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 Tribucanes:


MOST??? of the people on the blog are wishcasting. I've seen posts like this over and over. I know this post got lots of pluses, ya'll must be reading a different blog than I; because I don't see that at all. People are excited by the models which bring the storm closest to them. Guess why? Because it well may. Saying they WANT to be hit by a monster Isaac is a very big leap. I'm sure someone will post something in an hour stating the same ridiculous thing because it'll get lots of pluses. I'm sure SOMEONE or two may WANT to get hit directly by a major. Rest assured MOST do not in any way.


Yes I am a Wish caster,,, I wish it stay away from LA,,,,
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Quoting Drakoen:
RAMSDIS 1 minute satellite imagery for the very latest.

Looks like it's offshore to me...
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Quoting MarcoIslandCat5:


Can't see that happening already convection is blooming in the NE quad.

sykkid is troll the more I see it! Saying this storm is done which it isn't!!!
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Quoting robj144:


Huh? There was no mention of "big business" anywhere in the post you quoted.
I messed up.......sorry
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Center has most likely just emerged offshore. Will be interesting to see if recon can get close enough.
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1966. 900MB
Quoting Romneybot5000x:


Ah wishful thinking


If you look at the long loop of the visible and follow it, I think you'll agree that the center is under the new convection at 21N.
Member Since: June 11, 2006 Posts: 0 Comments: 660
Quoting ITCZ:





His family is requesting that tonight in his honor we all wink at the moon :/
That is a very cool memorial..I will do that even though the moon probably won't be visible.... Very cool
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1964. robj144
Quoting PalmBeachWeather:
I guess I don't understand "big business" So tell me why MTV doesn't play music videos anymore?....LOL


Huh? There was no mention of "big business" anywhere in the post you quoted.
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Quoting SykKid:
im hope isaac die over cuba


Can't see that happening already convection is blooming in the NE quad.
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Quoting cajuncoon:
I cant understand why anyone would want a hurricane to come to them, its seems like most of the people on this blog are wishcasting, picking models because its closer to them, I lost everything when Katrina destroyed southern Plaquemines Parish, you all may love the weather as I do, but these storms are nothing to play with. God Bless


MOST??? of the people on the blog are wishcasting. I've seen posts like this over and over. I know this post got lots of pluses, ya'll must be reading a different blog than I; because I don't see that at all. People are excited by the models which bring the storm closest to them. Guess why? Because it well may. Saying they WANT to be hit by a monster Isaac is a very big leap. I'm sure someone will post something in an hour stating the same ridiculous thing because it'll get lots of pluses. I'm sure SOMEONE or two may WANT to get hit directly by a major. Rest assured MOST do not in any way.
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That's why people should be using carp and not cr!#p, keeps it weather related :)
Quoting Tazmanian:
i here by now call 97L a fish storm



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Quoting STXHurricanes2012:
Anyways back to Isaac...to me he's off the coast!


Ah wishful thinking
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1958. ITCZ
Quoting FatPenguin:
RIP, Neil Armstrong. Thank you for your service and going where no one has gone before.

I will always have that memory of being a little kid watching in total awe as you stepped onto the moon. It was one of the main reasons I was inspired to take a strong interest in the sciences.





His family is requesting that tonight in his honor we all wink at the moon :/
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1957. Drakoen
Quoting MiamiHurricanes09:
I don't know how you people like that satellite image. That angle is awful.


Did you look at my link and not the one Levi posted?
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Just about 30 minutes ago we had a band roll through Little Exuma here in the central Bahamas that had 60mph gusts in it. Pressure dropped to 1002mb
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Quoting STXHurricanes2012:

So the C word isn't foul language? Very clear it is. Remember this blog is strict with this especially with Isaac out there right now!


All I said was this halibut was fit for Jehovah!

