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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Monroe County Schools
Tropical Storm Information:

Due to the predicted weather conditions associated with Tropical Storm Isaac all Monroe County Schools, offices and facilities will be closed on Monday, August 27th. Identified shelter locations at: Key West High School, Switlik School and Coral Shores High School will open in accordance with directives from Monroe County Emergency Management. Note, Sugarloaf School has not been identified as a shelter location for this event.

Monroe County Emergency Management:

Tropical Storm Isaac, according to the National Hurricane Center’s 8 a.m. advisory now has sustained winds near the center at 50 mph. It is moving to the west at about 15 mph. According to the NHC latest track, the center of the storm should be over or near the Lower Keys late Sunday evening as a strong tropical storm.

Tropical storm-force winds are likely to begin affecting the Upper Keys Sunday morning, according to Chip Kasper, a forecaster at the Key West National Weather Service office.

A decision regarding visitor evacuations for the Keys is expected to be made later today, according to Irene Toner, director of Monroe County Emergency Management.

A full advisory is to be issued after that decision is made.


Shelters will be opened at 2:00 PM Saturday.
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According the Dr. Masters recent blog, Tampa only has a 1% chance of getting hurricane winds from Isaac.
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Quoting MississippiWx:
Final landfall is almost exactly the same on the 12z GFS. It just makes a little more interaction with the peninsula/S Florida than 6z.


And that is what will make such a huge difference on potential impacts to South FL, and will affect how strong a hit the panhandle gets.
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Quoting tkdaime:
I live in s florida I see people are starting yo put up there shutters I just moved here guess I don't know what I'm in for
guess we all can count on flooding rains, maybe tree's down..but we can surely count on loss of power, and blackouts...we lost power here the other day just from a good thunderstorm
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Quoting oracle28:
On a serious note, could the interaction with the islands, be pulling Isaac northward, due to frictional drag?


Absolutely and why it matters where it pops off the N coast.
Member Since: August 19, 2005 Posts: 5 Comments: 5174
355. ch2os
Quoting FrancesJeanne:


Port St. Lucie here


Ft Pierce
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Quoting SWLACajun:
Dirty side is NE quadrant correct?


correct - Morgan City here ;-)
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Quoting wunderkidcayman:
16.1N 70.7W if that area is the LLCOC it is moving or wobbled now W it looks like


This is getting too funny.
Member Since: September 2, 2006 Posts: 110 Comments: 6874
Let's see what the ECMWF shows for its 12z run? If it shifts east....UH OH!
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Quoting NICycloneChaser:


Yes. Still brings it back just over the gulf for a second landfall in the panhandle though.


Yes indeed, this is "Definitely" going into the Gulf. After a few other possible landfalls.
Member Since: August 19, 2005 Posts: 5 Comments: 5174
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This is from the NOAA Hurricane Hunters
NOAA42 radar image from inside Isaac. This is 10hrs ago.

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Whew!! Pensacola's out of the woods!

(Just kidding...)
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For now the bullseye is on Destin, Fl but due to uncertainty with track and intensity everyone from
Ms coast eastward to Bahamas should be alert.
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Quoting swflpaul:
No worries folks! The Uber-Rich down here in Naples will be activating their weather shield so issac (whatevr is left of him) will bounce rite off & up the coast! Someone was asleep at the controls when Wilma was approaching otherwise...


We're preparing here in Naples. Knew it would have some kind of impacts ever since the storm formed a few days ago. I don't know about others in NAples but I know I'm not letting my guard down. Already stocked up at Wal-Mart :)
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HH should be going out in 29 min.
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On a serious note, could the interaction with the islands, be pulling Isaac northward, due to frictional drag?
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Quoting FrancesJeanne:


Port St. Lucie here


Key West here!
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Quoting AussieStorm:
Tormenta tropical Isaac. Una foto de como esta inundada la panamericana a la altura de San Antonio




Tropical Storm Isaac is having an impact on two more cruise ships sailing out of Florida.

Royal Caribbean says the 2,350-passenger Majesty of the Seas and 2,390-passenger Monarch of the Seas will not call this weekend at CocoCay, the line's private island in the Bahamas. The ships are setting sail today from Florida's Port Canaveral and Port of Miami, respectively.

The announcement brings to five the number of vessels affected by Isaac. Industry giant Carnival's 2,974-passenger Carnival Valor skipped a call Thursday in Curacao to stay ahead of the storm. The ship instead is today visiting Nassau in the Bahamas. Another Carnival ship, the 2,978-passenger Carnival Liberty, also is visiting Nassau today after skipping a call Thursday in Grand Turk.

