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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96 HR GFS
Mobile Bay
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Quoting Levi32:
ECMWF looks farther east, curving up towards Florida panhandle.


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

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Quoting Levi32:
ECMWF looks farther east, curving up towards Florida panhandle.




Seems most of the models are now agreeing on a Mobile, Al to Panama City, FL landfall... probably in the middle of that, near Destin. Question is where... Mobile to Panama City is about 150 miles... big difference and could result in worse weather for some.
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SUMMARY OF 200 PM EDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...20.8N 75.3W
ABOUT 40 MI...65 KM N OF GUANTANAMO CUBA
ABOUT 325 MI...525 KM SSE OF NASSAU
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES
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Quoting dader:


I understand. It just seems like they could have waited until tonight/Sunday morning with the uncertainty. Closing schools has an incredible impact- especially for someone who has children in North Dade schools and I am expected to be at work for TS force winds- it's Florida not New England.
..yes..and our schools are also... most of them..shelters..so they need to open the shelters and staff them..ahead of the time..as for your job..it IS florida and mostly they also close..unless you are in the medical field..most briges are closed to the mainlands and people are encouraged to stay home...
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1366. GetReal
Quoting weatherh98:

Gfs and euro switched up



Yeah I guess that the GFS is now the outlier to be thrown out.... LOL
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1365. Dakster
Quoting TropicalAnalystwx13:
GFS went west, ECMWF went east.


Naturally...
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Euro 72 hrs.

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This place is going to go nuts over the next 4-5 days.

Moby Dick is rounding the bend and about to enter the Gulf.

It has been a long time since this scenario played out....
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1362. LargoFl
Quoting Dakster:


I am assuming you got it back -- that isn't so bad. It is when the beginning of the storm takes out the power and you get to wait several days for it to come back on.

Waiting for a break (or at least a slow down) of the rain so I can grab the generator out of the shed and fire it up...
yeah this is oner thing in a storm we have to prepare for
Member Since: August 6, 2011 Posts: 4 Comments: 37144
GFS went west, ECMWF went east.
Member Since: July 6, 2010 Posts: 113 Comments: 31589
When does the next Euro run come out?

Never mind. Just saw it.

THX!!!!
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Euro at 72 hr

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1358. 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
Member Since: August 6, 2011 Posts: 4 Comments: 37144
Quoting GetReal:



Euro has now gone way east...

Gfs and euro switched up
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Quoting CybrTeddy:
For summary sake for people who can't read as fast or don't have the access to the tools some of us do.

The ECMWF, GFS, CMC, NOGAPS, GFDL, HWRF are all showing a formidable hurricane developing from Isaac in the Gulf as it passes through the Keys. Issac has emerged from Cuba per latest satellite and radar images, but do not expect intensification today as Isaac will be working on rebuilding its elongated core from it's ordeal with Haiti and Cuba. After that, intensification at a fairly decent pace is likely. There is little to stop this storm as dry air is a non factor and shear will lessen once Issac's somewhat displaced Upper Level Anti-Cyclone (ULAC) begins to become stacked over it.


Great job, thanks!
Member Since: August 29, 2005 Posts: 298 Comments: 40887
center is now at 75W and 21 N moving NW
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looks like he may be a bit north of the next piont
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1353. Dakster
Quoting LargoFl:
maybe that might go for all of us..we lost power the other night just from a thunderstorm grrrrr


I am assuming you got it back -- that isn't so bad. It is when the beginning of the storm takes out the power and you get to wait several days for it to come back on.

Waiting for a break (or at least a slow down) of the rain so I can grab the generator out of the shed and fire it up...
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1352. Levi32
ECMWF looks farther east, curving up towards Florida panhandle.

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Quoting Maineweatherguy20023:

Too fast.

No its not...seems reasonable.Its not like its showing cat 3 in 48 hrs!
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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.
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1349. Michfan
Recon over the Bahamas heading WSW towards Issac. Shouldn't be long till we have some data flowing in.
Member Since: September 7, 2007 Posts: 0 Comments: 1667
1348. GetReal



Euro has now gone way east...
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Here's an excerpt from NHC Tropical Storm ISAAC Public Advisory at 2 p.m.

HURRICANE CONDITIONS ARE EXPECTED IN THE HURRICANE WARNING AREA IN SOUTHWEST FLORIDA AND THE FLORIDA KEYS ON SUNDAY...WITH TROPICAL STORM CONDITIONS EXPECTED BY EARLY SUNDAY.

HURRICANE CONDITIONS ARE POSSIBLE IN THE HURRICANE WATCH AREA IN SOUTHEAST FLORIDA ON SUNDAY...WITH TROPICAL STORM CONDITIONS EXPECTED IN THE TROPICAL STORM WARNING AREA IN FLORIDA BY EARLY SUNDAY. TROPICAL STORM CONDITIONS ARE POSSIBLE IN THE TROPICAL STORM WATCH AREA IN FLORIDA BY SUNDAY NIGHT OR MONDAY.

STORM SURGE...THE COMBINATION OF A STORM SURGE AND THE TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY RISING WATERS. THE WATER COULD REACH THE FOLLOWING DEPTHS ABOVE GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

SOUTHWEST FLORIDA COAST...5 TO 7 FT
SOUTHEAST FLORIDA COAST AND THE FLORIDA KEYS...1 TO 3 FT
HISPANIOLA AND EASTERN CUBA...1 TO 3 FT
THE BAHAMAS AND TURKS AND CAICOS...1 TO 3 FT

THE DEEPEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST IN AREAS OF ONSHORE FLOW. SURGE-RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE SURGE AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT DISTANCES. FOR INFORMATION SPECIFIC TO YOUR AREA...PLEASE SEE PRODUCTS ISSUED BY YOUR LOCAL WEATHER SERVICE OFFICE. NEAR THE COAST... THE SURGE WILL BE ACCOMPANIED BY DANGEROUS WAVES.