Everything about this storm says trouble...
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Quoting Drakoen:


That's what i'm waiting for- to see how Issac interacts with a region of abundant moisture. Whether or not it can wrap that convection into its own spin coupled with the increase TCHP values it will be encountering. Needs to pull away from Hispaniola and Cuba some more to really take off.
..
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Quoting Hurricanes101:
To me the rapid scan clearly shows Isaac is offshore
I don't know how you people like that satellite image. That angle is awful.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
The intensity of Isaac and rate of intensification will help determine the track

A stronger Isaac will likely turn north sooner and therefore be more to the east...likewise a weaker Isaac will likely follow the track or even move west of it
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Look how the NE has filled out in just a few hours.



S. Side is redeveloping some scattered storms which are probably going to form new feeder bands soon.
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Quoting MississippiWx:
The super rapid scan visible loops show that the center is inland. It will pop back out over water since it is just over a point that juts out. If it keeps its current heading, it will parallel the coastline for a while.

No, they don't. The center is just offshore.
Member Since: July 6, 2010 Posts: 113 Comments: 31456
Recon is only allowed to get a certain distance from the coast of Cuba. Probably won't get a center fix again this time.
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Quoting PalmBeachWeather:
Are you my bf? Is this your handle?


I don't have a girlfriend at the moment LOL
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Quoting Tazmanian:
i here by now call 97L a fish storm


An historical day ! Taz SEES a fish storm. Will wonders ever cease. lol
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Quoting PalmBeachWeather:
Actually the weather in Palm Beach county is very nice at the time... Very light winds, no rain, not too hot.... Early this morning the thunderstorms and lightning were wicked...


yup, i'm just about to go to the pool and do some laps.
Member Since: August 4, 2011 Posts: 0 Comments: 288
Quoting flcanes:

it is not decoupled


ok
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To me the rapid scan clearly shows Isaac is offshore
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On the Tropical update on TWC they zoomed in on a excellent sat image and it showed Isaac's center just off the North coast of Cuba.
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Quoting angiest:
From the Houston forecast discussion at 4:30 this morning.

TOMORROW MEAN SFC-700MB RIDGING MOVES NORTH TAPERING OFF THE
MOISTURE TAP. GFS SPLITS A PIECE OF THE UPPER TROUGH NOW OVER THE
TX PANHANDLE TO OUR WEST TOMORROW SO CANNOT RULE OUT PCPN CHANCES
BUT THEY ARE LOWER THAN TODAY. BY MONDAY ISAAC IS FORECAST BY NHC
TO BE IN THE FAR EASTERN GULF. THIS PUTS SE TX IN A GENERALLY DEEP
OFFSHORE FLOW REGIME. INTERESTING FLIES IN THE OINTMENT FOR
TUESDAY IS A WESTERLY MOVING 250MB LOW THAT BREAKS OFF THE TROUGH
NOW IN THE SOUTHEASTERN US AND SOME RELATIVELY HIGH PWAT AIR ALONG
AND AHEAD OF A FRONTAL ZONE TO OUR NORTH. ECM/GFS MOS POPS ARE
QUITE HIGH ON TUESDAY (40 TO NEAR 50 PERCENT) BUT GIVEN THE USUAL
PATTERN OFF TO THE NORTHWEST OF TROPICAL SYSTEMS IN THE GULF THIS
PCPN CHANCE SEEMS HIGH SO WILL COMPROMISE BY LEAVING OUR 20
PERCENT FORECAST IN PLACE.
WILL NEED TO CONTINUE TO MONITOR THIS
AS TUESDAY COULD BE BRIEFLY WETTER. WED THOUGH THE NEXT WEEKEND
LOOK VERY DRY AND TEMPERATURES WILL BE WARMING. GFS ENSEMBLE MEAN
MOS IS HIGHER THAN GFS LONG RANGE MOS (MEX) AND THE EXPERIMENTAL
ECM MOS IS EVEN HIGHER. AS A RESULT MAX TEMPS ON THU-FRI WERE
INCREASED.


It seems like there is something interesting in the bolded part, but I'm not sure what to make of it.


