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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1111. GetReal
Quoting RTSplayer:


How do you get that so quickly?

The site Wunderground links to is usually another hour behind people posting individual frames, and it doesn't have as much detail...

Can you provide a link to the hosting site please?



Wrong run sorry for the mix up...
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1110. wpb
watvhes are due 48 hour in advance. models show very close to se coast of fla upper keys in 48 hours.
????think they will post at 6pm
??tropical storm watch or hurricane watch??
anyone have a good answer
Member Since: May 28, 2011 Posts: 0 Comments: 573
Quoting Levi32:


The height was 6000 feet based on the 0.5 degree radar angle. You could tell by the low-level banding showers that it was a lower level circulation there yesterday, while the mid-level rotation was quite clear on the outer fringes of the radar which were over the 700mb level to the south. There is more to radar interpretation than just the beam height.
Nope, not even close.

Look here.

EDIT: I see you edited your post lol. But previously this quote said at 130-150 miles with 0.5 tilt it was 6,000 ft. Reality is it was about 14,000 ft.
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1108. Dunkman
Quoting GTcooliebai:
And how do we know if this model isn't out to lunch? Does anyone know if they got the Gulf Stream Data into this model?


Yes we share all of our data with the Euro. I mean you can write off the best model we have for forecasting tropical cyclone track but that seems unwise.
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Quoting chrisdscane:



lol that may be overding it a bit rofl


Mark my words, this will skim the north side of Cuba. This gives the storm about 24 hours until it hits sofl! I think it will be a weak cat 2. I also think that forward motion will slow as well, giving it more time in the straits.
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Euro is very, very consistent that Isaac will become a potent Hurricane in the Gulf. Will it happen? Remains to be seen. Often, the Euro exaggerates with strength.. but that is usually when it is 240 hours out. Conditions do certainly support this scenario but the question is - will it utilize it?
Member Since: July 8, 2005 Posts: 259 Comments: 24574
In the summertime the water in the Everglades is almost steaming hot. it is shallow and very hot and very flat.

Like previously said, storms increase in strength when crossing The "Glades...

also Irene in 1999 and someone already mentioned TS Faye, she got her "act" together over that steamy water.

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1104. FOREX
Quoting floridaboy14:
looks like you eastcasters should take a look at the euro. even further west


I'm going with the GFS.
Member Since: August 17, 2011 Posts: 0 Comments: 2335
Quoting HoustonTxGal: Well, then Gulfport is safe for now.


Maybe .... Maybe not..
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18:21:30Z 17.100N 70.383W 842.2 mb
(~ 24.87 inHg) 1,515 meters
(~ 4,970 feet) 1004.0 mb
(~ 29.65 inHg) - From 156° at 67 knots
(From the SSE at ~ 77.0 mph) 15.0°C*
(~ 59.0°F*) 15.0°C*
(~ 59.0°F*) 70 knots
(~ 80.5 mph) 48 knots
(~ 55.2 mph)
Member Since: August 18, 2009 Posts: 0 Comments: 460
1101. HCW
Expect the 5pm track from the NHC to shift east 20 to 30 miles
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1100. mrjr101
Quoting Kowaliga:


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



How about intensity models to the shredder? NHC should really keep intensity forecast to themselves.
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12z euro is biloxi, MS
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Member Since: February 3, 2010 Posts: 0 Comments: 755
NHC has respectable company out there but only a couple.

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Product: Air Force Tropical RECCO Message (URNT11 KNHC)
Transmitted: 24th day of the month at 18:12Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number: 09
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 12
Observation Number: 01

Mandatory Data...

Observation Time: Friday, 18:10Z
Radar Capability: Yes
Aircraft Altitude: Below 10,000 meters
Coordinates: 17.4N 69.8W
Location: 75 miles (120 km) to the S (175°) from Santo Domingo, Dominican Republic.
Turbulence: None
Conditions Along Flight Route: In the clear
Pressure Altitude: 1,520 meters
Flight Level Wind: From 150° at 50 knots (From the SSE at ~ 57.5 mph)
- The above is a spot wind.
- Winds were obtained using doppler radar or inertial systems.
Flight Level Temperature: 14°C
Flight Level Dew Point: 14°C
Weather (within 30 nautical miles): Thunderstorm(s)
850 mb Surface Altitude: 1,471 geopotential meters

Optional Data...

Estimated Surface Wind: From 150° at 40 knots (From the SSE at ~ 46.0 mph)

Remarks Section...

Surface Wind Speed (likely by SFMR): 42 knots (~ 48.3mph)
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Quoting RTSplayer:


Yeah, but look at the finger of the ridge ahead of it. It should take a western jog on the next frame or two...

Nope central Florida.
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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 leave over 300 miles until South Florida. I think landfall will be about 20 miles west of Miami as a cat 2.


So... landfall will be in the everglades somewhere?
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Of course the NHC will stick with the Euro when all the guidance is over FL now. This could be bad for the NHC and their credibility.

