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 Drakoen:
They are finding southwest winds north of the NHC coordinates... what a mess.


Does appear to be a developing LLC @ 22.3W 75.8N or minion circulation.
Member Since: August 19, 2005 Posts: 5 Comments: 5039
Isaac seems to be moving faster than expected. At the 12 hour mark, or at 0z tonight, he was supposed to be in his current location on the GFS. He is moving.
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2368. RevInFL
Well in light of another shift West at 5pm. I have decided to leave for my planned trip to the panhandle. Glad the Space Coast is once again escaping. Everyone here seems to think a further shift West will happen so I am feeling pretty confident. I am enjoying following all the discussion.
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Quoting Civicane49:
CAPTION: OM NOM NOM
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Quoting wunderkidcayman:
you know I notcied something Isaac really love cuba


I wounder though what would happen if the COC/eye just starts to shoot W soon

not saying it will or it won't but just what if

ok the low to SW kinda elongated W-E and Ridge to its NE and the weakness off the US E Coast is steering it so what if that low to the SW dips S and becomes ENE-WSW elongated the ridge builds inWward and the weakness lift N then what


Keep it coming... doing a great job entertaining me!
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2364. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
What the *use your imagination*?

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting Drakoen:
They are finding southwest winds north of the NHC coordinates... what a mess.


looks like they found the center, .2N and .2W of the 5pm

21:14:00Z 21.483N 76.267W 842.9 mb
(~ 24.89 inHg) 1,474 meters
(~ 4,836 feet) 997.9 mb
(~ 29.47 inHg) - From 57 at 0 knots
(From the ENE at ~ 0.0 mph)
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Local NWS notes that the Tampa Bay area will be in a strong pressure gradient between Isaac and the high, therefore winds will be quite robust in the area even if it passes a decent distance to our west.
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you know I notcied something Isaac really love cuba


I wounder though what would happen if the COC/eye just starts to shoot W soon

not saying it will or it won't but just what if

ok the low to SW kinda elongated W-E and Ridge to its NE and the weakness off the US E Coast is steering it so what if that low to the SW dips S and becomes ENE-WSW elongated the ridge builds inWward and the weakness lift N then what
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Quoting RTSplayer:
The surface low near Grand Cayman is about 3/4ths closed still, but convection there is intensifying on funktop.

There's a piece of ULL centered a couple hundred miles SSW of there which may be enhancing it.

Further, it looks like there may be a mid-level circulation forming as well.

Why isn't this showing up on any of the models except the NAM?!?


We started the day off here with moderate winds from due north, has switched to North-West since about midday,very slight wind about 10 mph now
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24Aug.06pmGMT: 16.7n71.3w (312.8*NWest@11.8knots) 55knots , 995millibars, TS
25Aug.12amGMT: 17.3n72.0w (311.8*NWest @ 9.0knots) 55knots , 992millibars, TS
25Aug.06amGMT: 18.1n72.7w (320.1*NWest@14.0knots) 55knots , 991millibars, TS
25Aug.12pmGMT's numbers are below, before 25Aug.6pmGMT's
Derived from NHC_ATCF data for TropicalStormIsaac for 25August6pmGMT
MinimumPressure increased from 998millibars to 1000millibars
MaxSusWinds decreased from 50knots(58mph)93km/h to 45knots(52mph)83km/h
Vector changed from 327.0*NWest@21.9mph(35.3km/h) to 308.1*NWest@20.6mph(33.1km/h)

CCC-CayoCoco :: DCT-RaggedIsland :: IGA-GreatInagua :: MOA-Moa :: BCA-Baracoa :: JAK-Jacmel

The southeasternmost dot on the longest line is TS.Isaac's most recent position

The longest line is a straightline projection through TS.Isaac's 2 most recent positions to its closest approach (within 18miles or 29kilometres) to a coastline
24Aug.6pmGMT: TS.Isaac was had been headed for passage over Cotes-de-Fer, 18miles(29kilometres)South of Miragoane (right, blob left of JAK)
25Aug.12amGMT: TS.Isaac had been for passage over Coates-de-Fer (left,blob left of JAK)
25Aug.6amGMT: TS.Isaac had been headed for passage over Cajobabo,Cuba (left,nearBCAdumbbell)
Between 6:13am and 6:25am GMT, TS.Isaac made landfall on Bainet,Haiti
25Aug.12pmGMT: TS.Isaac had been headed for a 1:50pmGMT landfall on Punta de Maisi (right,nearBCAdumbbell) and had been headed for passage 8.2miles(13.1kilometres)NEast of DuncanTown,RaggedIsland,Bahamas
25Aug.2pmGMT: TS.Isaac made landfall on PuntaCaleta,Cuba
25Aug.6pmGMT: TS.Isaac was heading for passage over (MTH)Marathon,Florida in ~19hours from now (when this was posted)

