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 MiamiHurricanes09:
I agree.


I respectfully disagree. He is already on the southern edge of the NHC cone right now.
Just onshore in Cuba.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1719. Levi32
Quoting MississippiWx:
These interpolated model plots are fooling you guys, I think. When has the GFS not shown that Isaac would pop out on the NE Cuban coast? For that matter, the GFDL/HWRF, amongst other models, have shown that the entire time as well. I don't recall many actual model runs (not spaghetti plots) showing a straight line path like that.





I don't know what you mean by "interpolated," but those plot points are at the coordinates of the low pressure center depicted by each model.

The interpolation that occurs on those plots is simply an update of the coordinates during the early model cycles when the late models have not yet updated. During that time, the previous model run is interpolated given the new position of the cyclone. The "interpolated" track is really the same track but given a new initial position. That's why you see "AVNI" for "AVN interpolated from the previous run" during the first couple of hours after a model cycle. The real GFS 12z has not come out yet on that map.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Isaac has not weakened at all today. The winds remain at 60 mph and the pressure looks to be around 997 millibars.
Member Since: July 6, 2010 Posts: 113 Comments: 32531
Issac is definitely still a 50kt cyclone; pressure is also sub-999mb.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting JasonRE:

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?


Me to, I started in 2004 when a friend told me about WU, love this season & live tracking, wake up all hours of the night checking, and now I check with my phone,,, do the words ADDICTION mean anything
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Quoting 954FtLCane:
Sorry for the off topic post.

Astronaut Neil Armstrong has passed away.

82 yrs old, 1930-2012

RIP


What a loss. The end of an era. Sadness.
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from local media:

Miami-Dade Mayor Carlos Gimenez said tropical storm force winds from Isaac could begin in South Florida as early as Sunday morning.

He urged residents to begin putting up their shutters, gather supplies and fill up their cars with gas.

"You should begin putting up your shutters now. Even tropical storm winds can cause damage so you shouldn’t wait until the last moment to protect your home," he said.

Miami International Airport will remain open but some airlines could decide to cancel certain flights, Gimenez said.

Meanwhile, public schools in Miami-Dade and Broward County were canceled Monday.

"Things have changed in the last less than 24 hours, we thought we were going to be in a much better situation, things have shifted to the right and to the east, and we may have a hurricane instead of just a tropical storm," Gimenez said.

He said residents should have food and water for three days, secure outside furniture and stay alert to the latest storm developments.

Broward County will also open homeless shelters and buses were picking up people at designateed locations. They are the Broward Outreach Center at 2056 Scott Street in Hollywood, Pompano Beach City Hall on Atlantic Boulevard and First Avenue and at the Salvation Army Lodge at 1445 West Broward Boulevard in Fort Lauderdale.

The National Weather Service and the National Hurricane Center meanwhile, are busy forecasting Isaac and encouraging South Florida residents to take preparations ahead of the storm
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Quoting louisianaboy444:
This is the first time I seen GFS ensembles this far west...Plenty even going into Louisiana

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While I really don't want Issac going over my son in FWB, especially as he is tasked to ride it out there, I do not want it in Louisiana. Sigh, there is no real place I want it to hit except for the impossible ones like out to sea.
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Lol Taz you do make me laugh Blog wouldn't be the same without you.

Just got back from wally world got all my supply's in should be a rough ride here on marco if we get the dirty side of Isaac.
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1709. angiest
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


One all the way out on Bolivar.
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recon found

999.2 mb
(~ 29.51 inHg
Member Since: May 21, 2006 Posts: 5091 Comments: 115362
The latest CIMSS vorticity analysis shows Isaac as being a little tilted S and SE-erly as heights increase, matching what we see with its satellite presentation. But it's not horrible and if he can pull away from the Cuban coast a little this evening he has plenty of opportunity to reorganize and try to build an eyewall again.

850 and 700 mb levels



500 mb

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its offshore
Member Since: July 21, 2010 Posts: 0 Comments: 1181
Quoting Hurricanes101:
I think the track will be on the eastern side of the guidance, due to the fact that I think Isaac will be stronger than forecast and therefore will turn north sooner
I agree.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Neil Armstrong has died. I hope we soon resume our space program and find ourselves as a nation walking on the moon and beyond. Rest In Peace.
Member Since: August 1, 2007 Posts: 0 Comments: 201
S. FL is under 8/10 TORCON according to Dr. Greg Forbes on TWC.

Please folks be careful as Isaac heads to the west of you.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1702. Michfan
Quoting GetReal:
The center is clearly visible on this site loop...

