Isaac lashing the Keys; an eyewall is building

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

Share this Blog
44
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1826 - 1776

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45Blog Index

1825. sar2401
Quoting stormhank:
Is it possible Isaac could still come inland near pensacola // mobile?? I see the euro model didnt budge takin Isaac into this area


Yes. You are still in the cone, and at least two reliable models take Isaac into the Panhandle/Mobile. This is not going to be resolved with the 5 pm update, at least not today.
Member Since: Posts: Comments:
1823. dmh1026
Quoting angelafritz:
I like the new music choices on TWC for Local On the 8s. 24 hour coverage of an approaching hurricane is very difficult, especially 3-5 days in advance of landfall, when the only changes we really see are from Hurricane Hunters and every three hours in the NHC advisories. Personally, I've enjoyed watching the TWC coverage of Isaac. I like seeing the conditions on the beaches where the reporters are located, and I like seeing the different ways that Bryan and his team explain current observations and forecasts to the viewers.

By the way, Doc is on around 4:30 EDT, so tune in! :)

I think TWC has done a very god job! I agree Angela!
Member Since: Posts: Comments:
No human pathogens are known to survive in beer....just sayin'
Member Since: Posts: Comments:
Quoting timmoss:


I was going to say the same thing--I was In NOLA through the storm and the aftermath (sold my car the week before--that was a problem!). People were absolutely told to go to the Dome for shelter. Also, even with the "mandatory" evacuation, certain people were asked to stay--medical personnell and hotel workers--there were a LOT of tourists trapped in the city who couldn't get out.


In the Saturday press conference people were told not to use the Dome as shelter. It was opened Sunday because so many people went there.

Mayor Ray Nagin called the Superdome's opening as a shelter a "last resort." He didn't have to explain that to the hundreds of New Orleanians gathered about Poydras Street's sidewalks Sunday before noon.

http://www.nola.com/hurricane/katrina/stories/DOM E29.html


Member Since: Posts: Comments:
Ok, dad can't find the briefing with Gov Jindal...is it on TV????
Member Since: Posts: Comments:
Quoting angelafritz:
I like the new music choices on TWC for Local On the 8s. 24 hour coverage of an approaching hurricane is very difficult, especially 3-5 days in advance of landfall, when the only changes we really see are from Hurricane Hunters and every three hours in the NHC advisories. Personally, I've enjoyed watching the TWC coverage of Isaac. I like seeing the conditions on the beaches where the reporters are located, and I like seeing the different ways that Bryan and his team explain current observations and forecasts to the viewers.

By the way, Doc is on around 4:30 EDT, so tune in! :)
Yeah, the music choices ACTUALLY mention weather and hurricanes. People actually might hate on TWC a little TOOmuch.
Member Since: Posts: Comments:
Quoting stormhank:
Is it possible Isaac could still come inland near pensacola // mobile?? I see the euro model didnt budge takin Isaac into this area

The latest European model did budge. Previous run showed Pensacola. Lastest run shows Mobile.
Member Since: Posts: Comments:
Quoting airmet3:


I believe Rita and Katrina were both well established hurricanes at this point.



Rita was just developing.
Member Since: Posts: Comments:
1816. angiest
Quoting 1900hurricane:
This blog is moving at ludicrous speed. Been a long time since I've seen it move this fast.


Are we going to plaid?
Member Since: Posts: Comments:
1815. JGreco
Quoting GetReal:



Time and distance is running out quickly, and decisions need to be made by officials relying upon the NHC.



This sucks...really need to know if pensacola-Fort walton Beach-Destin out of the woods....
Member Since: Posts: Comments:
1814. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 33236
Quoting duranta:


People were told to bring supplies for three days. If you recall, folks were there much longer. I'll re-fight it with you here and now.


PLEASE calm down..this little argument was started when Bobsled27 made a disguised racial slur...now the blog is rolling so fast you are all misconstruing STUFF...so just stop now please.
Member Since: Posts: Comments:
Quoting TomballTXPride:
Gotta remember guys, we aren't talking about 5 days out. This is 72 hours, perhaps even less. It's crunch time, and I'm certain the authorities are aware of the dire situation.


