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 weatherh98:


look at the date


You look at the date: Aug. 25 2012 18 UTC
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Based on the winds that the HH are reporting - center is further north than the forecast points. I am looking at this incorrectly?
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Quoting hurricanejunky:


Did I see a couple of hot towers in there to the NE of the COC?

I did
Member Since: August 1, 2012 Posts: 0 Comments: 269
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.

Indeed, humans are more than capable of beating the super computers.

Here were the model forecast when I made my forecast:




And here's my forecast from about the same time:




Admittedly, Isaac spent even less time over Cuba than I expected, but I did do better than the models (so far).
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Looks like they went south of the center.
Member Since: July 8, 2005 Posts: 259 Comments: 24508
Quoting Seflhurricane:
if Isaac jogs to the east or north it will be over open water

It IS over water
Member Since: August 1, 2012 Posts: 0 Comments: 269
Quoting Drakoen:
Looks like he is riding the coastline at the moment.
RAMSDIS zoomed loop


Did I see a couple of hot towers in there to the NE of the COC?
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Quoting weatherh98:


i dont care for him much dumbs it down too much


Which is a good think in my book as the general public will understand.
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Quoting TomballTXPride:


They are all not in agreement with how much of an effect Cuba will have on the system or not, which will have far reaches ramifications down the road one way or another.

I foresee a dramatic tightening of the model cluster after it moves at least 50 miles away from the landmass and approaches the Keys.


I think it has more to do with the ridge and trough than its interaction with Cuba.

Member Since: July 17, 2008 Posts: 0 Comments: 1242
Quoting ncstorm:
dannngg..the euro shifted east big time..



link?
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Sub 920? Well Joe B. has been hyping a big strong storm for days now. Seemed like rating hype at the time, not so much now. The three storms he names as a blend give one great pause. The analogs Jeff used yesterday gave a little hint too at possible big time problems. When I saw Isaac's storms used as an analog to Isaac I thought Jeff was thinking this could be epic.
Member Since: April 18, 2012 Posts: 0 Comments: 2437
1609. Drakoen
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.



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.
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Is there an update yet to Isaac's diameter?

Thanks
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Quoting CybrTeddy:
Non contaminated 63mph winds, so Isaac hasn't weakened at all.
55 knots
(~ 63.2 mph)

And the rain rates for it as well are low.
12 mm/hr
(~ 0.47 in/hr)

What about the lower flight level winds?
Member Since: July 6, 2010 Posts: 113 Comments: 32558
Nrt, if you're around, how many dropsondes made it into the 12z GFS?
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Quoting Maineweatherguy20023:

59 actually

Time: 18:54:00Z
Coordinates: 20.65N 74.3167W
Acft. Static Air Press: 843.5 mb (~ 24.91 inHg)
Acft. Geopotential Hgt: 1,535 meters (~ 5,036 feet)
Extrap. Sfc. Press: 1006.6 mb (~ 29.72 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 199� at 33 knots (From the SSW at ~ 37.9 mph)
Air Temp: 16.0�C* (~ 60.8�F*)
Dew Pt: 16.0�C* (~ 60.8�F*)
Peak (10s) Flt. Lvl. Wind: 36 knots (~ 41.4 mph)
SFMR Peak (10s) Sfc. Wind: 52 knots (~ 59.8 mph)
SFMR Rain Rate: 12 mm/hr (~ 0.47 in/hr)
(*) Denotes suspect data

BTW NOT Contaminated


SFMR is broken, every reading is over flight level wind speed, some by as much as 50%.
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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.



also heading more westerly than predicted.

did u post a blog today? havent checked my email
Member Since: June 17, 2011 Posts: 11 Comments: 6539
Quoting Tribucanes:
Percentage that the RNC gets postponed gotta be pushing 20% at this point. So much for 0.2% chance just a week ago. What will they do if it's postponed and flooding makes the site unusable? Anyone know where it's planned to move to if necessary?

