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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1061. Dunkman
Quoting GetReal:


Euro 12z back to NOLA...


That is yesterday's run.
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Okay - there was a post on facebook that our fire district here in Gulf Breeze, FL is already giving away sand bags? Guess they see a heavy rain event on the way?
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Quoting GetReal:


Euro 12z back to NOLA...


oh now let's just stop this nonsense right now, k ? lol

I think I actually saw models in my sleep last night.
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1058. LargoFl
GFS at 72 hours
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Quoting Levi32:
Ooooh yeah, haven't seen these colors yet on my new maps:



Lots of 50 and a 55kts.

Hmm...63.25mph, so rounds up to 65mph...in terms of what would be reported. Though they will want more than one flag at that intensity to go with it.

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Quoting WDEmobmet:
Jim Cantore arrived at Gulfport MS


Well, then Gulfport is safe for now.
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Quoting zoomiami:


He was in the northern eyewall of Hurricane Andrew, as was I.


Wow. I know y'all don't EVER want to that again!
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Quoting GetReal:


Euro 12z back to NOLA...


GOOD GRIEF!! this is crazy. What does Isaac have up his sleeve?
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Jim Cantore arrived at Gulfport MS
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Here in Santo Domingo we are feeling Isaac's winds (tropical storm gusts) but no significant rain yet.
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Mid level wind shear.

Link
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Quoting GeorgiaStormz:


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


The way it looks now its not at all out of possibility that Isaac gets shredded by the mountains. Though he is getting better organized, he is still disorganized. The mountains could really put a hurt'n on his circulation, especially if decides go over both Haiti and Eastern Cuba.

We are going to have to wait to see how this thing plays out after it gets north of the Haiti/Cuba parallel. Even then it won't have much room to gather too much energy, so it should keep it no higher than a CAT 1 before Florida. The only way this thing becomes a beast is if it gets entire core away from land for a long duration and I don't see that happening.
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Quoting HoustonTxGal:


If he can get a flight out of Miami.
4 flights per day on JetBlue from Fort Lauderdale-Hollywood International
Member Since: October 5, 2007 Posts: 0 Comments: 64
Isaac appears to be taking in a lot of dry air at the moment, probably won't be intensifying anymore until it passes the islands if it does get to the north of them.
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17.500N 69.500W
SFMR
59 knots
(~ 67.8 mph)

That's pretty far from the center too.
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67 mph wind.

Time: 18:05:00Z
Coordinates: 17.5N 69.5W
Acft. Static Air Press: 842.9 mb (~ 24.89 inHg)
Acft. Geopotential Hgt: 1,547 meters (~ 5,075 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 150° at 45 knots (From the SSE at ~ 51.7 mph)
Air Temp: 12.7°C* (~ 54.9°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 49 knots (~ 56.3 mph)
SFMR Peak (10s) Sfc. Wind: 59 knots (~ 67.8 mph)
SFMR Rain Rate: 26 mm/hr (~ 1.02 in/hr)
(*) Denotes suspect data
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1043. wpb
Quoting LargoFl:
old
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1042. GetReal
<
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1041. LargoFl
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Quoting PublicAdjuster2:
Any chance this eventually hits New England?


If he can get a flight out of Miami.
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Quoting zoomiami:


If this works right the bolded coordinates place the storm not too far off miami at 25.7 80.4


Hi Zoo, long time since I've seen you here!

Wow, as I was starting to actually say yesterday, I think we here in SE Fla are in the clear....
now this thing may come back and bite us...

back to watching... at least we are "ready" at my house...
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1038. hulakai
climatology again serves up two interesting analogues.

Gustav 8/25/08-9/5/08 to NOLA cat 2 landfall and
Ernesto 8/24/06-9/4/06 TS up Fla. spine. Coincidentally pretty much within the NHC cone.

Right now, to me, Ernesto looks more likely which may give us some foul weather here in SFL., but better outcome.
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Quoting GTcooliebai:
This was from San Juan as Isaac passed South of Puerto Rico, he's a Big Boy!



likely the band this morning, but not the storm core.
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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 leaves over 300 miles until South Florida. I think landfall will be about 20 miles west of Miami as a cat 2.



lol that may be overding it a bit rofl
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saturated.land.in.florida.
Member Since: September 11, 2010 Posts: 1 Comments: 4350
Euro 72 hrs.

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1032. Levi32
Ooooh yeah, haven't seen these colors yet on my new maps:

Member Since: November 24, 2005 Posts: 635 Comments: 26556
1031. LargoFl
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Quoting emguy:


The everglades are "bonus ocean" for a storm. For example...Hurricane Andrew briefly intensified just inland...Tropical Storm Fay strengthened over the everglades...and her pressure dropped 12 MB while doing so.
I assure you that as hot as it has been here in south Florida, the water in the Everglades are nice and warm!! You can feel it in the air when winds are out of south and west into metro Broward county. I am in Weston.
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Quoting interpreter:
You are fooling yourself.

