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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1821. flcanes
Quoting LargoFl:

looks like a cat3 pushing a devastating surge into tampa, which will only pile up, causing the equivalent of a cat5 surge
were talking 20-30 feet of water
Member Since: August 20, 2012 Posts: 13 Comments: 1254
The center is showing itself here:

Link

This corresponds well with the 999.1 mb reading

The center is just off shore from Bahia Rio Seco
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Link Floater
If you click on forecast points, it looks to be going pretty much as plotted.
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1818. Levi32
Quoting RTSplayer:
Significant re-intensification occurring in the NE quadrant as per radar, which refreshes much faster than most public satellite products.



GOES-14 super rapid scan (1-minute intervals) refreshes faster than the radar.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
I just got back in from doing some yard work, what is everyones thoughts on the ECMWF 12Z? That track is a disaster for me in Tallahassee. Any insight would be appreciated and what are the thoughts on that model shifting back east? Will it start another trend?
Member Since: September 5, 2008 Posts: 0 Comments: 63
1816. GetReal
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Quoting naplesdoppler:
Long time lurker here, where is Orca with his tracks and maps??


Havent seen him since the buyout.
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Analog storm for Isaac? Hurricane Georges. Bryan Norcross just mentioned this analog on TWC.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
.
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1812. MahFL
Quoting Maineweatherguy20023:

Center is over land right now i beleive and i guess they cant go over Cuba


HH don't fly over land anyways, they can though fly in Cuban airspace when the Cuban gov ok's it, which they normally do when a Tropical Cyclone is a threat.
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1811. Drakoen
Looks like the center is just off shore based on the recon data and satellite imagery, northeast of Banes, Cuba.
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1810. wpb
Quoting 954FtLCane:
Channel 10 Miami confirms center of circulation is just off the north coast of Cuba.
who are they
Member Since: May 28, 2011 Posts: 0 Comments: 573
Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressures are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.




Center reforming maybe closer to convection?
Member Since: May 17, 2006 Posts: 6 Comments: 1367
Quoting stormwatcherCI:
Of course they are. Information received from the HH is shared with the Cuban Govt and they have always allowed them to fly in their air space.

Clearly not over there land
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Long time lurker here, where is Orca with his tracks and maps??
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1806. angiest
Quoting robj144:


Like I said, no one's perfect, but how often does something like this happen within the last 10 years? Maybe 5% of the time...


Which is why Debby sticks out like a sore thumb.
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1804. GetReal
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Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressures are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.

It is possible the plane is missing the center a good deal to the north at the moment, which could explain it.



Going by radar imagery and the 2PM center estimate they are only between 30 and 45 miles N of the supposed center where those pressures are being reported.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting TropicalAnalystwx13:
Off-topic, but..

According to NBC News, the first man ever to set foot on the moon, has died at the age of 82.


One of my childhood heroes. I remember catching a bus to downtown Houston for the ticker-tape parade.
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Channel 10 Miami confirms center of circulation is just off the north coast of Cuba.
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I'm gonna assume at least half the GFS members have it getting on the back side of that ridge, totally crossing the bridging between the two ridges...


Link

That one track is so similar to Ike and Rita, it's like the same thing...just a tiny change in timing now and the whole forecast could be blown...by hundreds of miles even...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressures are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.

It is possible the plane is missing the center a good deal to the north at the moment, which could explain it.



The center is inland or barely off the coast. It's fairly obvious on satellite.
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Quoting CaneHunter031472:
Are my eyes playing tricks on me? Can someone please correct me if I'm wrong? Is this now making landfall between MS and AL according to the GFS? or is this an early model cycle?



Tracks change often and this is several days out. Until there is a consensus over several runs, I would not worry.
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Quoting TropicalAnalystwx13:

It has made sense all along.


Euro went back east, so it isn't cutting the corner on the ridge.
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Quoting HurricaneDean07:

They passed by the center... I don't know what they're doing.

Isn't it obvious they are sampling the environment around Isaac??
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1795. flcanes
Quoting JBirdFireMedic:



Agreed!

uggh, expect with these model runs for mass evacuations from panama city to galveston at this rate
Member Since: August 20, 2012 Posts: 13 Comments: 1254
Short Wave Loop

To the eye it appears the coc is scooting along the northeastern Cuba coast.
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1793. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 38521
1792. GetReal
Quoting Michfan:


Yeah i recall there being a custom product by them where you can input how many frames you wanted width height etc. Just can't seem to find it anymore.
\


Here is the site I think that you wanted....

Link
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Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressures are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.

It is possible the plane is missing the center a good deal to the north at the moment, which could explain it.


