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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Member Since: Posts: Comments:
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.
lol
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Quoting JLPR2:
97L is looking nicer, reminds me of a WPac storm in the making.

Looks too big for the Atlantic.
The pressures are really low across the Atlantic right now.Which makes bigger storms.Higher pressure makes smaller storms.
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Quoting GetReal:



Yeah I guess that the GFS is now the outlier to be thrown out.... LOL


I lol.

epic.
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Quoting JLPR2:
97L is looking nicer, reminds me of a WPac storm in the making.

Looks too big for the Atlantic.
Yeah they haven't been kidding around this year to come off so big!
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1416. GetReal
NOGAPS 12Z 108 hours


MS/AL line?
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Quoting Levi32:


The battle has reversed lol.


This is crazy! I would have thought just the opposite for the Euro....lol.

I don't agree with a stronger storm at this point which is taking it further east. What will make him stronger? I think he will hug the Northern Cuban coast for a little while and that will keep him in check...for now.

He is even getting sheared thanks to the low pressure area just NW of him.

I don't know. Tricky forecast.
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1414. 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.
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Quoting washingtonian115:
Is that a major the Euro is showing?.

Yep. Winds of about 115 mph.
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Quoting PensacolaDoug:


96 HR ECMWF
Mobile Bay

Wrong run.
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Quoting Tribucanes:
If this is anyone's first rodeo in the expected affected areas remember to kick the fridge and freezer up to their coldest settings and fill the bathtub up for washing and flushing purposes. Please do not drink it.
Yes and make all the ice you can..as it melts it is water to drink also..
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I think the thing to watch is how strong Isaac is between Cuba and South FL/FL Keys. HWRF/GFDL/Euro have a really strong storm already by that point and thus they have a more poleward movement. How much Isaac continues to interact with Cuba could be a good sign. He continues to move in tandem with the coastline and his circulation and core seem ragged. He has a long way to go before he gets himself together enough to strengthen.
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120 hrs. recurving into Savanna? Change of events here, trough must be stronger, causing the Northwestern Flank of the High to erode.

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Quoting Chicklit:

Hey, please keep in touch and let us know how you're doing.

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

If this is anyone's first rodeo in the expected affected areas remember to kick the fridge and freezer up to their coldest settings and fill the bathtub up for washing and flushing purposes. Please do not drink it. Love Florida, my Grandparents lived in St.Pete until their death and there's no place I enjoy more than Florida. It's times like this though; I'm glad to be in Wisconsin and not going through what a lot of ya are going to be. Good luck and I really hope these bombing out models are just driving drunk for the moment.
Member Since: April 18, 2012 Posts: 0 Comments: 2437
1406. emcf30
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Quoting reedzone:


The everglades won't weaken the storm like most landmasses do.. It's possible it stays a Hurricane throughout that track across Florida.


You are thinking it will cross SW Florida? A clip so to speak?
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1404. JLPR2
97L is looking nicer, reminds me of a WPac storm in the making.

Looks too big for the Atlantic.
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1403. Michfan
Quoting washingtonian115:
Is that a major the Euro is showing?.


Cat 2.
Member Since: September 7, 2007 Posts: 0 Comments: 1736
Quoting Bluestorm5:
Euro isn't posting on RaleighWX site anymore... HMM


12z re-curve into Panama City/Tallahassee region.

Pressure on lowest FRAME is 961mb, but those are 24 hour frames, so lowest pressure may actually be lower than that somewhere before or after that value.

974mb on the first inland frame, obviously after the 961mb frame off-shore.
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Come on really the Euro and the Gfs appear to hate each other they don`t want to agree with each other.
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Quoting STXHurricanes2012:

Thats the GFS not ECMWF




OOps... Grabbed the wrong one!
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Is that a major the Euro is showing?.
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Quoting weatherh98:

Gfs and euro switched up

But none of the models up to this point like the new euro have shown a recurve NE in the Gulf like this run.
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1396. GetReal
12z UKMET 96 hours
Member Since: July 4, 2005 Posts: 204 Comments: 8898
96 hrs. landfall looks like around Panama City:



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1394. LargoFl
NWS tweet..........NWS Tallahassee @NWSTallahassee
Current forecast is a cat 2 hurricane between Panama City and Destin Tuesday. Spread the word and get prepared now! #Isaac
about 3 hours ago
Member Since: August 6, 2011 Posts: 4 Comments: 40845
1393. KEEPEROFTHEGATE (Mod)
Quoting TampaFLUSA:

Links not showing up.
we had a problem here try next set of updated runs
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Quoting cchsweatherman:


Very interesting that seemingly the ECMWF has come east while the GFS and the ensembles have gone west. Still very much model disagreement even in the short term with Tropical Storm Isaac. All will depend on whether or not Tropical Storm Isaac is now truly leaving the Cuban coast and continuing its general northwest motion. In my opinion, still cannot rule out a potential hurricane hit on extreme South Florida at this point given that the storm has been trending further north and east than predicted over the past 24 hours or so.
convection is starting to get going over the NE part of the center , looking at all the info i agree with you looks like a middle keys to upper keys landfall
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Quoting Levi32:


I'm with the new Euro, which is now the old GFS. It's confusing I know lol.


im with the new gfs
the old euro
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Quoting KeyWestbeachcomber:

So far ONLY TOURISTS have been asked to leave..and if anyone is going to leave a pet..it would be a tourist!! lol

Hey, please keep in touch and let us know how you're doing.
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I dont think Isaac will have the time to become a cane before making landfall in the upper keys a 70mph storms seems resonable JMO
Member Since: July 21, 2010 Posts: 0 Comments: 1181
1388. A4Guy
Quoting weedpoet:
does anybody find the reposting of NHC advisories and discussions helpful on this blog? is there anybody who doesn't read them on their own? just wondering.


I agree...especially when the advisories, discussions, and graphics are posted multiple times...and satellite images...
The model images are helpful, since not everyone knows where to go for that info...but where to get NHC stuff is pretty widely known at this point. If you know enough to come to this blog, you know enough to go to the NHC site. If you don't...you should probably be wathing you local news instead. :)
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Quoting Bluestorm5:
Euro at 72 hr



Major Hurricane Isaac! Not Good...
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Quoting PensacolaDoug:


96 HR ECMF
Mobile bay

Thats the GFS not ECMWF
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1385. Michfan
G-IV has taken off as well.
Member Since: September 7, 2007 Posts: 0 Comments: 1736
Quoting GetReal:
54 hours


Into Tampa like many on here are looking for... Be careful for what you wish for...


Man it seems like those HWRF and GFDL are whacky.........how have they been performing?
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Quoting mcluvincane:
Euro looks mean with that intensity... most models now agree with stronger storm. To bad for the people in the panhandle, such a beautiful place


Got lots of family down there. I've been keeping them updated.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting LargoFl:
geez sooo much info on the nws on twitter...this from the humane society..............Evacuations have started in the Florida Keys. PLEASE take your pets

So far ONLY TOURISTS have been asked to leave..and if anyone is going to leave a pet..it would be a tourist!! lol
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1381. wpb
recon radar should be very helpful
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Quoting Seflhurricane:
center is now at 75W and 21 N moving NW



yep, maybe nnw
Member Since: July 21, 2010 Posts: 0 Comments: 1181
1379. KEEPEROFTHEGATE (Mod)
HWRF GLITCH SORRY
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Wow, Euro recurve!
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Quoting Levi32:
ECMWF looks farther east, curving up towards Florida panhandle.



Very interesting that seemingly the ECMWF has come east while the GFS and the ensembles have gone west. Still very much model disagreement even in the short term with Tropical Storm Isaac. All will depend on whether or not Tropical Storm Isaac is now truly leaving the Cuban coast and continuing its general northwest motion. In my opinion, still cannot rule out a potential hurricane hit on extreme South Florida at this point given that the storm has been trending further north and east than predicted over the past 24 hours or so.
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1376. Levi32
Quoting TallyWeather15:

So the GfS goes west and the Euro goes east. Where is this storm going?!?!?!?



I'm with the new Euro, which is now the old GFS. It's confusing I know lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26682
1375. LargoFl
nws on twitter said plan for issac onland between destin and panama city in northern florida
Member Since: August 6, 2011 Posts: 4 Comments: 40845
Euro looks mean with that intensity... most models now agree with stronger storm. To bad for the people in the panhandle, such a beautiful place
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1373. Levi32
Quoting TropicalAnalystwx13:
GFS went west, ECMWF went east.


The battle has reversed lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26682
More Doom for Florida.
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96 HR GFS
Mobile Bay
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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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