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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Q will it go to S FL
A. yes
B. no
I say yes
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Quoting WxLogic:
12Z CMC

Hmm... at least is consistent now.


That would be awful... the entire state and all the major metropolitan areas plus Okeechobee Lake which will eventually kill again.
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Quoting Bluestorm5:
Why are we talking about USA landfall when we should be worry if Isaac will be a hurricane or not before Haiti. If you look (and I mean LOOK) at this picture, you can see that 7,000 Haitians is living in this area trying to prepares for Isaac.



Thanks for picture. I was wondering how part of it might look.
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Good afternoon.

Blog update:

Tropical Tidbit for Friday, August 24th, with Video
Member Since: November 24, 2005 Posts: 635 Comments: 26647
No you guys are right... we are the bad guys

Aid given to Haiti
United States US 466,879,506
Canada CA 130,733,775
World Bank (emergency grant) 82,107,356
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Quoting LargoFl:
arent the french responsible for haiti? ask them what they are doing


I don't think so. I think we are the biggest givers of aid.

Even though are French Creole, we take more care of them than France.
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Did I just hear that Jim Cantore is in MObile, AL.
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Quoting HrDelta:


Looking at the picture, I have one simple question.

WTF is it doing?


isaac

wat r u doin?

isaac

stahp
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Haiti has been an independent country since 1804
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Quoting ftlaudweathermaster:
The GFS model run that came out just a couple of hours ago does have landfall in the Miami area.
this could be very serious..never been to miami..if a storm approaches from the south..is there going to be massive flooding from surge?
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Is Levi the weather expert? He must have a straight line to mother nature right? NOT.
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So this thing is now shifting enough to pull LA out of the cone? Just wondering if any of you think this could possibly stay West enough to affect any of LA? In SE Louisiana here......Lafayette area. Thanks
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Issac still needs to finish wrapping up the NW side of the circulation... a little bit of dry air may be wrapping in. Needs to fire convection in that area before it can really strengthen. Probably won't happen before landfall and we will see.
Member Since: July 6, 2005 Posts: 5 Comments: 580
Quoting Bluestorm5:
US government don't really cares for third world countries... that's the truth. Corruption and greed will makes that happened. Not trying to start political war on here so back on topic.

Link
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Quoting Methurricanes:
LOL, I was thinking the same thing.


Anyone can now go to Cuba. There are several charter flights operating out of FL. Just no commercial.
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Last question, what is the High in the central GOM going to do and when? How is that going to affect the track?
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Quoting LargoFl:
arent the french responsible for haiti? ask them what they are doing
Not since Mr. Boneparte.
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643. MTWX
Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.

Quoting indianrivguy:


no way.... we will see what the death toll is.


I completely agree indianrivguy! The US has a lot more ability to prepare for and recover from a Cat 5 than Haiti does for even a Tropical Storm!
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642. JeffM
Quoting SFLWeatherman:
Were is Levi??????


Probably putting together his report.
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Quoting Walshy:
wow 12+ inches of rain..going to be massive flooding
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640. FOREX
Quoting Bluestorm5:
US government don't really cares for third world countries... that's the truth. Corruption and greed will makes that happened. Not trying to start political war on here so back on topic.


Really?? America is the most giving country in the World. Where are all of the Muslim countries when Indonesia, a Muslim country has a tsunami? Nowhere to be found or heard of.
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I don't think Pat left enough Fresca behind for this bunch on the blog.....
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.
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No update from Levi in his blog yet.
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Jeff's synopsis of an eye trying to form between 2 and 4 today looking, as usual, spot on. Isaac through messing around in the daylight hours. I may be wrong, but I'm almost positive NBC will have someone reporting from Haiti tonight on the nightly news. Isaac's really revving up nicely now, hurricane strength+ not out of the question by four.
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Quoting flowrida:
What would happen to the tampa bay area if Issac was a cat 2 right off the coast, say 40 miles?


1.Tropical Storm-like conditions over the whole area with hurricane force gusts possible on the immediate coast, meaning mostly the barrier islands.

2. Heavy rains. The rainfall totals would depend on the forward speed of the storm. A faster moving hurricane would mean less rain, perhaps an average of four inches at most locations. A slower moving system could produce up to 8 or 9 inches in many locations.

3. A significant risk for tornadoes over much of the Florida peninsula, particularly ahead of the storm. After the center passes any given latitude this risk would drop. These tornadoes would be mostly small EF-0 and EF-1 twisters.

4. Some coastal flooding after the center passes to the north of a given latitude. How much would depend on the size of the storm and its forward speed. A smaller cyclone would produce less flooding, maybe 2 to 3 above normal tide levels, whereas a larger and slower-moving cyclone would produce maybe 4-5 feet above normal tide levels of surge.

