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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111. VR46L
RIP Joyce...

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Quoting Bluestorm5:
It's way too early to be predicting a major in Gulf of Mexico. Haiti and Cuba is going to get hit by a tropical storm, if it didn't manages to reach hurricane strength, pretty good with the rain and winds. There will be mass flooding and mass deaths in both countries. After that, South Florida will get impacted and who know what's gonna happens after that? Wait and see, please...

This will be inland in 5 days...not exactly too early.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
NHC says Isaac hits the Gulf coast on Wed morning as an 80 mph storm. Doc Masters predicts a landfall at 'approaching cat 3'.

Think the Doc is probably nearer the mark.
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108. A4Guy
Quoting weatherman12345:
Ft lauderdale is out of the cone!


Just means the chance of the center moving over us is basically zero...but if the storm crosses thru the Keys or the southern tip of the peninsula, we will certainly feel TS-force gusts in Miami-Dade and Broward counties.
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Quoting weatherman12345:

You say the same thing every day.. it get really irritating


maybe to you can say I say it everyday
but I can tell you this last night boy was I ever so correct soo...
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NHC sticking with the TVCN on the western side of the guidance included in the map below.

Member Since: August 19, 2005 Posts: 5 Comments: 4863
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.

Thanks Doc.

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It's way too early to be predicting a major in Gulf of Mexico. Haiti and Cuba is going to get hit by a tropical storm, if it didn't manages to reach hurricane strength, pretty good with the rain and winds. There will be mass flooding and mass deaths in both countries. After that, South Florida will get impacted and who know what's gonna happens after that? Wait and see, please...
Member Since: August 1, 2011 Posts: 23 Comments: 7449
Quoting Maineweatherguy20023:

LOOK OUT!!


I'm ready! :)
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..everyone in florida..coast to coast..gets some of issac..remember the nws warning for the east coast of possible multiple tornado's..your on the east side of this storm..im sure they will strengthen the warnings in the coming days for all of us
Member Since: August 6, 2011 Posts: 4 Comments: 33232




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From Dr. Ryan Maue last night/early this morning before the 6z runs came out, for what it's worth.

Ryan N. Maue ‏@RyanMaue

HWRF 06z will be a model to watch as it will have the latest recon data & a better center location. That's rare to say.


NHC 06z tc-vitals has Isaac's center at 16.6°N 69.9° W ...that'll be garbage in for 06z GFS ...maybe relocate a smidgen ... center is ~15°N
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I normally am not very bold with anything once it interacts with so much land like Isaac will be doing - but SST's where Isaac is heading for waters that are approaching 90 degrees in the Gulf of Mexico. I think it could become a Category 2 hurricane, perhaps more if it slows down.
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A weak and disorganized core is better for Isaac because it won't take as long to recover as opposed to if it had a well defined one that took days to recover. As it stands, Cuba may weaken it by 10 mph.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
Multiple people shot outside NYC landmark

A gunman is shot dead by police after opening fire near the Empire State Building. Reportedly fired from job...

Link


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Looks like as of lately he has taken a more NW movement instead of WNW.

Land interaction with Hispanola may be keeping Isaac from wrapping around the convection and also pulling that slug of moisture over by Puerto Rico.

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Quoting alvarig1263:


I'm from Naples, FL on the SW coast.

LOOK OUT!!
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I am ready to know where this thing is going
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Quoting yoboi:
how many peeps from fla in here???


I'm from Naples, FL on the SW coast.
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12Z GFS Analysis running and a decent amount of RECCO Data on it:



Member Since: August 14, 2008 Posts: 4 Comments: 4881
Quoting 7544:
look at the cone maybe no watches at all for east side of fla except key west ?


Tropical Storm Force as of right now extend outward up to 185 miles. There will definitely be TS watches for South Florida later today since some of the winds will reach that area. Not sure about central or northern FL yet though.
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Quoting Articuno:
I predict a cat 2 riding the west coast of fl and cat 3 landfall near Cedar Key.

Ceder key no. N GOM yes agree with intensity
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Quoting TropicalAnalystwx13:
NHC was far too conservative with the intensity forecast.


