Isaac lashing the Keys; an eyewall is building

By: Dr. Jeff Masters , 3:48 PM GMT on August 26, 2012

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Tropical Storm Isaac is steadily organizing as it lashes the Florida Keys with heavy rain and tropical storm-force winds. Sustained winds of 44 mph and 41 mph have been observed at Molasses Reef and Sombrero Key, respectively, this morning. Radar out of Key West shows an increase in spiral banding, and the beginnings of an eyewall. An Air Force Hurricane Hunter aircraft completed its first pass through the center of Isaac near 11:30 am EDT, and did not find the pressure had fallen, or that the peak winds had increased. Infrared and visible satellite loops show that Isaac is a large and increasingly well-organized storm. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is quite good and increasing to the north, but is lacking elsewhere. Moderate wind shear and dry air to the south are interfering with heavy thunderstorm development on Isaac's south side. Heavy rains from Isaac are lingering over Haiti and the Dominican Republic; flash floods in Haiti from Isaac's torrential rains killed at least four people.


Figure 1. Morning reflectivity image from the Radar out of Key West radar shows the northwest section of an eyewall beginning to form to the southeast of the city.

Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs have diverged significantly, and we can no longer be confident we know where Isaac will make landfall on the Gulf Coast. One camp of models, the UKMET and ECMWF, predict that a trough of low pressure moving across the Southeast U.S. will be strong enough to turn Isaac north to a landfall in the Florida Panhandle. The other set of models, the GFDL, GFS, and HWRF, predict the trough will bypass Isaac, and a ridge of high pressure will build in and force Isaac to a landfall over Louisiana. The official NHC forecast averages out these two extremes, calling for a landfall midway between the two solutions. Odds are, one of the two model solutions will turn out to be the correct one, and the NHC will be forced to make a substantial adjustment in their forecast track to the east or the west. Isaac has the potential to drop torrential rains capable of causing serious flooding and drought relief over the South. The latest 8-day precipitation forecast from the GFS model calls for 10 - 20 inches of rain over Southeast Louisiana, where it predicts Isaac will make landfall. The ECMWF model, however, these heavy rains will fall more over the Florida Panhandle, Alabama, and Georgia.


Figure 2. A hurricane forecaster's dilemma: which set of models is correct? The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs have diverged significantly. Our two top models--the GFS and ECMWF--have 72-hour forecasts that are about 350 miles apart. The ECMWF forecast is not shown here, but lies just to the west of the UKMET forecast (white line.)

Intensity forecast for Isaac
Isaac survived passage over Hispaniola and Cuba relatively intact. It's large size aided this. Isaac is over very warm waters of 31°C (88°F) with high total heat content in the Florida Straits, but is encountering moderate wind shear of 10 - 15 knots due to upper-level winds out of the southwest. This shear is predicted to relax to the light range tonight as an upper-level anticyclone becomes established over the storm. This should allow for more substantial intensification after Isaac passes the Florida Keys. However, the total heat content of the ocean decreases for Isaac Monday morning as it encounters a relatively cool ocean eddy in the Southeast Gulf of Mexico. If Isaac takes a more westerly track, passing due south of the Central Louisiana coast, the storm will encounter a modest warm eddy, which would aid intensification. The intensify forecasts from the various models are very divergent. The latest 06Z (2 am EDT) run of the GFDL model keeps Isaac as a strong tropical storm until landfall in Louisiana. Isaac will undergo rapid intensification into a Category 3 hurricane as it hits New Orleans, says the latest 06Z (2 am EDT) run of the HWRF model. The ECMWF model has Isaac as a strong Category 2 storm with a central pressure near 950 mb as it hits near the Alabama/Florida border.

Comparing Isaac with Ike of 2008
The current situation with Isaac is similar in some ways to that of Hurricane Ike of 2008. Ike spent considerable time over Cuba, weakening from a Category 4 to a Category 1 storm. The storm couldn't put its energy into building a strong inner core, but it was able to build up its outer rainbands that were over very warm waters. This resulted in a major expansion of its wind field, with tropical storm-force winds extending out 275 miles from the center at one point. Ike was able to intensify into a Category 2 storm on its path towards Texas, and had an unusually low pressure for a Cat 2 storm with 100 mph winds--944 mb. That's a central pressure more typical of a Category 3 storm, but Ike could only manage Category 2 winds, since it had such a large chunk of the atmosphere to keep spinning. With Isaac's TS winds already extending out to 205 miles, maybe we'll see another Ike-type situation as it intensifies--the storm will have an unusually low pressure in order to keep a huge wind field spinning, but never make it above Category 2, since it will take so long to spin up such a large wind field.