Copy&paste hav, dct-22.152n75.691w-22.219n75.586w, iga, ccc, moa, 20.067n74.461w-20.189n74.139w, bca, 18.175n72.987w-18.182n73.042w, jak, 18.1n72.7w-19.7n73.8w, 19.7n73.8w-20.8n75.3w, mth, 19.7n73.8w-24.722n81.015w, 19.7n73.8w-20.066n74.295w into the GreatCircleMapper for a larger map and other information
The previous mapping for comparison
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Quoting Drakoen:
They are finding southwest winds north of the NHC coordinates... what a mess.
could the center be relocating ???
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Quoting BahaHurican:


Afternoon everybody.

Looking at the big picture... what are the odds Isaac can pull that moisture towards him it as it heads NW?

This is a whopper of asystem...

It looks that way...but in my view this is Isaac and his new neighbor (new system) to his west...theory in post 2340...
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Quoting spathy:
Well I should have nothing to worry about. Or they missed a spot (Lee County Fl)Fort Myers.

LOL

you are under a Tropical storm watch
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2352. Drakoen
They are finding southwest winds north of the NHC coordinates... what a mess.
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convection is begining to build on the east side of Isaac tonight is going to be intresting
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Quoting louisianaboy444:
This is the first time I seen GFS ensembles this far west...Plenty even going into Louisiana

Image and video hosting by TinyPic


I guess I'm just a little confused. Isn't this the Model that has all the data in it? Why is LA. out of the cone.
After reading the discussion at 5, I'm going to wait until Monday to see how everything sets ups.
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Quoting NCHurricane2009:


I still vote for a slight rightward bias in track...because of this system you point out. I find it interesting this new system west of Isaac has been producing a very persistent burst of clouds in the Florida Straits since 12 hrs ago...pretty cool....

At the upper-levels...this system is getting split in half...into one ULL in the W Carib...another ULL over the Carolinas...the split driven by Isaac's massive ULAC. Mabye ULL over the Carolinas is too far north to influence Isaac's track...but the W Carib ULL may help continue the more poleward Isaac track.

Plus Isaac is now in the east side of a broad surface low pressure field extending into the W Carib. This new surface low pressure field has been generated by split flow upper divergence between Isaac's ULAC...W Carib ULL...and Carolinas ULL. Cyclonic flow on the east side of the surface low pressure field may also help a more poleward track for Isaac....

You're over-analyzing.
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Is it possible for Issac to grab that big glob in front of it and wrap it up. Its kind of in the way so I was wondering since he is so big a storm is that possible?
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Pressure quite low here today 1004mb.
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2345. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting breald:
Good afternoon everyone. Things are starting to get interesting for Florida. I say Isaac will shift to the east. But that is my uneducated guess.


Yup 18z models have been over playing the High from yesterday expect some type of eastern shift in the 11pm cone. next models should be much more accurate.
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Ominous.

IT SHOULD BE NOTED THAT THE GLOBAL MODELS ARE
FORECASTING A VERY FAVORABLE PATTERN OF UPPER-LEVEL WINDS OVER THE
NORTHERN GULF OF MEXICO BY 72 HR. SHOULD THIS VERIFY AND SHOULD
ISAAC ESTABLISH AN INNER CORE...THE CYCLONE COULD BE SIGNIFICANTLY
STRONGER THAN CURRENTLY FORECAST.
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I got a very tough question for anyone who might have the answer! When was the last time a storm skirted Cuba (Like Isaac) and then hit the Florida Panhandle as a Moderate to strong Hurricane? I can't think of one recently if there even ever was one; maybe if you can't find one then it is unlikely Isaac will do the same???
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Quoting RTSplayer:
The surface low near Grand Cayman is about 3/4ths closed still, but convection there is intensifying on funktop.

There's a piece of ULL centered a couple hundred miles SSW of there which may be enhancing it.

Further, it looks like there may be a mid-level circulation forming as well.

Why isn't this showing up on any of the models except the NAM?!?


I still vote for a slight rightward bias in track...because of this system you point out. I find it interesting this new system west of Isaac has been producing a very persistent burst of clouds in the Florida Straits since 12 hrs ago...pretty cool....