I am not fooling myself. Thats my idea, ive heard it from local stations, thats it. End of line.
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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 leaves over 300 miles until South Florida. I think landfall will be about 20 miles west of Miami as a cat 2.
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Quoting emguy:


The everglades are "bonus ocean" for a storm. For example...Hurricane Andrew briefly intensified just inland...Tropical Storm Fay strengthened over the everglades...and her pressure dropped 12 MB while doing so.


You left off one of the most amazing accomplishments I've seen over the Glades. Katrina. Intensified almost the whole way across.
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Quoting Neapolitan:
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.


I really hate that Justin Bieber is an analogy for sissy's. lol. He does have great hair does he not?
Member Since: February 28, 2012 Posts: 0 Comments: 66
Quoting sunlinepr:
Looks like the mountains of Hispaniola are already affecting Isaac

nope its dmin thats having an affect on convection but the inner core looks very good , lets see what recon finds
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1024. Dunkman
Quoting PublicAdjuster2:
Any chance this eventually hits New England?


Yeah, but by way of the Appalachian Trail.
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Good afternoon all..just lurking for a moment in between picking up the kids from school...this kept playing over in my mind..thought I'd share it with ya'll....The south wind will blow,
Where will Issac go?
The forcasters don't know,
because of the GOM low...
Just to lighten the mood guys..see ya'll this evening after they move the cone a smidgen more east..lol...
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Quoting Levi32:


Wait, you're agreeing with me today? Lol.
Just want to say I disagree with you saying in your tidbit that the surface circulation was ever just south of PR as per radar. At 50 miles out radar is looking at nearly 5,000ft up. You were looking more at like around 75-100 miles out which is 10,000 feet up. You were looking higher up than recon was. Any circulation you saw was not at the surface.

Also glad you finally shifted west lol.
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Quoting GTcooliebai:
Lets wait and see in the next frame, before we jump the gun.


Yep. Yesterday the euro started off NE of its previous track, and ended up going further west into the gulf. Levi may be right about these mountains jerking it around, but it'd be pretty hard for the models to correctly predict exactly how they will influence Isaac's path. The rest of the run will be interesting
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1020. 7544
Quoting Seflhurricane:
models now have a stronger system approaching South Florida so looks like if this trend continues hurricane watches may be needed for southern florida


looks like a big right shift comin on the next cone at 5 pm ?
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Quoting nrtiwlnvragn:


Look at this image and see where is lists SW 184 St.


Afternoon nrti. That was a very nasty place to be I am sure. Likely made my 20 mile inland adventure with Hugo's eye wall seem like a day at the McDonald's play ground and a Happy Meal.

Have a question for you, or anyone else interested. Isaac is a very large system and I do understand that it won't traverse near as much open water as Ike did; but what are the chances that we see an exaggerated surge based on the size of the storm. IE..If it is a TS could we see a Cat 1 surge or a Cat 1 and see a Cat 3 surge. Especially considering the area it will be approaching with the big bend likely "catching" water for some period of time.
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GIV back back up in the air to test the atmosphere again. should be in the 0Z models tonight.
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the more NW Isaac goes the more time over water he has the less land interaction and the threat to South florida increases
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This was from San Juan as Isaac passed South of Puerto Rico, he's a Big Boy!

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Quoting nrtiwlnvragn:


Northern Eyewall Never Again


Thanks, always wondered what that meant.
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Any chance this eventually hits New England?
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1013. emguy
Quoting GeorgiaStormz:


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


The everglades are "bonus ocean" for a storm. For example...Hurricane Andrew briefly intensified just inland...Tropical Storm Fay strengthened over the everglades...and her pressure dropped 12 MB while doing so.
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1012. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE SAN JUAN PR
208 PM AST FRI AUG 24 2012

THE NATIONAL WEATHER SERVICE IN SAN JUAN HAS EXTENDED THE

* FLASH FLOOD WARNING FOR...
THE FOLLOWING MUNICIPALITIES

IN PUERTO RICO
ARROYO
MAUNABO
PATILLAS

* UNTIL 345 PM AST

* AT 206 PM AST...RUNOFF FROM PREVIOUS HEAVY RAINFALL HAS RESULTED IN
SHARP RISES ON SMALL STREAMS AND RIVERS ACROSS THESE MUNICIPALITIES...
ESPECIALLY ACROSS THE MAUNABO AND PATILLAS AREA. MOTORISTS DRIVING
ALONG FLOOD PRONE AREAS SHOULD EXERCISE EXTREME CAUTION. MOVE TO HIGHER
GROUND IMMEDIATELY AND NEVER TRY TO CROSS A FLOODED ROADWAY.

LAT...LON 1796 6606 1809 6606 1810 6606 1810 6602
1806 6600 1806 6596 1803 6592 1803 6589
1802 6588 1803 6587 1801 6585



MARTINEZ

ADDITIONAL INFORMATION CAN BE FOUND AT /USE LOWER CASE LETTERS/:
HTTP://WWW.WEATHER.GOV/SANJUAN
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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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About

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