Thats is curtain glad I dont have to make that kinda of call talk about stress
Member Since: Posts: Comments:
Thunder in a tropical system rain band is an indication of strengthening right?
Member Since: Posts: Comments:
Quoting yoboi:


press where is junkie at this eve???


driving to P cola...as is our SAR team from Little Rock
Member Since: Posts: Comments:
Quoting yoboi:


ya have to look past storm surge in nola the pumps can't keep up with a surge and 20 inches of rain....


Article posted late last year on MSNBC

http://www.msnbc.msn.com/id/45066867/ns/us_news-l ife/t/six-years-after-katrina-slow-progress-nation s-levees/#.UDqGSaPALbw
Member Since: Posts: Comments:
1808. FOREX
Quoting sar2401:


No. I'll repeat...the entire northern Gulf coast remains in the cone. This won't even get close to a resolution in less than 24 hours.


Where I live in Panama City beach is not in the cone anymore, but maybe we should be.
Member Since: Posts: Comments:
1806. yoboi
Quoting GTcooliebai:
C'mon guys lets stop making comparisons to Katrina. It's more than enough for folks who went through the devastation to have to be reminded of it again. Just pray for the best.


it's better to not sugar coat things prepare for the worst hope for the best.....
Member Since: Posts: Comments:
Has anyone noticed plastic gas cans have more than doubled in price since Katrina? I think it was the 5 or 6 gal (whatever that larger one is) that was $17 and change at both Home Depot and Lowes. My gas cans have done better than any other investments.
Member Since: August 16, 2007 Posts: 0 Comments: 393
1803. timmoss
Quoting duranta:


I have lived in New Orleans for years. People were told to go to the superdome, but that it wasn't equipped for special needs. New Orleans had no evacuation plan that they were willing to enact. Buses were left in low ground. Many folks here live on little income as this city's "economy", if you want to call it that, is based on tourism and the service industry. Many couldn't afford to leave. Cuba has their act together when it comes to evacuation and shelter. Now New Orleans has a much better plan, with buses and shelter planned for as many that need it. It took much misery of thousands and deaths to get there. Shame.


I was going to say the same thing--I was In NOLA through the storm and the aftermath (sold my car the week before--that was a problem!). People were absolutely told to go to the Dome for shelter. Also, even with the "mandatory" evacuation, certain people were asked to stay--medical personnell and hotel workers--there were a LOT of tourists trapped in the city who couldn't get out.
Member Since: Posts: Comments:
1802. Caner
some fresh new convection starting to bubble up around the coc now.

Link
Member Since: Posts: Comments:
Quoting PalmBeachWeatherBoy:
Very strong rain band here in West Palm Beach, 50 mph gusts i would say, blinding rain, 3-4 rumbles of thunder. No damage in my neighborhood, but the flooding just doubled.


In Lake Worth. A few more like that and flooding will definitely be a widespread issue in PB County.
Member Since: Posts: Comments:
1800. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 33236
Hurricane hunter is a moment away from center pass. 995 mb so far. I'm guessing 992.2 mb.
Member Since: August 1, 2011 Posts: 23 Comments: 7449
Quoting MississippiWx:


C'mon just say it...

"Presslord and Angela, sittin' in a tree. K-i-s-s-i...."

LOL.
Member Since: Posts: Comments:
1797. yoboi
Quoting presslord:


using the words 'twit' and 'Bastardi' in the same sentence is redundant


press where is junkie at this eve???
Member Since: Posts: Comments:
Quoting 1900hurricane:
This blog is moving at ludicrous speed. Been a long time since I've seen it move this fast.
I posted a comment 2-min ago and it's already 3 pages back. By the way how fast is ludicrous anyway?
Member Since: Posts: Comments:
1795. sar2401
Quoting JGreco:


So is the Panhandle of Florida safe then...the Fort Walton Beach Destin area....specifically...


No. I'll repeat...the entire northern Gulf coast remains in the cone. This won't even get close to a resolution in less than 24 hours.
Member Since: Posts: Comments:
Quoting angelafritz:
I like the new music choices on TWC for Local On the 8s. 24 hour coverage of an approaching hurricane is very difficult, especially 3-5 days in advance of landfall, when the only changes we really see are from Hurricane Hunters and every three hours in the NHC advisories. Personally, I've enjoyed watching the TWC coverage of Isaac. I like seeing the conditions on the beaches where the reporters are located, and I like seeing the different ways that Bryan and his team explain current observations and forecasts to the viewers.

