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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Quoting reedzone:
FINALLY the EURO makes sense!



Meanwhile, the GFS continues on a western rampage. LOL
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Quoting TropicalAnalystwx13:
Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.
Amazing guy my condolence to the family.
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Quoting MiamiHurricanes09:
Northern Keys landfall? I'm in coastal central Miami-Dade, should I expect to be in that 58mph-73mph winds area tomorrow?


If Isaac is a Category 1 storm at landfall, expect 50-60 mph peak winds with gusts near hurricane strength.
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1668. flsky
Quoting Jedkins01:



I do, you and me both.


Yes, you're all delightfully prescient....
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Quoting StormHype:


Do you type with your tongue?




you no what POOF you go
Member Since: May 21, 2006 Posts: 5091 Comments: 114965
Quoting TropicalAnalystwx13:
Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.

:'(
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1665. JasonRE
Quoting MarkTodd2233:


Zachary, La here, have been glued to computer since 5am

Been glued to my computer before this thing had a name. When hurricane season starts, it's on! I've always loved tracking storms even since I was young. Watched the eye of Andrew pass over my home when I was 11. Since then, they have fascinated me. Wondering what this one will do with the flip-flop models lately. Even with the EURO going so far East, I still have my doubts.

Also, Largo posted some model back earlier today that showed this thing hooking violently West after or near before landfall and riding the coast to almost Texas. I'm still wondering if hit hits anywhere near AL/MS border will LA feel any of this storm even due to it's size. Will we get rains persisting more than an hour or two?
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RIP Neil Armstrong
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Quoting FLWeatherFreak91:
Do any of you guys recall me repeatedly calling for a NE recurve in the Gulf?



I do, you and me both.
Member Since: August 21, 2008 Posts: 0 Comments: 7404
1660. flsky
Had a line of rain come thru Ponce Inlet, FL about an hour ago. Had to rush out to bring in everything off the balcony b/c stuff was starting to blow around. By the time we got everything inside, the wind had died down. Oh well, at least we're prepared for everything else that will be coming. BTW, we face straight east toward the Atlantic!
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Remember the wave that spawned Isaac was responsible for killing 28 people and caused major flooding.Seems his terror has continued in the Atlantic and the U.S is next.
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Quoting MississippiWx:


So odd to see the GFS and Euro split ways again, especially with the GFS getting all of this extra data fed into it. I would have thought the GFS would keep status quo near Panama City. The GFS is also in good agreement with its ensembles.


I'm with you, MSX. The GFS is concerning.

Also, isn't the GFS known for overdoing troughs? So, wouldn't this mean the trough is for sure not going to be enough to erode the ridge and cause a huge weakness?
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1657. GetReal
I believe that the center is on the coastline over Baha Rio Seco, Cuba..... Waiting for Recon to confirm it.
Member Since: July 4, 2005 Posts: 204 Comments: 8856
Quoting WeatherNerdPR:

:(
Yes. Very sad to hear that.
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1000mb



990mb



970mb



950mb



940mb



below 940mb

Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting JasonRE:
Anyone from Louisiana care to weigh in on this conversation? Anybody still keeping an eye on this thing or not worried due to the cone being outside of LA? Lafayette here!


Lake Charles here. Im not to worried but keeping an eye out for any changes. Local mets say that the weather is supposed to be nice and breezy.
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Quoting TropicalAnalystwx13:
Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.

:(
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1652. Drakoen
Quoting MiamiHurricanes09:
Northern Keys landfall? I'm in coastal central Miami-Dade, should I expect to be in that 58mph-73mph winds area tomorrow?


I like the NHC track I just think the 72hr point should be shifted 50-70 miles east. Those winds are certainly possible in gusts.
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Quoting MarkTodd2233:


Zachary, La here, have been glued to computer since 5am
Here in Destrehan la...I'm standing by just in case..
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Quoting JasonRE:
Anyone from Louisiana care to weigh in on this conversation? Anybody still keeping an eye on this thing or not worried due to the cone being outside of LA? Lafayette here!
Not very concerned now. Just drop in every now an then to check things. The key time will be tomorrow afternoon when the storm is near Key West and where the NHC says the storm is going at that time. If they say toward LA at that time, then I will get into full hurricane preparation mode.
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Quoting TropicalAnalystwx13:
Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.


NO!!! This is terrible. OMG.
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Quoting TampaFLUSA:
RT @karenmcallister: RT @brianstelter: Longtime NBC News space correspondent Jay Barbree reports that Neil Armstrong has died at age 82.