SURF...DANGEROUS SURF AND RIP CURRENT CONDITIONS WILL AFFECT HISPANIOLA...THE BAHAMAS...THE TURKS AND CAICOS...EASTERN AND CENTRAL CUBA...AND THE EAST COAST OF FLORIDA AND THE FLORIDA KEYS DURING THE NEXT COUPLE OF DAYS. PLEASE CONSULT PRODUCTS FROM YOUR
LOCAL WEATHER OFFICE FOR MORE INFORMATION.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 PM EDT.

$$
FORECASTER BEVEN
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center of isaac is re emerging off the NE tip of cuba
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Quoting KEEPEROFTHEGATE:
http://mag.ncep.noaa.gov/GemPakTier/MagGemPakImag es /hwrf-nested/20120825/12/hwrf-nested_isaac09l_108_ mslp_10wnd.gif

Links not showing up.
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Certainly have some new convection firing N of Cuba's Eastern tip...
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Quoting FSUstormnut:
Isaac already starting to pop new convection near center ... lets see what happens over the next few hours.


he did but now seems to be interacting with cuba
Member Since: August 6, 2011 Posts: 0 Comments: 226
1342. GetReal
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Quoting justsouthofnola:


not working for me either
Yeah 72 hrs. should have came out by now.
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Euro isn't posting on RaleighWX site anymore... HMM
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1339. Seastep
Quoting dader:


I understand. It just seems like they could have waited until tonight/Sunday morning with the uncertainty. Closing schools has an incredible impact- especially for someone who has children in North Dade schools and I am expected to be at work for TS force winds- it's Florida not New England.


I generally agree with you. Broward (me) certainly shouldn't make the call until the 5pm tomorrow, imo.

Have to consider that the decision is county-wide, so take the SW most portion of Dade with schools. No school there, no school in Dade.
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Quoting SSideBrac:
I have to admit that I have an admiration (but would not like to live that way) for how the Cuban Authorities handle Evacuation- and they seem to do it comprehensively and effectively.
Thats because they have less beaurocratic tape to muddle thru..if the gov't issues an order..they do it!!..lol..
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Quoting GTcooliebai:
Is it me or did Euro stop running on Allan Huffman website?


not working for me either
Member Since: August 6, 2011 Posts: 0 Comments: 226
Isaac already starting to pop new convection near center ... lets see what happens over the next few hours.
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Quoting TropicalAnalystwx13:
ECMWF has a high-end Category 1 hurricane in 48 hours.

Too fast.
Member Since: August 1, 2012 Posts: 0 Comments: 246
1334. emcf30
Houston, we have a problem with Keeps post, methinks
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Quoting Allan012:
Its moving west according to Vis Sat.


your eye's are tricking you in fact he jogging north
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1332. KEEPEROFTHEGATE (Mod)
FINAL 120 HR

Member Since: July 15, 2006 Posts: 169 Comments: 53308
Quoting KeyWestbeachcomber:
I did my Hurricane grocery shop at 11pm last night,beat the crowds who had earlier almost gutted the shelves.I spent 400.American..ALWAYS get sticker shock when I see the total...Well I am ready.I have a BIG bird cage outside that I will cover with a tarp... SO MY CONCERN is STORM SURGE..although I am about 8 ft above sea level here in Old Town.Can anyone give me some input at this time what to expect.Wilma (though a different animal) had the north end of the Island under 5-6 ft of storm surge sea water TWICE during 2 high tides.It was much worse up the keys.Is this likely to happen again? I had never seen it in my 25 years here and really don't want to see it again. Input most appreciated THANK YOU FOR YOUR CONCIDERATION.
Smart of you to have stocked up ahead of the storm, especially in the Keys.
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1330. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53308
1329. 2ifbyC
Quoting oakland:


I'm sitting in Bradenton. Not a laughing matter for me.


Same here! Twix Manatee Ave and Blake...
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Product: Air Force Tropical RECCO Message (URNT11 KNHC)
Transmitted: 25th day of the month at 17:59Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number: 09
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 16
Observation Number: 03

Mandatory Data...

Observation Time: Saturday, 18:00Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 21.0N 70.5W
Location: 52 miles (84 km) to the SE (128°) from Cockburn Town, Turks and Caicos Islands (GBR).
Turbulence: Light
Conditions Along Flight Route: In the clear
Pressure Altitude: 6,710 meters
Flight Level Wind: From 120° at 29 knots (From the ESE at ~ 33.3 mph)
- The above is a spot wind.
- Winds were obtained using doppler radar or inertial systems.
Flight Level Temperature: -13°C
Flight Level Dew Point: -15°C
Weather (within 30 nautical miles): Overcast / Undercast
D-value: 35 geopotential meters

Remarks Section...

Surface Wind Speed (likely by SFMR): 36 knots (~ 41.4mph)
Member Since: April 29, 2007 Posts: 0 Comments: 7724
1327. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53308
1326. tfc3rid
Hi all, been lurking for years but finally posting... You all are doing an excellent job in followingthe storm and the models... Tremendous...

I'm in the Atlanta Metro area and we are prepping for about 8 to 10 inches (maybe even more) of rain here... Could be on the East side of a landfalling major hurricane up here...
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look how isaac seems to follow the moisture in front of him...
Member Since: August 6, 2011 Posts: 0 Comments: 226
1323. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53308
Is it me or did Euro stop running on Allan Huffman website?
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1321. KEEPEROFTHEGATE (Mod)
.
Member Since: July 15, 2006 Posts: 169 Comments: 53308

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.