Isaac is strengthening

By: Dr. Jeff Masters , 2:58 PM GMT on August 24, 2012

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Tropical Storm Isaac is strengthening. An Air Force Reserve hurricane hunter aircraft measured surface winds of 60 mph on the east side of the center, about 170 miles south of Santo Domingo in the Dominican Republic, at 8:40 am EDT this morning. Winds at the aircraft's flight level of 5,000 feet were hurricane force, 76 mph. The surface pressure remained fairly high, at 1000 mb. Tropical cyclones have a warm core, and the Hurricane Hunters typically find that a storm's lowest pressure is also where the warmest temperature are. However, this morning's flight found that Isaac was still disorganized, with the storm showing almost no evidence of a warm core. Isaac's warmest temperatures were displaced 75 miles to the west of where the lowest pressure was. There were no signs of an eyewall beginning to build. Infrared and visible satellite loops show that Isaac is somewhat asymmetric, with a large band of intense thunderstorms to the east, separated from the core region. This is interfering with both the storm's low-level inflow and upper-level outflow, but the band appears to be dying out. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south.


Figure 1. Evening shot of Tropical Storm Isaac taken on August 23, 2012, by the NOAA Hurricane Hunters.

Isaac's rains
Radar imagery from Puerto Rico shows that Isaac is dumping some very heavy rains to the south and east of the center. Ponce, Puerto Rico had a wind gust of 37 mph this morning as a heavy band of rain moved through, and radar-estimated rainfall amounts are in excess of 7 inches for the region just north of Ponce. Power outages to 2,000 homes have been reported in Puerto Rico this morning. NOAA buoy 42085 offshore from Ponce reported a wind gust of 54 mph near 9 am EDT this morning. Rainfall estimates from microwave satellite instruments suggest that Isaac's heaviest rains are to the south of the center, and that the Dominican Republic and Eastern Haiti will escape the worst of Isaac's rains. Haiti's southwest peninsula and Eastern Cuba should suffer the heaviest rains.


Figure 2. Radar-estimated precipitation from the Puerto Rico radar shows the region near Ponce has received up to 7" of rain as of 10 am EDT August 24, 2012.

Latest model runs for Isaac
The latest set of 00Z and 06Z (8 pm and 2 am EDT) model runs have come into better agreement, thanks to the dropsonde mission by the NOAA jet yesterday afternoon and evening. Isaac should move over Haiti's southwest peninsula and then eastern Cuba, then track along the spine of Cuba before popping off into the Florida Straits on Sunday. A trough of low pressure will then pull Isaac to the northwest, and then north, towards the Central Gulf Coast. Landfall locations range from Mississippi (06Z HWRF model run) to the Florida Panhandle south of Tallahassee (06Z GFDL model run.) It is possible that the trough of low pressure pulling Isaac to the north may not be strong enough to pull Isaac all the way to the northeast and out to sea, and the ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.


Figure 3. Predicted 5-day rainfall total ending at 2 am EDT Wednesday August 29, from Tropical Storm Isaac. Graphics were generated from the 6Z (2 am EDT) August 24, 2012 run of the HWRF model. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.