There are no backup plans to move it. The delegates would still vote by phone according to the radio program I was listening to.
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Non contaminated 63mph winds, so Isaac hasn't weakened at all.
55 knots
(~ 63.2 mph)

And the rain rates for it as well are low.
12 mm/hr
(~ 0.47 in/hr)
Member Since: July 8, 2005 Posts: 259 Comments: 24508
Quoting cchsweatherman:


Pretty much am maintaining that South Floridians and residents in the Keys should be prepared for hurricane conditions starting tomorrow evening and going into the early morning hours Monday.

Over the past 24 hours or so, this storm has had a tendency to go further north and east than the forecasters and computer models expected, so it would not surprise me to see Tropical Storm Isaac continue its current trend pulling away from Cuba and off in a general NW direction over the next 12 hours or so. Convection seems to be slowly, but surely rebuilding near and over the circulation center as Isaac recovers from its encounters with Haiti and Cuba.




TY we have fools here who think his center is still onshore
Member Since: July 21, 2010 Posts: 0 Comments: 1181
They cancelled school here as school let out, about ten hours before Rita hit us. Announced no school and to not try to evacuate unless we wanted to be in our cars on the road when she hit.
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Anyone think Kirk will be here before September?
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As we get neared to sunset, expect thunderstorm activity over eastern Cuba and Hispañola to explode.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1596. Levi32
Quoting robj144:


Yup, as they always almost do... look at Ernesto. I love how so many here doubt the ability of Ph. D's, sophisticated computer models, and supercomputers. I understand though, this is a blog and it's all in fun, but it still amazes me.


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.

Member Since: November 24, 2005 Posts: 635 Comments: 26686
Quoting MAweatherboy1:

I'm already wrong, lol, I said they'd find 50mph winds and they've already found 57.


All the SFMR data is going to be thrown out for this mission, the measurements are clearly unrepresentative of the proper winds down at the surface. Maximum flight level winds have barely touched 45 kts yet there are multiple readings from the SFMR of over 50 kts at the surface.
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1594. dmh1026
Quoting Yelladawg:


Collier School Board said to be waiting until 5 PM tomorrow to make announcement. Nothing like waiting until the last minute...
That is very late in the game!!!
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Quoting WPBHurricane05:


PBC schools will be closed tomorrow!!!!


I would hope they wouldnt be open on a Sunday! lol
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Quoting MAweatherboy1:

I'm already wrong, lol, I said they'd find 50mph winds and they've already found 57.

59 actually

Time: 18:54:00Z
Coordinates: 20.65N 74.3167W
Acft. Static Air Press: 843.5 mb (~ 24.91 inHg)
Acft. Geopotential Hgt: 1,535 meters (~ 5,036 feet)
Extrap. Sfc. Press: 1006.6 mb (~ 29.72 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 199 at 33 knots (From the SSW at ~ 37.9 mph)
Air Temp: 16.0C* (~ 60.8F*)
Dew Pt: 16.0C* (~ 60.8F*)
Peak (10s) Flt. Lvl. Wind: 36 knots (~ 41.4 mph)
SFMR Peak (10s) Sfc. Wind: 52 knots (~ 59.8 mph)
SFMR Rain Rate: 12 mm/hr (~ 0.47 in/hr)
(*) Denotes suspect data

BTW NOT Contaminated
Member Since: August 1, 2012 Posts: 0 Comments: 269
Well HH is now in Cuban airspace, so that answers that question.
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Quoting Seflhurricane:
he has been pretty good thus far but they have had the new guy talking the most


i dont care for him much dumbs it down too much
Member Since: June 17, 2011 Posts: 11 Comments: 6539
"K" and "L" playing tag near the east coast.



They came from different directions, and did not develop adjacent to one another, so this is possible, however ridiculous it seems.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
1588. Hhunter
Joe Bastardi...latest update...

