting Jedkins01:
The models are performing really poor even still with Isaac, however the chances of it being significant for my area and the RNC are decreasing once again, thanks to the models insistence on the ridge in the Atlantic quickly building back over Florida before it has a chance to curve farther right. I must the pressure gradient over Florida is rather strong right now. Which isn't typically what one would expect from a weakness between a high when a storm is approaching from the direction Isaac is.


While I have insisted on a Central or Eastern Panhandle or eastern panhandle landfall after first striking the keys with tropical storm force winds for the Tampa Bay area. Some of the new guidance like the new GFS suggests this area won't get anything now except breezy winds and showers and thunderstorms from tropical moisture, which is normal weather for this time of year anyway.


However a lot can still change, if I was the NHC, I would have my track further west where they have it for the sake of people, however since i am no weather authority I'm sticking with a central and eastern panhandle landfall for now just because I have doubted the ridge will rebuild in time because there is often a delay in time regarding model tendency for change in pressure systems. Of course that isn't always the case, but it often is.



Actually the models keep the ridge fairly weak. They must be seeing something else steering it that far west. I'm with Levi on a more eastern scenario.
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Quoting Levi32:


I'm pretty close to the consensus now (at least before the 12z GFS), just a tad to the east. A track like the 12z GFS still looks fishy to me, as it hasn't happened in 170 years since track records began, but you can't really say never with the weather.

The track has had to shift east in bits for the last couple of days, and we just saw the models flop for the 24-hour forecast due to the Caribbean mountains, so some things can still happen to the forecast in a span of 3 days. We'll see.


Agreed. Climatologically these storms always take a turn N, even NE as they move poleward in the GOMEX. So, I get your reasoning there.

We shall see.
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we are in the 60 mph zone in this cone and damn near the 75 mph zone
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Quoting WxLogic:
In regards Isaac's current position... earlier today the center appeared to be elongated W to E... now it seems the eastern section is taking over and it might be trying to set itself up over water as we speak (WSW of Great Inagua).



you may be right however week LLC is on cuban coast we'll have too see
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I just wish the GFS would initialize properly, again its 6 hour location is off by 50-75 miles south on the southeastern coast of Cuba instead of the northeastern coast.
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What would happen if the ridge to the north builds...any chances of a turn....Central florida here
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684. 900MB
Quoting STXHurricanes2012:

It was 978 mb not 918 lol


Phew! My eye sight is going!
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683. HCW
I have wood this morning . It's good thing cause some of the stores this morning in the Mobile area are running low if not out of most stuff and forget about finding a generator . Good luck to everybody in the path of this storm :)
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Quoting Wunderwood:



According to NHC at last report, Isaac was moving NW. Some on this board have it hugging the Cuban coastline which is dead wrong. Isaac may be reorganizing more to the north and east giving an appearance of a northerly movement, in my opinion.



I was just going to make that observation! I also believe that it will be quite evident in the next 2 hours that it has emerged in the Atlantic if current trends verify
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Quoting atmosweather:


Ahh your new track forecast is now west of my thinking...which means I might need to re-evaluate things haha. I am concerned that several models have now followed the HWRF in forecasting rapid intensification in the SE-ern Gulf of Mexico.

Why are you so far east then?
Member Since: December 31, 1969 Posts: Comments:
Poll 1:

Will the next Euro be:

A, about the same as the previous.
B, West of the previous.
C, East of the previous.


Poll 2:

Will the next Euro do:

A, Left Hook (like the previous)
B, Right Hook
C, Straight In
Member Since: December 31, 1969 Posts: Comments:
In regards Isaac's current position... earlier today the center appeared to be elongated W to E... now it seems the eastern section is taking over and it might be trying to set itself up over water as we speak (WSW of Great Inagua).
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Quoting Wunderwood:



According to NHC at last report, Isaac was moving NW. Some on this board have it hugging the Cuban coastline which is dead wrong. Isaac may be reorganizing more to the north and east giving an appearance of a northerly movement, in my opinion.


does look like it may be reforming i really dont know to be honest upper keys 90 mph cane in my forecast
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676. wpb
ships decay model on track here.
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6 hours old. Hopefully will have a newer one soon.
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168 hrs.

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673. 7544
looks like he just took a little north jump hmmmmmm
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Quoting chrisdscane:



could SE FL still see a direct hit


We are in the cone, so I would say yes... At least the southern part of Dade is..
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Quoting flcanes:

there are millions of lives in the balance
by the way, how many dead in haiti yet

I think the count now is 3. Might seem low but that's still horrible.
Not sure I could be wrong.
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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