Storm surge forecast for Isaac
Isaac is a very large storm, with tropical storm-force winds that extend out 205 miles from the center. For comparison, Hurricane Katrina at landfall had tropical storm-force winds that extended out 230 miles from its center. Isaac's large size will enable it to set a large area of the ocean into motion, which will generate a large storm surge once the storm approaches land on the Gulf Coast. The latest 3:30 am EDT Integrated Kinetic Energy analysis from NOAA's Hurricane Research Division put the destructive potential of Isaac's winds near 0 on a scale of 1 to 6, but the destructive potential of Isaacs's storm surge was 2.1 on a scale of 1 to 6. A 2008 paper by Irish et al., The influence of storm size on hurricane surge, found that large storms like Isaac are capable to delivering a 30% larger storm surge to the coast than a smaller storm with the same maximum wind speeds. The angle with which the storm hit the coast is important, too--a storm moving due north or slightly east of north will deliver a storm surge about 10% greater than a storm moving NNW or NW. Consult our Storm Surge pages for detailed information on what the risk is for the coast. I expect that Isaac's storm surge will be about 30% higher than the typical surge one would expect based on the maximum wind speeds.

Invest 97L off the coast of Africa
A tropical wave (Invest 97L) is located about 650 miles west of the Cape Verde Islands off the coast of Africa. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 50% chance of developing by Tuesday morning. None of the reliable models foresee that 97L will be a threat to the Lesser Antilles Islands. However, both the GFS and ECMWF models predict that a tropical wave that has not yet emerged from the coast of Africa may develop late this week, and potentially take a more westward track towards the Lesser Antilles, arriving around September 2.

Angela Fritz will have a new post here by 6 pm EDT. For the next few days, I plan to do the morning blog post, and Angela will be doing the late afternoon post. I'm in Atlanta to help out The Weather Channel with their on-air hurricane coverage, and will be on either in the afternoon or evening on Sunday, Monday, and Tuesday.

Jeff Masters

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TS Isaac about to become a big threat. Storm is growing.

Link
Member Since: Posts: Comments:
1325. DirtDan
Quoting NICycloneChaser:
I think that just about everybody here would be happy to agree that Isaac will be at least Cat 2 at landfall.

I've posted this before (before Irene last year), but Cat 2 Ike did this:



This doesn't need to be a major to wreak havoc. Everyone in it's path needs to remember this.



I remember that photo of Ghilcrist very well. Absolutely stunning yet tragic.
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Isaac+Gulf= Uh Oh
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Quoting Charliesgirl:
The reason is you need that time to evacuate. Schools will be closed if evacations are suggested/ordered where you live. It takes 2-3 days to evacuate NOLA for example.
Our schools in Santa Rosa County Florida are closed Tuesday and possibly Wednesday. (Gulf Breeze, Navarre Beach).
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1322. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 39702
1321. HrDelta
Quoting Charliesgirl:



Absolutely. It looks like they kicked our anthill.


Your ants are marching out?
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Quoting ProgressivePulse:

B. Center Fix Coordinates: 24°01'N 81°43'W (24.0167N 81.7167W)


Running a lil port of track.
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1319. Grothar
Isaac already has that classic look, which is remarkable from just a few hours ago.

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1318. yoboi
Quoting presslord:
well...in all fairness to BP....much of the oil can now be found inside fish, shrimp and oysters...along with much of the Corexit...


yep i fried some shrimp the other night ya don't even need any cooking oil just throw them in the pot and bamm.....fried shrimp
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When does the Euro run again?
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Quoting leftlink:
My previous post of the center of circulation as suggested by radar was a bit too far southwest. Here is a corrected version, as of 3pm. As you can see the center is just about to reach its closest pass to key west (about 20 miles away). Moving just north of WNW. Winds should shift in next 20 minutes:



Center is still much larger. With in the larger circulation their are smaller little circulations rotating around.
Remember how big Wilma's center/eye was when it it Florida. It was huge.

Centers don't have to be small points. Some tropical systems have larger broader centers.