Intensity forecast for Isaac
Isaac has not intensified as much as predicted, and I think that the storm's very large size is partially responsible for that. It's tough to spin up as much atmosphere as Isaac is attempting to do very quickly. Conditions remain favorable for intensification today, with wind shear low, 5 - 10 knots, ocean temperatures warm, 29°C, and dry air mostly mixed out of the storm's core. The large band of intense thunderstorms to the east, separated from the core region, appears to be dying out now, which will help the storm grow more organized. The storm's structure has improved considerably between 9 am - 10 am EDT, with a fairly tight center forming, exposed to view, on the north edge of Isaac's heaviest thunderstorms. A curved band of heavy thunderstorms is now trying to wrap around this center to the northeast, and this band will bring very heavy rains to Haiti and the Dominican Republic this afternoon. I expect that the Hurricane Hunters will observe a partial eyewall in their vortex reports between 2 - 4 pm EDT this afternoon. The storm's large size and disorganized structure suggests that Isaac will be able to intensify only slowly today, and will have top winds of 70 - 75 mph before encountering Southwest Haiti and Eastern Cuba tonight and Saturday. Isaac will likely be a 50 - 60 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate. The upper-level wind pattern favorable may be quite favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm--though the models disagree on whether or not this anticyclone will set up directly over Isaac or not. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 17% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. Tampa is in the NHC cone of uncertainty, though near the edge of it. At a minimum, Tampa will receive very heavy rains and wind gusts in excess of 40 mph. Isaac is going to be hard-pressed to bring hurricane-force winds to the city, though, since any path that takes it close to Tampa would keep the storm too close to land for significant intensification to occur. I put the odds of a mass evacuation being ordered for Tampa during the convention at 1%. I have detailed information on Tampa's storm surge vulnerability in a post from last week.

Invest 97L off the coast of Africa
A tropical wave that moved off the coast of Africa on Thursday has been designated Invest 97L by NHC this morning. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear of 10 - 20 knots. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Sunday morning. The 8 am EDT SHIPS model forecast predicts that 97L will track west-northwest over the next few days, and encounter a region of high wind shear associated with an upper-level low on Monday and Tuesday. This low may be capable of tearing the storm apart, as happened to Tropical Storm Joyce. None of the models currently foresee that 97L will affect the Lesser Antilles Islands, but 97L may pass near Bermuda 7 - 8 days from now.



20th anniversary of Hurricane Andrew
Today, August 24, is the 20th anniversary of Hurricane Andrew, which hit South Florida as a Category 5 hurricane with 175 mph winds--one of only three Category 5 hurricanes ever to hit the U.S. With Isaac churning through the Caribbean this week, I didn't have time to prepare a special post on Andrew, but our Hurricane Andrew archive page has links to satellite and radar images, newspaper headlines, and 49 YouTube videos. Here's an additional link for an Andrew damage video shot by wunderblogger/storm chaser Mike Theiss, when he was 14 years old.

Jeff Masters

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Looks like the mountains of Hispaniola are already affecting Isaac... and there is dry air into it...

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1010. Tygor
Quoting GBguy88:


I'm not Levi, but Cantore won't be there long. He'll jump around just as much as the models do.


If you don't want a storm to go to a certain place, have Cantore go there. This means virtually a 0% chance of a Mobile hit.
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Quoting BeanTech:
I was wondering when the NHC bashing would begin:

"What is the NHC thinking?"
"I don't buy it....the NHC is on crack!"
"How do those boneheads at the NHC not see this? It's plain as day!"

All coming from part-time, arm chair bloggers.

Happens every year....

Classic!
Yeah, it's easy to sit behind an anonymous handle and take potshots at the NHC folks. After all, people taking those shots are only doing so while in their cozy bedrooms listening to Justin Bieber and enjoying milk and cookies their mommies bring them; they're not doing the job of protecting millions of people and trillions of dollars of infrastructure under the glare of the national and global spotlight.

The people at the NHC are just that--people--so they're not above making mistakes (see: Debby). To err is human, and all that. But recognizing their humanity is one thing; insulting their intelligence, education, experience, and professionalism is something else altogether.
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Quoting StormTracker2K:


This is set up for the NHC to look really bad. It's almost like they are destin to make sure FL is caught off guard. Heck the mets in orlando are saying orlando has nothing to worry about now. Very strange watching the news here in Orlando as they fully believe the NHC is right on the money and we can expect little effects.