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looks like you eastcasters should take a look at the euro. even further west
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Keep in mind I'm watching the wv loop on a kindle.....but I see the storm being pushed from the back by the feature in the Atlantic while a front is diving down toward FLA from the NW. How can the storm penetrate that? Won't it work around that and isn't there a high moving in across Fla from the E to W? Lots of factors and timing to play out...
Raining off and on now S of NO.
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Quoting WxGeekVA:
Euro 12Z still west... Eastcasters are jumping the gun I think.

And how do we know if this model isn't out to lunch? Does anyone know if they got the Gulf Stream Data into this model?
Member Since: August 31, 2009 Posts: 0 Comments: 5628
1089. Chema44
"A mal Tiempo buena Cara" Para los que no lo han visto he aquí el video desde La Guancha en Ponce, tenemos a Chema Weather Cantore, Jasleen Ginelle, Janet Ortiz, Joel Lugo, Julio Santos, El Corillo del CMC con nuestras camisas. Ada que lo disfrutes.

http://www.youtube.com/watch?v=8sqL_K7K1a8&featur e=youtu.be
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1088. pottery
Quoting yoboi:


my fav words to hear...

I don't get it.....

:):))
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Quoting CJ5:
There are a lot of unprotected people in Port au Prince and Isaac appears to be heading right for it. Sad.


yup
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1086. BigTuna
Quoting FLHurricaneHunter:
4 flights per day on JetBlue from Fort Lauderdale-Hollywood International
He's a big boy though; he'll need to purchase at least 2 seats.
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1085. OneDrop
Quoting wpb:
good recon data very soon
Nice avatar, I miss McCrays BBQ in WPB since I moved north to Ormond.
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Is central Cuba as damaging to storms (mountainous) as eastern Cuba and Haiti? Or more similar to Florida (flatter) in that storms can cross without losing as much intensity?
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Quoting coffeecrusader:
12z Euro has shifted even further west than last run and has Isaac making a run at New Orleans. Based on this I don't think NHC will change the track at 5pm infact they may move it a little more west.


96 hours 12z 8/24


96 hours 00z 8/24


Are these NEW?
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Firsthand Weather are now on FL
Member Since: May 23, 2012 Posts: 0 Comments: 4984
Quoting SFLWeatherman:
2PM


If it keeps a NW motion, wouldn't it pretty much cross all through Cuba and all the mountains? How would it survive that?
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Quoting WDEmobmet:
Jim Cantore arrived at Gulfport MS


Why? It's not even going there.

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1079. CJ5
There are a lot of unprotected people in Port au Prince and Isaac appears to be heading right for it. Sad.
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1078. GetReal
Quoting RTSplayer:


How do you get that so quickly?

The site Wunderground links to is usually another hour behind people posting individual frames, and it doesn't have as much detail...

Can you provide a link to the hosting site please?



Wrong run...
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Quoting ProgressivePulse:
17.500N 69.500W
SFMR
59 knots
(~ 67.8 mph)

That's pretty far from the center too.


Rain contaminated. Needless to say though that Isaac has a pretty large wind field.
Member Since: July 8, 2005 Posts: 259 Comments: 24574
Quoting StormJunkie:


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.


I think we have seen from past experience that size does matter, but I have not personally done a lot of research into surge. The references on this webpage may have that type of info.
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Quoting FLHurricaneHunter:
4 flights per day on JetBlue from Fort Lauderdale-Hollywood International


LMAO!! he better book one because a lot of folks may be trying to get out and seats may be few and far between
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1074. Dunkman
120h Euro Mobile, AL landfall as a major.
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Quoting LargoFl:
GFS at 72 hours


uncool
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If the high from over the south develops as strong as forecasted by the GFS Mississippi and Louisiana can rest and go have a beer this weekend. Westcasters I do not see any logic in your forecast. Keeping an eye on it is the best policy, but I am feeling much better now that it is trending east.

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12z Euro has shifted even further west than last run and has Isaac making a run at New Orleans. Based on this I don't think NHC will change the track at 5pm infact they may move it a little more west.


96 hours 12z 8/24


96 hours 00z 8/24
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Quoting Dunkman:


That is yesterday's run.


NO it isn't!
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1069. Levi32
Quoting cat7hurricane:
Just want to say I disagree with you saying 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.


The height was 6000 feet based on the 0.5 degree radar angle. You could tell by the low-level banding showers that it was a lower level circulation there yesterday, while the mid-level rotation was quite clear on the outer fringes of the radar which were over the 700mb level to the south. There is more to radar interpretation than just the beam height.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting GetReal:


Euro 12z back to NOLA...


How do you get that so quickly?

The site Wunderground links to is usually another hour behind people posting individual frames, and it doesn't have as much detail...

Can you provide a link to the hosting site please?
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Euro 12Z still west... Eastcasters are jumping the gun I think.

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Near Santo domingo


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Link

cool loop of isaac wrapping up.... takes a while to load
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1064. LargoFl
Quoting LargoFl:
GFS at 72 hours
sure looks like a hit there or right on the beaches
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Quoting HoustonTxGal:


If he can get a flight out of Miami.
LOL!
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2PM
Member Since: May 23, 2012 Posts: 0 Comments: 4984
1061. Dunkman
Quoting GetReal:


Euro 12z back to NOLA...


That is yesterday's run.
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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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