All in all, a storm passing 40 miles offshore at Cat 2 strength would not produce widespread devastation but would be a nuisance. Again though, the most important factors in determining the exact impacts would be the size of the storm and its forward speed when it passes.
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Quoting Bluestorm5:
Only takes a Category One to cause 1,000 deaths in Haiti. That's more than 90% of hurricanes that will ever hit USA. This isn't all-American blog.


Doesn't even take a cat1.

2004
23%u201324 May: Torrential rains which pounded the south-east of Haiti during the night caused 1,232 deaths, 1,443 disappearances and 31,130 displaced persons.[9]Mapou[10][11] Belle-Anse with 432 dead, Bodary with 350 dead and Fonds-Verrettes with 237 victims, all located in the Sud-Est dpartement, were the places most badly hit.
The gravity of this situation led the interim government of Boniface and Latortue to declare Friday 28 May a day of national mourning.

10 September: Hurricane Ivan struck the southern peninsula and west coast, causing serious damage in several areas due to flooding.

18-19 September: Hurricane Jeanne crossed the western section of Haiti and the Artibonite, causing flooding which killed 1,870. In addition: 2,620 injured, 846 disappeared and 300,000 displaced. With more than 3,000 dead, Gonaves was the most seriously affected city.[12]


Source Wikipedia "List of Natural Disasters in Haiti".


I think the May storm was either an early TD or just a frontal boundary, but I don't remember...


All of this happened in just one year in a 4/5 month span...


It should also be noted that these events were obviously before the Earthquake or the 2005 season...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Everyone is surprised at the northwestern jog, even though the models have called for this from the start.

Link

Use the coast of Barahona in the SW corner of the Dominican as a reference point. Even the very first advisory places the track of Isaac within 75 miles of the peninsula.

Over time the track shifted onshore Barahona, then south of it again. Looks like he'll actually skim just south of there.
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IMO Isaac briefly jogged NW during the reorganization process of becoming stacked. It appears to me that he has resumed a w to wnw track for now, as steering would indicate.
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Quoting WxLogic:
12Z CMC

Hmm... at least is consistent now.


That's a strange track, CMC seems to be struggling with how to deal with all the different steering mechanisms. Then again it's hardly unusual for storms to make erratic movements.
Member Since: February 6, 2010 Posts: 0 Comments: 214
Quoting Seflhurricane:
very likely , would not be surprised if a hurricane watch is issued for the florida keys
ea

My guess is that they will wait til 5pm advisory because if they change the long term track and have more of an easterly track as you both are saying HW for keys SW FL and TSW for rest of South Florida. There is an outside possiblity of HW for S Florida.

I think on Tuesday this is what one forecaster said from central Florida TV station
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Quoting LargoFl:
arent the french responsible for haiti? ask them what they are doing


Yep, they do nothing
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Where is Levi??????
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The GFS model run that came out just a couple of hours ago does have landfall in the Miami area.
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I am located in Naples, Fl not far from the beach. I have been keeping an eye on this storm. I have lurked here for many years during hurricane seasons and learned lots too. I've always enjoyed reading this forum.
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Quoting WhoDat42:
Current forecast calls for me easily exceeding 200 on the ignore list by landfall next Wed am.
\

Thats okay, youre a saints fan
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WOW lol
Quoting WxLogic:
12Z CMC

Hmm... at least is consistent now.
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Quoting HrDelta:


I constantly worry about Haiti. As I have said before, I would prefer a stronger storm striking us, if it means Haiti doesn't get more than a menial amount of rain and wind.
arent the french responsible for haiti? ask them what they are doing
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Member Since: August 2, 2010 Posts: 21 Comments: 9814
Quoting TomballTXPride:


Looking at the picture, I have one simple question.

WTF is it doing?
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619. bwi
Look at the low level inflow well out west (and a little south) of the storm at the buoy at 15n 75w.

This is an impressive tropical storm in my opinion to be moving air from west to east like that out front -- large wind field. The mountains of Cuba may disrupt the inner core, but there's a lot of atmosphere in motion now, and that won't dissipate easily.

