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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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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1920. flcanes
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.

it should draw isaac to it
Member Since: August 20, 2012 Posts: 13 Comments: 1247
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
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Quoting lobdelse81:

What? I see no foul language in the previous statement, relax:)

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!
Member Since: June 4, 2012 Posts: 0 Comments: 767
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.
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Quoting flcanes:

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


It's off cuba from what I can see.
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1915. GetReal
Isaac is hugging the northern Cuban coast near Bahia Rio Seco region. Satelitte and the wind direction changes recon has found seem to confirm that.

Link
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1914. flcanes
Quoting PalmBeachWeather:
Are you my bf? Is this your handle?

hmmm?!?
Member Since: August 20, 2012 Posts: 13 Comments: 1247
Quoting Drakoen:
RAMSDIS 1 minute satellite imagery for the very latest.


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.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1912. flcanes
Quoting caneswatch:


Kait is the best LOL

dr. rick knabb
Member Since: August 20, 2012 Posts: 13 Comments: 1247
Quoting caneswatch:


Kait is the best LOL
Are you my bf? Is this your handle?
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Today's Video Blog Update!!
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Not even mother nature knows where that storm is going....so how can we? The models do a great job but how much do you put in your local forecast for next Tuesday....LOL.
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1908. flcanes
Quoting PalmBeachWeather:
Very nice in St. Louis

it should be depending on how far east isaac goes
Member Since: August 20, 2012 Posts: 13 Comments: 1247
Quoting PalmBeachWeather:
But my bf thinks Kait is the best.LOL


Kait is the best LOL
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1906. flcanes
Quoting muddertracker:


Looks like the llc is back in the water...now things get interesting.

again, i said this could get ugly if he gets off cuba before 18z
Member Since: August 20, 2012 Posts: 13 Comments: 1247
Quoting DookiePBC:
Dang...just got a call from American Airlines that my flight from St. Louis to Ft Lauderdale for tomorrow afternoon is canceled. Hoping to get an earlier flight either tonight or first thing tomorrow. How bad is it supposed to be!?
Very nice in St. Louis
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1904. 900MB
This thing is at 21N, under the blob of new convection. Further off the coast than many think!
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Quoting STXHurricanes2012:

Language please!!! Follow the rules!

What? I see no foul language in the previous statement, relax:)
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1902. Drakoen
Quoting cchsweatherman:


Where do you get 6 HR positions for the ECMWF from? All the sites that I know with ECMWF output only have 24 hour increments.


On the Wunderground model page.
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Quoting RTSplayer:


At this point yes, Georges and Rita are probably the two best analogs.

The models keep flip-flopping but the general idea is that depending on the timing and how the ridges and troughs move, it just might jump farther west.

Because the Euro flip-flopped so hard this time, I don't trust any model until another 12 hours so we can see if the fix themselves.


Best be for now, IMO, is assume Mobile Bay gets an eye-wall and plan for that depending on where you live...


Well, that would be where I live...lol!
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1900. Drakoen
RAMSDIS 1 minute satellite imagery for the very latest.
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The spread in the models is greater than ever - I just looked at 12Z HWRF - that has shifted from panama city area to almost cedar key area and the 12Z GFDL has shifted from NO to Destin. It doesn't look like a trend for more than 12 hours can be established with this storm! Frustrated with preparations!
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Quoting E46Pilot:


Agreed....I miss Don Knoe though. I like Steve Weagle
Weragle is very good for a local guy... Glaser spends too much time trying to be an actor..
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Quoting StormHype:
One thing for sure is it looks like cr*p at the moment.


Patience, this thing just ran through Haiti and Cuba and is still alive. That in itself is a rare feet for tropical storms to do.
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Quoting Drakoen:
Current position matches up best with the 12z EURO 6hr position out of all the 12z models which had Issac going over Banes, Cuba.


Where do you get 6 HR positions for the ECMWF from? All the sites that I know with ECMWF output only have 24 hour increments.
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Dang...just got a call from American Airlines that my flight from St. Louis to Ft Lauderdale for tomorrow afternoon is canceled. Hoping to get an earlier flight either tonight or first thing tomorrow. How bad is it supposed to be!?
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At 2 p.m. (3.00 EST) the Cayman Islands National Weather Service and the National Hazard Management Executive Committee lifted the Tropical Storm Watch for the Cayman Islands.
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1892. Michfan
Quoting flcanes:

nope


With land interaction yes.
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Quoting wpb:
max is vgood the others are bozos


Agreed....I miss Don Knoe though. I like Steve Weagle
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Quoting muddertracker:


Looks like the llc is back in the water...now things get interesting.


Yep.
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Ever been up that high?  bad weather can be a nightmare.  Anyway get used to that kind of reporting showing up here.
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

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Quoting tennisgirl08:


Analog storm for Isaac? Hurricane Georges. Bryan Norcross just mentioned this analog on TWC.


At this point yes, Georges and Rita are probably the two best analogs.

The models keep flip-flopping but the general idea is that depending on the timing and how the ridges and troughs move, it just might jump farther west.

Because the Euro flip-flopped so hard this time, I don't trust any model until another 12 hours so we can see if the fix themselves.


Best be for now, IMO, is assume Mobile Bay gets an eye-wall and plan for that depending on where you live...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting flcanes:

now who's calling mr. knabb bozo
I like Mr. Knabb... Finally someone that can speak
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1886. airmet3
Quoting GTcooliebai:
Experimental FIM-8 66 hrs. shows a wide swath of TS force winds effecting the West Coast of FL.