There have been 2 Saturday where I changed tracks on storms based on the modeling I saw. Sep 11, 2004 I think was one, I was competing in the nationals in bodybuilding and changed a track on Ivan because of model support all in one camp ( they took it east of my idea that i had for over a week) and I bit. 12 hours later I changed it back to what I had. In spite of prety good result in the competition, I was sick over what I had done. The following year I held on to Rita to Galveston too long though to be fair, most tracks were south of mine 5 days before, caught up and went by me. But that was a case where moving Ivan was in my mind. The second time was recently with Debby,



Here is what is bugging me about all this. 1) The euro was plain bad on Debby and the same thing on Faye in 2008. The west nuclear option has had me keep that western window open, and the 1947 New Orleans threat situation is something that bothers me about all this too. I have posted on that.



But until I see how this looks tomorrow, I am not going to jump further than what I have now, which through the keys as an intensifying perhaps major hurricane by late tomorrow, then a track further east.



Not being stubborn. we can all see what this is capable of, but Sunday was always the day of decision as this is a fork in the road situation.

What the GFS has is the blend of Ivan, Camille, and Katrina on track and I think if this takes that path, we are looking at a sub 920 mb storm.


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Quoting Seflhurricane:
sure does but its over water


Looked to me that it was both over water and overland.
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Quoting WPBHurricane05:


PBC schools will be closed tomorrow!!!!

They sure will - it's Sunday - duh!
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Notice some convection forming over the center. Still a ton of work to do, but it's trying.

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1584. Michfan
Time: 18:54:30Z
Coordinates: 20.65N 74.35W
Acft. Static Air Press: 843.8 mb (~ 24.92 inHg)
Acft. Geopotential Hgt: 1,528 meters (~ 5,013 feet)
Extrap. Sfc. Press: 1006.0 mb (~ 29.71 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 187° at 33 knots (From the S at ~ 37.9 mph)
Air Temp: 16.7°C (~ 62.1°F)
Dew Pt: 16.7°C (~ 62.1°F)
Peak (10s) Flt. Lvl. Wind: 36 knots (~ 41.4 mph)
SFMR Peak (10s) Sfc. Wind: 52 knots (~ 59.8 mph)
SFMR Rain Rate: 12 mm/hr (~ 0.47 in/hr)
(*) Denotes suspect data

Recon now approaching the center.
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Quoting wpb:
do u have center over land


No I do not. I have the center just slightly off to the north and west of the last NHC position.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting dmh1026:

I suspect Lee will as of 5 PM advisory....


Collier School Board said to be waiting until 5 PM tomorrow to make announcement. Nothing like waiting until the last minute...
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Quoting washingtonian115:
I usually get a phone call first about the school being cancelled before it's posting on the school's site.


Yep, phone trees. Local radios and tv will generally have it out first, often faster than the phone trees as they are notified as soon as the Supt. makes the decision.
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1580. dmh1026
Oh oh...TWC is at Fort Myers Beach...Now I know we're doomed...Yikes!!!
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Quoting washingaway:


Just came out.


look at the date
Member Since: June 17, 2011 Posts: 11 Comments: 6539
if Isaac jogs to the east or north it will be over open water
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Percentage that the RNC gets postponed gotta be pushing 20% at this point. So much for 0.2% chance just a week ago. What will they do if it's postponed and flooding makes the site unusable? Anyone know where it's planned to move to if necessary?
Member Since: April 18, 2012 Posts: 0 Comments: 2437
1576. scott39
Looks like Isaac is taking a little bit of a beating on its COC. I also noticed to the N is 20 to 25mph vertical wind shear.
Member Since: June 13, 2009 Posts: 0 Comments: 6897
Quoting FLWeatherFreak91:
Old.


Just came out.
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1574. ncstorm
Quoting washingtonian115:
I usually get a phone call first about the school being cancelled before it's posting on the school's site.


Same here..
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Quoting Seflhurricane:
recon decending into the center

I'm already wrong, lol, I said they'd find 50mph winds and they've already found 57.
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Quoting weatherh98:
Wish bryan norcoss would inject some light on the current situation

lott guesscasting
he has been pretty good thus far but they have had the new guy talking the most
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1571. dmh1026
Quoting Yelladawg:


Collier Co. has been under a hurricane warning since this AM.

I suspect Lee will as of 5 PM advisory....
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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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