What's weird to me about it is I would think a gulf storm to our east would bring us a dry NE wind. Unless he's so big we'd catch the outer rains from him? He'd have to be really big. But what do I know? :)
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1939. Drakoen
Quoting tennisgirl08:


Drak - do you see that mass of convection caused by the low pressure ahead of Isaac? On the upper NW side of the satellite link you posted?

What will happen when Isaac interacts with that?

I haven't seen many people discuss this on the blog today.


That's what i'm waiting for- to see how Issac interacts with a region of abundant moisture. Whether or not it can wrap that convection into its own spin coupled with the increase TCHP values it will be encountering. Needs to pull away from Hispaniola and Cuba some more to really take off.
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Quoting PalmBeachWeather:
I thought I would tune into TWC and see what the other "experts" had to say about Isaac.... They had a freekin' ad about one of their upcoming shows.."Iron Men" about steel workers on skyscrapers... What the freekin" heck does that have to do with weather....GeeeZ


Do you understand they have to keep ratings in order to maintain advertisement income?

They can't just forecast local on the 8s all day and expect people to watch even with its fair skies or something, so they have to do other things to get viewers.

What does it have to do with weather?

Not much, but if they didn't make money they couldn't do the weather anyway...
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hahhahahahah...what-ev. Even my bible-thumpin' best friend from Kansas says CRAP.
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Anything before Isaac re intensifies off the coast of Cuba is just a low confidence guess IMO. I am sticking to my guns which is with the NHC between Pcola and Panama beach FL.
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Quoting FatPenguin:
RIP, Neil Armstrong. Thank you for your service and going where no one has gone before.

I will always have that memory of being a little kid watching in total awe as you stepped onto the moon. It was one of the main reasons I was inspired to take a strong interest in the sciences.


An era is gone.
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Actually the weather in Palm Beach county is very nice at the time... Very light winds, no rain, not too hot.... Early this morning the thunderstorms and lightning were wicked...
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Wow...just getting back on from this morning...looks like GFS shifted to the west again??!! I don't think anyone knows what this storm is gonna do...I would say from Lake Charles, La. to Fl.panhandle should be watching this one...
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Quoting Drakoen:
RAMSDIS 1 minute satellite imagery for the very latest.


Definitely wrapping up tighter now, lets see if it continues to consolidate......anyone able to analyze the upper level conditions? Are we favorable?
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Anyways back to Isaac...to me he's off the coast!
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I think the Republicans are gonna' have to cancel their convention. On the forecast track there'd be too much water in the area(5-7 feet), and there'd be a chance we could see groups milling about a convention center with no way to go anywhere. Sound familiar?
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Quoting flcanes:

again, i said this could get ugly if he gets off cuba before 18z


You very well may be right. I know the water is very hot, but I wonder how deep it is? If it's more shallow, he'd have to keep moving. Thoughts, anyone?
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For those of you wishing for a hurricane by you...watch this video and remember it.

http://www.youtube.com/watch?v=S68ksghDNg4

Member Since: August 4, 2011 Posts: 0 Comments: 288
1926. flcanes
Quoting uncwhurricane85:
boy we sure do have a lot of people on board the HH plane...taking readings from 22 north to on the coast of cuba...hahah....the MLC is off shore while LLC is right along the coast...convection is the MLC the spin in low levels is clearly right along the coast

it is not decoupled
Member Since: August 20, 2012 Posts: 13 Comments: 1247
The super rapid scan visible loops show that the center is inland. It will pop back out over water since it is just over a point that juts out. If it keeps its current heading, it will parallel the coastline for a while.
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1924. GetReal


The area of low pressure over the NW Carib currently has almost as much convection as Isaac.
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@Post 1852 I knew it wasn't long before a post like this went up...just wouldn't be the blog without one...
Member Since: August 14, 2010 Posts: 10 Comments: 16409
i here by now call 97L a fish storm


Member Since: May 21, 2006 Posts: 5091 Comments: 114719
So the new battle of models pits the...

GFS, CMC and Bamm Suite vs Euro, HWRF, GFDL and UKMET

who will win? TVCN seems to be closer to the Euro solution
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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.