Also on an altered course this week due to Isaac is Royal Caribbean's 5,400-passenger Allure of the Seas, which departed from Fort Lauderdale on Sunday. The world's largest cruise ship has sailed for the Western Caribbean instead of heading to the Eastern Caribbean as planned. It's visiting Falmouth, Jamaica and Cozumel, Mexico instead of St. Thomas and St. Maarten.

As of 11 a.m. ET, Isaac was 165 miles south-southwest of Santo Domingo, Dominican Republic and moving to the west-northwest at 14 miles per hour. The storm has maximum sustained winds of 60 miles per hour.
geez..just look at all that water..this is whats coming to florida next week, no mountains but plenty of lakes and streams and ponds to overflow and flood everything
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I rather wait till recon gets there as NHC said it still has multiple LLC so it really could be anywhere

but I think they are between 15.5N and 16.5N
Member Since: June 13, 2009 Posts: 2 Comments: 11657
Colorado State's tracker has re-positioned itself to roughly a compromise between my fix and the NHC fix.




Not that it matters much, but I do point out this tool bounces around a lot and it tends to north cast stuff, so this correction may be overshooting back to the south, but it clearly does not like the NHC position either.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Final landfall is almost exactly the same on the 12z GFS. It just makes a little more interaction with the peninsula/S Florida than 6z.
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I live in s florida I see people are starting yo put up there shutters I just moved here guess I don't know what I'm in for
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Hey me two lol
Quoting trey33:
Wow ... maybe Levi was right?
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Quoting AussieStorm:
Tropical storm Isaac in Dominican Republic



An that it didn't went over DR. Certainly pulling a lot of moisture on its eastern side.
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Quoting E46Pilot:
I wonder if this model shift has anything to do with all of the data they were waiting on from the Gulf stream aircraft?


I am sure it has everything to do with that data E46
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333. 7544
you know the nhc is watchin this run they must be going nuts lol
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Quoting ProgressivePulse:
So the 12Z GFS is showing a SEFL landfall now?


Yes. Still brings it back just over the gulf for a second landfall in the panhandle though.
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I'm still not sold on a Panhandle landfall. I think he turns more toward the NNW after 63 hrs than the model indicates.
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Link
My forecast
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Wow ... maybe Levi was right?
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325. bwi
I know they'll probably wait for the next HH mission, but I think it's time to upgrade the tropical storm warnings to hurricane warnings for the DR and Haiti and Cuba, and upgrade the watches to hurricane watches.

Just looking at the massive size of Isaac, and all that warm water, there's a lot of potential energy out there. It could come together quicker than currently predicted in my opinion. It probably won't, but it could, and since intensity forecasts are so uncertain, I think I'd prefer to err on the side of extra warnings at this time. Just my opinion.
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So the 12Z GFS is showing a SEFL landfall now?
Member Since: August 19, 2005 Posts: 5 Comments: 5174
Tropical storm Isaac in Dominican Republic

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321. auburn (Mod)
Quoting presslord:
Now that she's a colleague Of Jeff Masters....I better be careful what I say about Stephanie...lest I rack up a penalty....


I dont think you can help yourself old man...LOL
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Quoting rattnroll:
Been watching for awhile and been on this blog many times and man you guys (except a select few) are on the ball and smart as hell!! I am a met in the Navy stationed at NAS JAX however I live near Starke, FL and I have been watching this and watching the models bounce all over as well.
welcome,glad your here with us
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Quoting WxLogic:


Correct... you don't want to be on the NE/E/SE periphery of a tropical system.


Thanks all!
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On the latest infrared, the center is gaining convection.

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Quoting cybergrump:
You can see where center is clear now on this image.Link


Really like this view. Thanks.
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Am I correct in assuming that the strongest largest wind field is to the N of Isaac?

Has anyone got links to wind field model illustrations?
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The long awaited and anticipated Reed Run is finally here...



Based off Steering Layers and pattern trends, I see Isaac moving a bit further east of the official NHC track and right in line with the model consensus. Look here at the steering layers for a strong TS, which Isaac is right now.



Developing ridge will not allow Isaac or any storm to bust through so east of 85W (as I stressed over the past few days) he will go. I see a recurvature when Isaac reaches Tampas latitude.

Steering Layers for a Hurricane - Category 1


A stronger storm will steer Isaac closer to the peninsula.

So those are my thoughts on the storm.
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Ridging is weaker at 84 hrs. Look for a drift toward the NNW toward Apalachicola.

As expected, NHC will likely have to shift east at 5 pm.
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"I think the GFS tried to pull a Henry Margusity there..."
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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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