Very large center/eye with Wilma as it crosses S. Fl.
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Starting to look very dangerous.
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1314. pottery
Quoting presslord:
well...in all fairness to BP....much of the oil can now be found inside fish, shrimp and oysters...along with much of the Corexit...

Well, yes!

But we don't want to go there......

:):))
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Quoting cajunkid:


Dude...Microbes have eaten all that oil.

Light crude does not last long outside a container, much less in salt water.


do what?
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1311. GBguy88
There was a large area of submerged oil found in Perdido Pass in May. I'd post the link, but that's against the rules, yes? Easily found on Google.
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Member Since: Posts: Comments:
Yall scared of this little ol' thing?




Sarcasm.

hehe...

about one third of the system is still dry and cut off by Cuba, just wait till all that gets over the Gulf.

This is probably bigger than Ike when it fills out...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting SykKid:


dry air exist though


The dry is been pushed by the storm. Isaac is moinstening his environment.
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Quoting maeko:
TWC said Dr. Masters would be on for the 'duration'. Wow! Is this the first time he's done this?
Anything would be better than what they've got now, except for Cantore. How I miss John Hope.
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1306. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 39702
B. Center Fix Coordinates: 24°01'N 81°43'W (24.0167N 81.7167W)
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1304. BlxMS
OUCH, but many thanks Barbanz
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Quoting mojofearless:
Just went to get extra dog food and cigarettes (all our other supplies just stay in place or get rotated annually), and wow - NOLA is shifting into high gear. Gas stations have lines, and everybody is stocking up.



Absolutely. It looks like they kicked our anthill.
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his south side is fighting the cuban dry air pretty well
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting dmh1026:
Squalls underway in Estero, FL right now..


Hows it doing? I got a friend who lives west of 41 and south of corkscrew.
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Quoting cajunkid:


Dude...Microbes have eaten all that oil.

Light crude does not last long outside a container, much less in salt water.

It wasn't all light crude. As much spilled, plenty of heavier stuff came out as well.
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1299. HrDelta
Quoting Levi32:
Core winds are not impressive yet, but pressures are falling.

More recon plots here



The map does show winds between 65-70 on there. They will have to up the strength just a touch.
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1298. pottery
Quoting GBguy88:


I found a softball sized tar ball a couple of weeks ago on Pensacola Beach...broke it open and the inside was still very gooey and strongly scented. If you're paying attention, you can see other smaller tarballs that still pepper the sand here and there. It's not gone.

Yeah, I am sure there are tar-balls around.
Probably always have been some, and likely there will always be some.
But the way the thing was quoted it sounded like thousands of barrels of oil are going to come washing over the beaches and into the ecology....

That is a very unlikely scenario.
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well...in all fairness to BP....much of the oil can now be found inside fish, shrimp and oysters...along with much of the Corexit...
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1296. bappit
Quoting TxGrandma:
Link

It was indeed in that spot....here's an article about it:

http://articles.cnn.com/2008-09-18/us/ike.last.ho use.standing_1_yellow-house-pam-adams-new-house?_s =PM:US

Not found.
Member Since: Posts: Comments:
Is it just me, or are some of these model runs starting to look a bit doomsdayish? Particularly the HWRF.



*DISCLAMER* This is just one model run and not the official forecast to those lurking.
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1294. barbamz

Last Euro.
Member Since: October 25, 2008 Posts: 55 Comments: 6079
Quoting BlxMS:


Sorry for the amateur question, but been busy and just have a few mins available now...What time was the latest Euro released,,,when is the next and does anybody have a real quick link to the latest Euro...Thanks for the help


Norcross on twc stated that all of the EURO runs were not complete, but from what he was seeing they were still vastly different than the GFS
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Quoting TropicalAnalystwx13:
Tropical Cyclone Heat Potential is not below average in the Gulf this year. It is average to above average.

I stand corrected!!The data speaks for itself,doesn't it?
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1290. KEEPEROFTHEGATE (Mod)
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Isaac continues to organize.

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54mph gust in my location right now! Very intense cell just popped over Coral Gables out of nowhere. Torrential sideways rain. Trees bending towards the west. Wow.
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1287. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 39702
Quoting pottery:

That's why I thought that Dr. Masters statement (as quoted here on the blog) was a little strange......

What oil ???


I've fished from Sabine WMA to Black Bay and haven't seen or heard anyone seeing any for a year now.
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Quoting MiamiHurricanes09:
Pressure down to 992mb.