A Cat 1 moving through the GOM when the water temps are in the upper 80s and lower 90s? Heck no!
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Quoting Elena85Vet:
Cat 3 is very realistic..


Climatology supports it. Recall how Katrina spun up quickly in the FL straits same time of the year.
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Quoting LargoFl:
OFF TOPIC BUT..multiple people have been shot outside the empire state building in NYC
just saw the newscast..1 dead 10 people injured
Member Since: August 6, 2011 Posts: 4 Comments: 33232
I can say with cinfidence that Mississippi Lousiana might be dodging this bullet. This is an eastward trend that was expected.
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Quoting 7544:
look at the cone maybe no watches at all for east side of fla except key west ?
Interests the remainder of Cuba...the remainder of the Bahamas... South Florida...and the Florida Keys should monitor the progress of Isaac. Watches will likely be required for portions of the Florida Keys later today and are also possible for portions of the southern Florida Peninsula.
Read more at http://www.wunderground.com/tropical/at201209.publ ic.html#heZ6lbcBcwkuPsTG.99
Member Since: August 28, 2006 Posts: 0 Comments: 591
Quoting LargoFl:
OFF TOPIC BUT..multiple people have been shot outside the empire state building in NYC


9, 2 dead including shooter. Shooter was put down by police.
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Quoting LargoFl:
OFF TOPIC BUT..multiple people have been shot outside the empire state building in NYC

SAD back to ISAAC now
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Quoting TropicalAnalystwx13:
NHC was far too conservative with the intensity forecast.


Good morning everyone! I'm not so sure they are wrong with the intensity forecast. Isaac is a very large storm with little vertical stacking. If it goes over land without being vertically stacked, it may take a significant amount of time for it to get its act together when it enters the GOM. In addition, there is the prospect of how close it comes to Florida.
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Quoting interstatelover7165:
What About the FLANALF? I think Issac is shooting for Charleston Sc.


I'm not familiar with the FLANALF.
I've noticed over the years that as a storm approaches the coast, the XTRP becomes much more reliable.
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you guys are focusing too much on the center of the line and not the cone itself..
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Quoting 7544:
look at the cone maybe no watches at all for east side of fla except key west ?


Look at the cone. T.S. Watches and Warnings for some of the Bahama Islands.
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I predict a cat 2 riding the west coast of fl and cat 3 landfall near Cedar Key.
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NOt me lol jk
Quoting yoboi:
how many peeps from fla in here???
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Quoting Elena85Vet:
Cat 3 is very realistic..

YES
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Southeast US Drought Monitor
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More time and near perfect conditions in the Gulf of Mexico? This situation is not turning out good, and we know what happens to storms at enter the Gulf in August with primed conditions. A Cat 3 landfalling at FSU, that should send the Met school there scrambling!
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Quoting sunlinepr:


Is this the real COC position?


YES
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Quoting LargoFl:
wait until the 5am tomorrow, this is just now unfolding with some new info, dont take your eyes off this one


One thing to remember... the cone is the envelope of average error for the center position. Miami & Ft Lauderdale will see some serious squally weather if the forecast track verifies. No... I don't live in Ft Lauderdale.
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Quoting 7544:
look at the cone maybe no watches at all for east side of fla except key west ?

Watches for Keys likely at 2
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Quoting Maineweatherguy20023:

i didn't see anything...
Interests the remainder of Cuba...the remainder of the Bahamas... South Florida...and the Florida Keys should monitor the progress of Isaac. Watches will likely be required for portions of the Florida Keys later today and are also possible for portions of the southern Florida Peninsula.
Read more at http://www.wunderground.com/tropical/at201209.publ ic.html#heZ6lbcBcwkuPsTG.99
Member Since: August 28, 2006 Posts: 0 Comments: 591
Cat 3 is very realistic..
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Is this the real COC position?

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OFF TOPIC BUT..multiple people have been shot outside the empire state building in NYC
Member Since: August 6, 2011 Posts: 4 Comments: 33232
how many peeps from fla in here???
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If Issac makes landfall along the current track it will be a blessing for the drought stricken regions of Georgia and Alabama


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by the way they shifted the cone West untill 72 hours then they pulled it East
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.