Link


Can you pm me the link to get those loops. I'm having trouble finding it in my favorites. Used to have a perfect Rapid Scan site but lost it all in my format.
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999.2 Minimum pressure so far. but last of the group, so could be lower.
Member Since: September 5, 2008 Posts: 0 Comments: 125
Quoting hurricanejunky:


Yeah when zoomed in...the COC is still a little tricky almost like vertical stacking is still not quite perfect.

Definitely, food convection with COC or AOC (area of circulation) especially in NE quad. Any thoughts on how Isaac will react to the FL mess??
Member Since: August 1, 2012 Posts: 0 Comments: 269
1698. GetReal
CMC 12z 96 hours


I'm not buying this model... But being fair to the CMC fans...
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Quoting tennisgirl08:


Dr. Rick Knabb on TWC just said it is onshore.


That's because it moved west back over land.

It was definitely over water a few frames ago.

visible floater



Will probably wobble on and off the coast till it gets around where Cuba topography curves away to the west away from the average track forecast.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
1694. HCW
Forecast track: Focus On The Forecast Uncertainty Cone Issac Has a 1 and 3 chance of being outside this cone
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Time: 19:14:30Z
Coordinates: 21.3N 75.4167W
Acft. Static Air Press: 843.4 mb (~ 24.91 inHg)
Acft. Geopotential Hgt: 1,474 meters (~ 4,836 feet)
Extrap. Sfc. Press: 999.2 mb (~ 29.51 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 120° at 35 knots (From the ESE at ~ 40.2 mph)
Air Temp: 17.0°C* (~ 62.6°F*)
Dew Pt: 17.0°C* (~ 62.6°F*)
Peak (10s) Flt. Lvl. Wind: 36 knots (~ 41.4 mph)
SFMR Peak (10s) Sfc. Wind: 45 knots* (~ 51.7 mph*)
SFMR Rain Rate: 8 mm/hr* (~ 0.31 in/hr*)
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The wishcasters are riled
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These interpolated model plots are fooling you guys, I think. When has the GFS not shown that Isaac would pop out on the NE Cuban coast? For that matter, the GFDL/HWRF, amongst other models, have shown that the entire time as well. I don't recall many actual model runs (not spaghetti plots) showing a straight line path like that.



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This is the first time I seen GFS ensembles this far west...Plenty even going into Louisiana

Image and video hosting by TinyPic
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Quoting atmosweather:


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


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.
Thanks a ton guys.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
I think the track will be on the eastern side of the guidance, due to the fact that I think Isaac will be stronger than forecast and therefore will turn north sooner
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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.


Euro got the same data.
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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 worried, but watching closely.
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1684. GetReal
The center is clearly visible on this site loop...

Link
Member Since: July 4, 2005 Posts: 204 Comments: 8898
1683. Drakoen
The EURO shows sustained minimal tropical storm force winds across south Florida. This higher winds up to hurricane force will probably get contained within the convection closer to the center as the system gets better organized.
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I think Isaac is onshore Cuba around 20.5N/76W , just my take though.
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12z GFS and ECMWF are actually pretty similar out to 48hrs. Both show pretty similar track and intensity. Beyond that point, however, the ECMWF deepens the storm more and shows a greater weakness in the ridge to the north.
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Is Isaac heading West or Northwest?
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Quoting weatherh98:


wait or the vortex message


Am waiting - but the wind direction has me confused - if the forecast points are correct - HH should be reporting easterly winds - Perhaps the wind field exists without convection.
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Quoting reedzone:
FINALLY the EURO makes sense!


It has made sense all along.
Member Since: July 6, 2010 Posts: 113 Comments: 32531
Quoting clwstmchasr:
Is it just me, or has the NHC track guidance been really good so far.


Real good.

It generally is.

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Isaac will be dangerous if he can get the moisture left over South Florida from the trough into his circulation! Big storm trying to become Massive!
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Quoting RobbWilder:


Just announced closed monday for broward schools.



Thanks for the update and I apologize to that other blogger... the WSVN had not updated their info..


I did go to the broward county school website and they have decided to close Monday.


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Quoting Levi32:


The foundation of science is doubt.

Isaac is completely outside the 24-hour supercomputer guidance envelope from yesterday (see below). There is more than enough room to question computer forecasts, always. That's why the NHC exists, and other human forecasters have jobs.



Correct. Models are not the foundation of science. Models are a result OF science. They are only as good as the research and data you feed them. And since we don't have meter resolution data to enter into the models (nor do we have the computation power to run models at that resolution), there will ALWAYS be errors.

Models are used for guidance. They are not and cannot be perfect. This is why we rely on experts in the field to interpret the results and combine it with other information and experience to make intelligent predictions.
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Quoting reedzone:
FINALLY the EURO makes sense!



Meanwhile, the GFS continues on a western rampage. LOL
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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.