Center is over land right now i beleive and i guess they cant go over Cuba
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Quoting Maineweatherguy20023:

Theve been in Cuban Airspace for 20 min now...
Raul is more tolerant, don't worry guys, things are changing in Cuba...
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Quoting louisianaboy444:


I did not cry when the models shifted east...you were jumping the gun on the models shiftting east before they even came out...you have been the one that has been wishcasting it to the panhandle this entire time....I live in Western LA so I am out of it as it is..you are the one that has the bias and it is quite obvious...I'm just stating what the GFS is showing, a model that all of a sudden has no bearing with some of the Florida folks...you really need to stop


lmao, um no, they 00Z models DID shift east last night and someone jumped on before they were out and said the track would be shifted west due to the fact that the 00Z models shifted west, when in fact they had not come out

you apparently did not read the blog very well last night

Also about the GFS, um if someone feels a system is going to go to a certain place, of course they are going to disagree with a run that does something totally different, its called sticking with your forecasted thinking
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Quoting RTSplayer:
Center consensus is Mobile Bay, which is almost exactly what I expected all along...

...but wow, look how many west-leaning ensemble members there are now...this is a nightmare for forecasting.




Hopefully in 12 hours when 2 more GFS runs and another Euro run are done, this crap will get sorted out better.


This cycle is a disappointment, because it added more uncertainty rather than decreasing it...

At least the intensity forecast is starting to agree somewhat, but that's a shame too, because they are all pretty strong now.



That's what MSX was trying to show earlier. Euro cannot be taken as written in stone with GFS looking like this.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
Quoting CaneHunter031472:
Are my eyes playing tricks on me? Can someone please correct me if I'm wrong? Is this now making landfall between MS and AL according to the GFS? or is this an early model cycle?


Not your eyes.
Member Since: July 6, 2010 Posts: 113 Comments: 32069
1786. flcanes
Quoting CaneHunter031472:
Are my eyes playing tricks on me? Can someone please correct me if I'm wrong? Is this now making landfall between MS and AL according to the GFS? or is this an early model cycle?


pretty close, maybe mobile bay though
Member Since: August 20, 2012 Posts: 13 Comments: 1254
Quoting RTSplayer:
....Hopefully in 12 hours when 2 more GFS runs and another Euro run are done, this crap will get sorted out better.


This cycle is a disappointment, because it added more uncertainty rather than decreasing it...

At least the intensity forecast is starting to agree somewhat, but that's a shame too, because they are all pretty strong now.




Agreed!
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Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressure are rising closer to the center, with the pressure minimum found so far off to the east by a good ways.


They passed by the center... I don't know what they're doing.
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Quoting violet312s:
Looks like recon not allowed to enter Cuban airspace. :(
Of course they are. Information received from the HH is shared with the Cuban Govt and they have always allowed them to fly in their air space.
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Levi
What's your take on this??
Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressure are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.

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yep!
Quoting CaneHunter031472:
Are my eyes playing tricks on me? Can someone please correct me if I'm wrong? Is this now making landfall between MS and AL according to the GFS? or is this an early model cycle?


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Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressure are rising closer to the center, with the pressure minimum found so far off to the east by a good ways.




Which means SIR
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1779. flcanes
Quoting Levi32:
This is a little odd. Recon is flying at a constant altitude but extrapolated pressure are rising closer to the center, with the pressure minimum found so far off to the east by a good ways.


maybe centre relocation
Member Since: August 20, 2012 Posts: 13 Comments: 1254
Are my eyes playing tricks on me? Can someone please correct me if I'm wrong? Is this now making landfall between MS and AL according to the GFS? or is this an early model cycle?

Member Since: August 1, 2007 Posts: 0 Comments: 179
1777. robj144
Quoting angiest:


Debby's first 3 or 4 forecasts may well be the absolute worst the NHC has put out in a decade (in terms of where the storm ultimately went, they were actually reasonable). I personally don't remember seeing such a dramatic shift in a forecast as that.


Like I said, no one's perfect, but how often does something like this happen within the last 10 years? Maybe 5% of the time...
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1776. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 38521
Quoting Hurricanes101:


just like you whined when the tracks shifted east last night?

fact is the models are in less agreement now then they were yesterday, lets see how this progresses, but a stronger Isaac will be further east


I did not cry when the models shifted east...you were jumping the gun on the models shiftting east before they even came out...you have been the one that has been wishcasting it to the panhandle this entire time....I live in Western LA so I am out of it as it is..you are the one that has the bias and it is quite obvious...I'm just stating what the GFS is showing, a model that all of a sudden has no bearing with some of the Florida folks...you really need to stop
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Recon flew north of the center.... Found 999.4 Pressure.
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1773. flcanes
Quoting Grothar:

pretty good consensus there
Member Since: August 20, 2012 Posts: 13 Comments: 1254
1772. Levi32
This is a little odd. Recon is flying at a constant altitude but extrapolated pressures are rising closer to the center, with the pressure minimum found so far (999mb) off to the east by a good ways.

It is possible the plane is missing the center a good deal to the north at the moment, which could explain it.

Member Since: November 24, 2005 Posts: 635 Comments: 26647
There looks like there was a glitch in the UKMET model:

42 hrs.



48 hrs.

Member Since: August 31, 2009 Posts: 0 Comments: 5628

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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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