Cant be specific, but one of Orlando's station's in-house models showing landfall at Miami with exit at Tampa. I believe they have to stick with NHC forecasts.
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The wind forecast by the models might be low. This storm will track over very warm waters and with low shear and vertically stacked this could be a major storm. This is almost like the track Donna took maybe a little to the east.
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1006. wpb
good recon data very soon
Member Since: May 28, 2011 Posts: 0 Comments: 572
Time: 18:02:00Z
Coordinates: 17.6N 69.3667W
Acft. Static Air Press: 766.0 mb (~ 22.62 inHg)
Acft. Geopotential Hgt: 2,367 meters (~ 7,766 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 144° at 42 knots (From the SE at ~ 48.3 mph)
Air Temp: 11.1°C* (~ 52.0°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 44 knots (~ 50.6 mph)
SFMR Peak (10s) Sfc. Wind: 43 knots (~ 49.4 mph)
SFMR Rain Rate: 5 mm/hr (~ 0.20 in/hr)
(*) Denotes suspect data
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting GTcooliebai:
I agree with those coordinates and movement.


so does the NHC :) lol
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Quoting CarolinaHurricanes87:
Does anyone think this still has the potential for a Charley-like path? Cross over central Florida and then make its way up the SE coast? It seems as if the models can't decide whether they want to slow this system down near the gulf coast or curve it hard back to the NE.
no looks more and more likely like a hurricane irene path with a slight bend to the west
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Quoting StormTracker2K:
12Z Euro has now shifted east as well.

Lets wait and see in the next frame, before we jump the gun.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Does anyone think this still has the potential for a Charley-like path? Cross over central Florida and then make its way up the SE coast? It seems as if the models can't decide whether they want to slow this system down near the gulf coast or curve it hard back to the NE.
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One thing to gather from all this is that the cone needs to go back to cover the peninsula. Local METS were making it a point to highlight that most of PBC was out of the error cone now.
Member Since: August 19, 2005 Posts: 5 Comments: 5043
Quoting sunlinepr:

Going down again...




Sunline. Just want to say you post the best graphics, radars, etc. Thanks. :)
Member Since: August 24, 2010 Posts: 0 Comments: 680
Quoting StormTracker2K:
978mb and very near Tampa.



If it stays so close to land it will die, not strengthen.
The models dont understand that
Even the GFS strenghtens this practically on shore
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Quoting StormTracker2K:
12Z Euro has now shifted east as well.


That's the 0z.
Member Since: February 6, 2010 Posts: 0 Comments: 214
Quoting StormTracker2K:
12Z Euro has now shifted east as well.


You don't know that...
That's the same position it was at 00z... You have to Wait longer, to know that...
Member Since: October 3, 2010 Posts: 40 Comments: 4129
models now have a stronger system approaching South Florida so looks like if this trend continues hurricane watches may be needed for southern florida
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Quoting StormJunkie:


A better question would be which storm was it?
Andrew
Member Since: August 18, 2011 Posts: 0 Comments: 994
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The map...

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Quoting interstatelover7165:
How did you come up with that?


He was in the northern eyewall of Hurricane Andrew, as was I.
Member Since: August 13, 2007 Posts: 10 Comments: 4141
Quoting Levi32:
12z GFS ensembles suck Isaac NNW into Hispaniola and then bypass a lot of central Cuba. Still mostly west of Florida but a lot more members farther east than there were yesterday.



Looks like an @least 315 traj into the "shredder" (?)

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Quoting Seflhurricane:
if the NW motion continues Isaac will emerge just west of grand inagua in the bahamas and come much closer to Southern florida, this is not good at all and the TCHP over the florida traits is high


Okay, I've lurked over here all week. THIS comment scares the crap outta me and now I have a sinking feeling. My house was destroyed in Andrew (happy anniversary?) and my current home lost a roof in Wilma.

Going to get canned foods and fill up my gas tank. Got cash already, thank God.

Wow.
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Quoting HurricaneDean07:

Very Strong Hurricane...
Definition please? LOL

You say that.... Its a 982 MB storms which = weak Category 2... Not to say thats Weak... But...
When people say VERY STRONG HURRICANE, it typically means Cat 3+

Also... I thought I ignored you...
Grr. I hate these Ignore buttons... They never work.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting HurricaneDean07:

Very Strong Hurricane...
Definition please? LOL

You say that.... Its a 982 MB storms which = weak Category 2... Not to say thats Weak... But...
When people say VERY STRONG HURRICANE, it typically means Cat 3+


Cat 2 not strong. Have you ever experience 100mph winds? if not then keep quite. I have and it's not fun. I will never forget the noise of Charley as he was moving by eeast orlando.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting interstatelover7165:
How did you come up with that?