Dropsonde released in the eye of Isaac has brought back an MSLP of 992mb with 7mph of surface winds. The splash location was 24.02N 81.69W. Isaac appears to be intensifying at about 2mb per hour, which would technically qualify as rapid intensification.


000
UZNT13 KNHC 261906
XXAA 76198 99240 70817 08141 99992 27810 23006 00572 ///// /////
92620 25021 24007 85364 22030 18508 88999 77999
31313 09608 81846
61616 AF309 2109A ISAAC OB 15
62626 EYE SPL 2402N08169W 1849 MBL WND 24507 AEV 20802 DLM WND 23
005 991842 WL150 24006 084 REL 2402N08170W 184651 SPG 2402N08170W
184807 =
XXBB 76198 99240 70817 08141 00992 27810 11850 22030 22842 /////
21212 00992 23006 11923 24007 22884 26001 33855 19505
31313 09608 81846
61616 AF309 2109A ISAAC OB 15
62626 EYE SPL 2402N08169W 1849 MBL WND 24507 AEV 20802 DLM WND 23
005 991842 WL150 24006 084 REL 2402N08170W 184651 SPG 2402N08170W
184807 =
;





here we go
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1284. bappit
Quoting cajunkid:


Dude...Microbes have eaten all that oil.

Light crude does not last long outside a container, much less in salt water.

Yeah, it just leaves tar balls.
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St. Charles Parish Schools have closed Mon-Weds. as of now.
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Quoting TropicalAnalystwx13:

I don't see why they would cancel school along the Gulf Coast tomorrow. They didn't the day before Irene here last year...which was exactly a year ago actually. You won't have school Tuesday, Wednesday, and maybe even Thursday though. I can guarantee that.
The reason is you need that time to evacuate. Schools will be closed if evacations are suggested/ordered where you live. It takes 2-3 days to evacuate NOLA for example.
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Quoting leftlink:
My previous post of the center of circulation as suggested by radar was a bit too far southwest. Here is a corrected version, as of 3pm. As you can see the center is just about to reach its closest pass to key west (about 20 miles away). Moving just north of WNW. Winds should shift in next 20 minutes:

Almost looks like the center is moving nnw
Member Since: Posts: Comments:
1280. GBguy88
Quoting pottery:

That's why I thought that Dr. Masters statement (as quoted here on the blog) was a little strange......

What oil ???


I found a softball sized tar ball a couple of weeks ago on Pensacola Beach...broke it open and the inside was still very gooey and strongly scented. If you're paying attention, you can see other smaller tarballs that still pepper the sand here and there. It's not gone.
Member Since: Posts: Comments:
1279. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 39702
Pressure down to 992mb.

Dropsonde released in the eye of Isaac has brought back an MSLP of 992mb with 7mph of surface winds. The splash location was 24.02N 81.69W. Isaac appears to be intensifying at about 2mb per hour, which would technically qualify as rapid intensification.

000
UZNT13 KNHC 261906
XXAA 76198 99240 70817 08141 99992 27810 23006 00572 ///// /////
92620 25021 24007 85364 22030 18508 88999 77999
31313 09608 81846
61616 AF309 2109A ISAAC OB 15
62626 EYE SPL 2402N08169W 1849 MBL WND 24507 AEV 20802 DLM WND 23
005 991842 WL150 24006 084 REL 2402N08170W 184651 SPG 2402N08170W
184807 =
XXBB 76198 99240 70817 08141 00992 27810 11850 22030 22842 /////
21212 00992 23006 11923 24007 22884 26001 33855 19505
31313 09608 81846
61616 AF309 2109A ISAAC OB 15
62626 EYE SPL 2402N08169W 1849 MBL WND 24507 AEV 20802 DLM WND 23
005 991842 WL150 24006 084 REL 2402N08170W 184651 SPG 2402N08170W
184807 =
;
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Quoting gustaveye:


i would think as soon as a hurricane warning goes up for your parish that school will be cancelled....some parishes have already cancelled school


I would imagine mine will cancel if we have a warning
Member Since: June 17, 2011 Posts: 11 Comments: 6539
1276. guygee
Quoting Levi32:
Interesting that the group of CMC members, of all things, don't strengthen Isaac beyond Cat 2 in general.
Yeah, doesn't the CMC usually have problems with convective feedback and overestimating storm intensities. Colossal Mess Creator.
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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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