Oh no! Very sad news!
Member Since: July 17, 2008 Posts: 0 Comments: 1242
Quoting weatherh98:


DID I SAY IT WAS NW????

ALL I FREAKING SAID WAS THAT IT WAS MOVING MORE WESTERLY THAN THOSE MODELS WERE PREDICTING

IT WILL CATCH THOSE MODELS AS IT MOVES WEST.

YOU GET GLASSES THEN PUT OUT INFO
You get a Lunesta, calm down, and get to bed. ;)
Member Since: September 2, 2009 Posts: 130 Comments: 21162
It appears as though Isaac has not weakened. And, if the center can make any more progress offshore it may be able to intensify...and possibly quickly.
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Quoting nrtiwlnvragn:


26





Link


So odd to see the GFS and Euro split ways again, especially with the GFS getting all of this extra data fed into it. I would have thought the GFS would keep status quo near Panama City. The GFS is also in good agreement with its ensembles.
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Quoting wpb:
wont get one its over land



its not overe land
Member Since: May 21, 2006 Posts: 5091 Comments: 114965
FINALLY the EURO makes sense!

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should Isaac continues to track over water, then south florida and the keys should expect a stronger storm.
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1641. flcanes
Quoting Levi32:
Recon gliding along the coast of Cuba now.


found circulation yet
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RT @karenmcallister: RT @brianstelter: Longtime NBC News space correspondent Jay Barbree reports that Neil Armstrong has died at age 82.
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Quoting chrisdscane:




TY we have fools here who think his center is still onshore


Dr. Rick Knabb on TWC just said it is onshore.
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1638. wpb
Quoting weatherh98:


wait or the vortex message
wont get one its over land
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Quoting GTcooliebai:
Euro 72 hrs.



Euro has 40 to 50 knot winds over Tampa at that point, shows you how big Isaac is and will be.


This is the farthest east I've ever seen the euro, interestingly enough I think it'd the best initialization of Isaac I've seen with the euro.
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1635. Levi32
Recon gliding along the coast of Cuba now.

Member Since: November 24, 2005 Posts: 635 Comments: 26611
Quoting Drakoen:


It seems based on that alone that Issac has remained on the eastern side of the models which is even more of a reason to give credence to the eastern solutions.
Northern Keys landfall? I'm in coastal central Miami-Dade, should I expect to be in that 58mph-73mph winds area tomorrow?
Member Since: September 2, 2009 Posts: 130 Comments: 21162
Sorry for the off topic post.

Astronaut Neil Armstrong has passed away.

82 yrs old, 1930-2012

RIP
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1632. wn1995


my latest thinking on isaac
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looks like he may be a hair north of the next forecast piont
Member Since: July 21, 2010 Posts: 0 Comments: 1142
Quoting JasonRE:
Anyone from Louisiana care to weigh in on this conversation? Anybody still keeping an eye on this thing or not worried due to the cone being outside of LA? Lafayette here!


Zachary, La here, have been glued to computer since 5am
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Quoting LAnovice:
Based on the winds that the HH are reporting - center is further north than the forecast points. I am looking at this incorrectly?


wait or the vortex message
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Quoting weatherh98:


also heading more westerly than predicted.

did u post a blog today? havent checked my email


Once again, Isaac is moving NORTHWEST at 15 mph. Stop sending out false information!
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Quoting MississippiWx:
Nrt, if you're around, how many dropsondes made it into the 12z GFS?


26





Link
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Quoting Maineweatherguy20023:

I did


Yeah when zoomed in...the COC is still a little tricky almost like vertical stacking is still not quite perfect.
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1625. JasonRE
Anyone from Louisiana care to weigh in on this conversation? Anybody still keeping an eye on this thing or not worried due to the cone being outside of LA? Lafayette here!
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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?
Don't know if these links have been posted. The NHC has created two user-friendly interactive storm surge maps for Isaac.

This one gives potential for exceeding a level you enter.

This one will give probabilities.

They're based on Google maps and you can zoom in on your area of interest. I imagine the values will change / update as the forecast does. Hope that helps you and others wondering about storm surge potential.

(Ps. Page down after you open the links.)
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Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.
Member Since: July 6, 2010 Posts: 113 Comments: 31917
Quoting weatherh98:


look at the date


You look at the date: Aug. 25 2012 18 UTC
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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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