A better question would be which storm was it?
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Quoting interstatelover7165:
How did you come up with that?


Look at this image and see where is lists SW 184 St.
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Going down again?...


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Quoting hurricanehanna:


Thanks Will - edited and fixed :)



good girl and yvw
Member Since: September 19, 2005 Posts: 2 Comments: 4111
He is a BIG BOY!!

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The Florida Keys have always been in play for several days now but this current NW movement illustrates how much a difference of a few hundred miles, or a jog, can make. My Bud in Fort Lauderdale was texting me this am that the storm was going to miss him and they are back in play now (on the dirty side) for the time being.

You can never assume anything with this type of trajectory and uncertainty (Central Gulf/East Gulf/Florida/Bahamas-East Coast) until it emerges off the Northern Cuban coast.
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Quoting yoboi:


levi what's your thoughts with cantore in mobile????


I'm not Levi, but Cantore won't be there long. He'll jump around just as much as the models do.
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12Z Euro has now shifted east as well.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting kinsingmonster:
This storm will fall on the far eastern side of the cone. I predict that it will leave the very eastern side of Cuba. This leave over 300 miles until South Florida. I think landfall will be about 20 miles west of Miami as a cat 2.


I second that!
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HH descending now...
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Quoting will40:



to many htt in the addy hanna


Thanks Will - edited and fixed :)
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Quoting Stormchaser121:
I still believe in the more western path. The high that is over TX is moving to the northeast at this time, and the further east it goes, the more west the path goes. A lot of people are overlooking that. I do believe that as time goes by the path will shift more to the west again. Thats my idea from what im hearing from Local stations. TWC has anywhere from FL to Houston still in the watch area.
You are fooling yourself.
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972. yoboi
Quoting Levi32:


Thank you. I'm glad you like my site.


levi what's your thoughts with cantore in mobile????
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Quoting nrtiwlnvragn:


Northern Eyewall Never Again
How did you come up with that?
Member Since: August 18, 2011 Posts: 0 Comments: 994
Quoting StormTracker2K:
Very strong hurricane on the GFDL and right over Miami.


Very Strong Hurricane...
Definition please? LOL

You say that.... Its a 982 MB storms which = weak Category 2... Not to say thats Weak... But...
When people say VERY STRONG HURRICANE, it typically means Cat 3+
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting SFLWeatherman:
It GFDL is now on S FL


Yeah, but look at the finger of the ridge ahead of it. It should take a western jog on the next frame or two...
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967. FOREX
Quoting shawn26:
Can someone post the European model please?


not available yet.
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I, no matter where it goes, will be taping(VHS)coverage of Issac for as long as it lasts.
Member Since: August 18, 2011 Posts: 0 Comments: 994
Quoting zoomiami:


Spell out what your user name stands for? Probably a lot of people on here who don't know. Please


Northern Eyewall Never Again
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I still believe in the more western path. The high that is over TX is moving to the northeast at this time, and the further east it goes, the more west the path goes. A lot of people are overlooking that. I do believe that as time goes by the path will shift more to the west again. Thats my idea from what im hearing from Local stations. TWC has anywhere from FL to Houston still in the watch area.
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978mb and very near Tampa.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting StormTracker2K:
Very strong hurricane on the GFDL and right over Miami.

That is the strongest the GFDL has shown yet. HWRF already on board for a Hurricane and they are like brother and sister model I believe.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Looking at the factors in play on the Euro it looks like it will kick into the gulf rather substantially away from the FL W coast then turn N or NNE into the panhandle. We'll see....
Member Since: February 6, 2010 Posts: 0 Comments: 214

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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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