10:50am
Wind Direction (WDIR): NW ( 310 deg true )
Wind Speed (WSPD): 15.5 kts
Wind Gust (GST): 17.5 kts

08 24 9:50 am WNW 17.5 19.4 4.6 8 4.8 N 29.72 +0.03 83.1 82.8 76.5 - - -
08 24 8:50 am WNW 17.5 19.4 4.3 5 4.6 NNW 29.72 +0.03 83.1 82.8 76.5 - - -
08 24 7:50 am NW 17.5 21.4 4.3 5 4.5 NNW 29.70 +0.03 82.9 82.8 76.3 - - -
08 24 6:50 am WNW 15.5 19.4 3.6 7 4.5 NNE 29.68 +0.02 82.6 82.8 76.3 - - -
08 24 5:50 am WNW 15.5 17.5 3.9 5 4.5 NNW 29.69 -0.01 82.4 82.8 75.7 - - -
08 24 4:50 am WNW 17.5 21.4 3.3 8 4.3 ENE 29.67 -0.05 82.4 82.8 76.1 - - -
08 24 3:50 am W 17.5 19.4 3.3 7 4.4 ENE 29.66 -0.07 82.0 82.8 75.9 - - -
08 24 2:50 am WNW 15.5 19.4 3.3 8 4.7 ENE 29.70 -0.04 82.2 82.9 75.9 - - -
08 24 1:50 am W 13.6 17.5 3.3 8 4.7 ENE 29.72 -0.04 82.2 82.9 75.6 - - -
08 24 12:50 am WNW 13.6 17.5 3.0 7 4.4 E 29.73 -0.03 82.4 82.9 74.7 - - -
08 23 11:50 pm WNW 15.5 19.4 3.0 7 4.6 NE 29.73 -0.02 82.4 83.1 74.1 - - -
08 23 10:50 pm W 11.7 13.6 3.0 7 4.7 ENE 29.76 +0.01 82.6 83.1 74.1 - - -
08 23 9:50 pm WNW 9.7 11.7 3.3 8 4.9 ENE 29.76 +0.01 82.4 83.3 74.3 - - -
08 23 8:50 pm WNW 11.7 13.6 3.3 7 4.9 ENE 29.75 +0.00 82.2 83.5 74.8 - - -
08 23 7:50 pm NW 11.7 13.6 3.3 7 5.2 ENE 29.75 +0.00 82.4 83.7 75.0 - - -
08 23 6:50 pm NNW 9.7 11.7 3.3 7 5.2 ENE 29.75 -0.02 82.6 83.8 74.5 - - -
08 23 5:50 pm NW 7.8 9.7 3.3 7 5.2 E 29.75 -0.04 82.9 84.0 73.9 - - -
08 23 4:50 pm NNW 7.8 7.8 3.6 7 5.5 E 29.76 -0.06 83.7 84.2 74.3 - - -
08 23 3:50 pm NNW 5.8 7.8 3.6 7 5.2 ENE 29.77 -0.06 83.5 84.6 74.5 - - -
08 23 2:50 pm N 3.9 5.8 3.3 7 5.3 E 29.79 -0.05 83.7 84.7 73.6 - - -
08 23 1:50 pm NNE 1.9 3.9 3.9 7 5.4 E 29.82 -0.04 83.3 84.4 73.6 - - -
08 23 12:50 pm NNE 3.9 3.9 3.6 7 5.3 E 29.83 -0.04 83.1 84.0 73.6 - - -
08 23 11:50 am NE 5.8 7.8 3.6 7 5.5 E 29.84 -0.03 83.1 83.5 74.3 - - -
08 23 10:50 am NE 3.9 5.8 3.9 7 5.3 ENE 29.85 -0.01 83.3 83.1 74.1 - -
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Quoting DVG:


At least it's about current weather, rather than some canned programming.


True.
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It going to be in TX lol jk
Quoting mobhurricane2011:
New Euro comes out shortly right? I'm guessing we will see a east shift, but who knows
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616. FOREX
Quoting Stormchaser121:

ERUO model still saying western gulf?? I still think its correct.


the euro hasn't run yet. that is last nights model.
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Isaac doesn't look particularly great right now. Recon will probably find 55mph or so IMO.

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Current forecast calls for me easily exceeding 200 on the ignore list by landfall next Wed am.
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12Z CMC

Hmm... at least is consistent now.
Member Since: August 14, 2008 Posts: 4 Comments: 4972
Quoting RobbWilder:


rarely ever at the intermediate advisories. Always the 5's and 11's. It was designed to play to the news cycles. 6am 12pm 6pm and 11pm news.



What? they issue warnings and watches all the time at the intermediate updates.
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Quoting TropicalAnalystwx13:

What I'm saying is that, yes, it's a sad situation for Haiti. But, I doubt people from that area are on the blog. People along the Gulf Coast could be dealing with a major hurricane in 5 days, and this could be much worse for the USA than it is for Hispaniola.


no way.... we will see what the death toll is.
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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.