Why are you posting this particular model? Is there something about this model that leads you to believe it is the most correct?

I'm not flaming, I'm just asking.
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1885. flcanes
Quoting TomballTXPride:

Was to be expected.

nope
Member Since: August 20, 2012 Posts: 13 Comments: 1247
Quoting Civicane49:
Hey guys. I'm back.

I'll probably come to this site almost everyday to see what's new.

I see that Isaac is currently affecting the northern Caribbean Islands, and is expected to become a hurricane and threaten the southeastern United States.



Looks like the llc is back in the water...now things get interesting.
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1883. flcanes
Quoting TomballTXPride:


Yep. Exactly. A very large system, a shallow continental shelf, and a possible perpendicular landfall moving at that speed toward the coast.

With those elements alone, I wouldn't be surprised one bit if this equaled or perhaps surpasses IKE's surge if he manages to pull together category 3 strength--which he very well might do.

oh no
Member Since: August 20, 2012 Posts: 13 Comments: 1247
1881. Michfan
Recon turning around for another pass.
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Responding to Isaac Link
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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


I can't agree more. I actually rather look at ways in which it would fizzle, so I am more of a fizzlecaster. I also lost everything in Katrina. By the way Next wednesday is the 7th aniversary of Hurricane Katrina affecting the Gulf Coast.
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One thing for sure is it looks like cr*p at the moment.
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1877. flcanes
Quoting wpb:
max is vgood the others are bozos

now who's calling mr. knabb bozo
Member Since: August 20, 2012 Posts: 13 Comments: 1247
1875. Michfan
Product: Air Force Temp Drop (Dropsonde) Message (UZNT13 KNHC)
Transmitted: 25th day of the month at 19:33Z
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: 05

Part A...

Date: Near the closest hour of 19Z on the 25th day of the month
Highest Mandatory Level For Which Wind Was Reported: 850mb
Coordinates: 21.5N 75.9W
Location: 102 miles (164 km) to the N (357°) from Santiago de Cuba, Cuba.
Marsden Square: 080 (About)

Level Geo. Height Air Temp. Dew Point Wind Direction Wind Speed
1001mb (29.56 inHg) Sea Level (Surface) 26.4°C (79.5°F) 24.5°C (76.1°F) 75° (from the ENE) 39 knots (45 mph)
1000mb 6m (20 ft) 26.4°C (79.5°F) 24.5°C (76.1°F) 75° (from the ENE) 38 knots (44 mph)
925mb 691m (2,267 ft) 21.2°C (70.2°F) 21.1°C (70.0°F) 85° (from the E) 45 knots (52 mph)
850mb 1,423m (4,669 ft) 17.8°C (64.0°F) 17.6°C (63.7°F) 95° (from the E) 41 knots (47 mph)

Information About Radiosonde:
- Launch Time: 19:21Z
- About Sonde: A descending radiosonde tracked automatically by satellite navigation with no solar or infrared correction.

Remarks Section...

Splash Location: 21.46N 75.9W
Splash Time: 19:23Z

Release Location: 21.46N 75.87W
Release Time: 19:21:14Z

Mean Boundary Level Wind (mean wind in the lowest 500 geopotential meters of the sounding):
- Wind Direction: 80° (from the E)
- Wind Speed: 42 knots (48 mph)

Deep Layer Mean Wind (average wind over the depth of the sounding):
- Wind Direction: 85° (from the E)
- Wind Speed: 43 knots (49 mph)
- Depth of Sounding: From 843mb to 1000mb

Average Wind Over Lowest Available 150 geopotential meters (gpm) of the sounding:
- Lowest 150m: 159 gpm - 9 gpm (522 geo. feet - 30 geo. feet)
- Wind Direction: 75° (from the ENE)
- Wind Speed: 40 knots (46 mph)

Sounding Software Version: AEV 20802

Part B: Data For Significant Levels...

Significant Temperature And Relative Humidity Levels...
Level Air Temperature Dew Point
1001mb (Surface) 26.4°C (79.5°F) 24.5°C (76.1°F)
850mb 17.8°C (64.0°F) 17.6°C (63.7°F)
843mb 17.0°C (62.6°F) 17.0°C (62.6°F)

Significant Wind Levels...
Level Wind Direction Wind Speed
1001mb (Surface) 75° (from the ENE) 39 knots (45 mph)
983mb 75° (from the ENE) 44 knots (51 mph)
962mb 85° (from the E) 40 knots (46 mph)
955mb 85° (from the E) 43 knots (49 mph)
936mb 85° (from the E) 43 knots (49 mph)
900mb 90° (from the E) 49 knots (56 mph)
855mb 95° (from the E) 42 knots (48 mph)
843mb 95° (from the E) 39 knots (45 mph)

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Quoting 954FtLCane:


Max Mayfield the former national hurricane center coordinator mentioned this. Thats who they are. It's not your little channel 5 wpb rinky dink weather.......
But my bf thinks Kait is the best.LOL
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I still think its offshore but I guess we'll see
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WPLG Miami (Channel 10) live feed: Link
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Hey guys. I'm back.

I'll probably come to this site almost everyday to see what's new.

I see that Isaac is currently affecting the northern Caribbean Islands, and is expected to become a hurricane and threaten the southeastern United States.

Member Since: Posts: Comments:

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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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