At the upper-levels...this system is getting split in half...into one ULL in the W Carib...another ULL over the Carolinas...the split driven by Isaac's massive ULAC. Mabye ULL over the Carolinas is too far north to influence Isaac's track...but the W Carib ULL may help continue the more poleward Isaac track.

Plus Isaac is now in the east side of a broad surface low pressure field extending into the W Carib. This new surface low pressure field has been generated by split flow upper divergence between Isaac's ULAC...W Carib ULL...and Carolinas ULL. Cyclonic flow on the east side of the surface low pressure field may also help a more poleward track for Isaac....
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Baha



afternoon... the only nasty squall we had was the one at 4:50 this morning
hardly any rain since... windy yes
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get your shutters up in s fla....its going thru Key Largo///NHC is to hell bent on west...which it aint going
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2337. KEEPEROFTHEGATE (Mod)
Quoting Grothar:
Moving much faster than earlier.


when the nightfalls
it will get up too dance
Member Since: July 15, 2006 Posts: 169 Comments: 53296
2336. mfcmom
Any guesses on Panama City impact yet, looks to have pulled a little west? Thank you.
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That NHC discussion made me nauseous. Seriously ill. Holy cow. Will continue with our preparations. Nothing like telling your son that we need to celebrate his 16th birthday tonight as we will probably be to involved in hurricane prep tomorrow.
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They're looking hard.

211430 2130N 07618W 8430 01472 9977 +186 +155 072003 004 /// /// 03
Member Since: September 2, 2009 Posts: 130 Comments: 21091


Can anyone tell if they see a fix from Recon or Obs that suggest a center as close as they are flying to the NE Cuban coast!
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The Latest
(click to enlarge)


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Quoting BahaHurican:


Afternoon everybody.

Looking at the big picture... what are the odds Isaac can pull that moisture towards him it as it heads NW?

This is a whopper of asystem...
I was wondering about that too. What if it pulls all that moisture together and becomes one massive system?
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2330. Bielle
Any word (official or otherwise) about the Bahamas and the other islands north of the COC?
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Quoting Hurricanes305:


Impossible 97 degree SST OMG thats cant be possible.
i meant 87 hit the wrong button
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Quoting BahaHurican:


Afternoon everybody.

Looking at the big picture... what are the odds Isaac can pull that moisture towards him it as it heads NW?

This is a whopper of asystem...

They already are.
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NHC track seems very reasonable to me right now, if anything I would forecast Isaac to go slightly west of their placement... The panhandle of FL seems like a good bet though.
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I have sein any one so hell bent on n coast of cuba...since they said it was going to texas..and went north

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fowey rock just east of key biscayne,fl


Conditions at FWYF1 as of
(4:00 pm EDT)
2000 GMT on 08/25/2012:
Unit of Measure: Time Zone:

Click on the graph icon in the table below to see a time series plot of the last five days of that observation.
5-day plot - Wind Direction Wind Direction (WDIR): NE ( 50 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 22 kts
5-day plot - Wind Gust Wind Gust (GST): 25 kts
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.88 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.06 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 84.7 °F
5-day plot - Water Temperature Water Temperature (WTMP): 84.2 °F
5-day plot - Wind Speed at 10 Meters Wind Speed at 10 meters (WSPD10M): 19 kts
5-day plot - Wind Speed at 10 Meters Wind Speed at 20 meters (WSPD20M): 19 kts
5-day plot - Wind Speed, Wind Gust and Atmospheric Pressure Combined plot of Wind Speed, Gust, and Air Pressure
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New center fix is pretty good, and would be hard to screw up at this point, with HH, Radar, and Shortwave all agreeing very closely.




Still 3.5 days out, so that gives time for one more Euro to complete and 2 more GFS before the 3 day cone is published for the N. Gulf coast. Hopefully they'll all be good, reliable runs with good initialization.


If I was in the keys, I'd assume Cat 1 minimum.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting CybrTeddy:
Faster Isaac goes the quicker it gets away from Cuba, forecasted to slow down some as well once in the Gulf.


Its moving quicker because it wants to align itself with
the stronger convection. Hurricane at 11pm looking more likely.
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Quoting BahaHurican:


Afternoon everybody.

Looking at the big picture... what are the odds Isaac can pull that moisture towards him it as it heads NW?

This is a whopper of asystem...


Looks like that is exactly what Isaac is starting to do.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
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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.