By the way, Doc is on around 4:30 EDT, so tune in! :)


TWC is always the best during an approaching storm. They usually have their A team around for prime time hours. Other than that.... :-/
Member Since: Posts: Comments:
we are still in the wall of the 'center' of Isaac. We are still experiencing heavy rains and strong winds. It's like we are in the 'creation' of the forming of eye over us. I mean that in the literal sense,,,back to movie and lots of food!
Member Since: Posts: Comments:
Quoting bappit:

Depends on where you are. Over the peninsula we are at Dmax.

FL peninsula?
Member Since: Posts: Comments:
Quoting katrinavet:
Katrina is nearly 7 years ago, guys. Can we leave it alone?


We learn from past mistakes. Houston did a "good" job evacuating for IKE after learning from the Rita cluster-eff. I am really hoping that N.O. doesn't get their solutions "tested" on Wednesday.
Member Since: Posts: Comments:
C'mon guys lets stop making comparisons to Katrina. It's more than enough for folks who went through the devastation to have to be reminded of it again. Just pray for the best.
Member Since: Posts: Comments:
1788. Levi32
Quoting TomTaylor:
Yeah but convection is rising air. If you have convection over a single consolidated and closed circulation pressures will fall, regardless of the MJO phase. My point is this didn't happen because of the broadness and the tradewinds preventing consolidation, not the sinking air of the leaving MJO.


No, no not true. Think about Ernesto. He looked like a near-hurricane on satellite with persistent deep -70C or lower convective tops for over 24 hours. The pressure rose during that time.
Member Since: Posts: Comments:
Looking at Isaac on doppler radar, it looks like it has slowed it's forward speed dramatically, the motion on radar appears uncertainly right now on radar.
Member Since: Posts: Comments:
Is it possible Isaac could still come inland near pensacola // mobile?? I see the euro model didnt budge takin Isaac into this area
Member Since: Posts: Comments:
Quoting aislinnpaps:


In the heat? Lili hit around 7 October and the weather was nice and cool. I also lost electric. That the weather was cool was the saving grace.


The opposite of Rita. That was hot.
Member Since: Posts: Comments:
Quoting presslord:
Angela is da house!!!!!! Now it's a party!!!!!


C'mon just say it...

"Presslord and Angela, sittin' in a tree. K-i-s-s-i...."
Member Since: Posts: Comments:
1783. angelafritz (Admin)
I like the new music choices on TWC for Local On the 8s. 24 hour coverage of an approaching hurricane is very difficult, especially 3-5 days in advance of landfall, when the only changes we really see are from Hurricane Hunters and every three hours in the NHC advisories. Personally, I've enjoyed watching the TWC coverage of Isaac. I like seeing the conditions on the beaches where the reporters are located, and I like seeing the different ways that Bryan and his team explain current observations and forecasts to the viewers.

By the way, Doc is on around 4:30 EDT, so tune in! :)
Quoting GeoffreyWPB:
Hopefully once this passes through West Palm, the worse will be over for southeast Fla.



Hopefully unless it works out that dry slot. Those discreet cells that are starting to form there are an indication of moistening.


Member Since: Posts: Comments:
Make you kind of appreciate hurricanes, at least we get some warning and can leave.
Quoting violet312s:
My goodness I would not want to be in Brawley, CA. The little quakes keep coming. That would freak me out.

Member Since: Posts: Comments:
1780. yoboi
Quoting MississippiWx:
Blog is moving so fast...posting this again here for emphasis:

Other than a bit of dry air initially, I'm not sure if Isaac could ask for better upper level conditions. He has an upper low backing away to his SW, another upper low to the SE of him, and an upper low along the Eastern Seaboard giving him excellent poleward outflow. Combine that with upper level ridging in the Gulf and the stage is set.



texas high is retreating...
Member Since: Posts: Comments:
1779. LargoFl
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT SUN AUG 26 2012

VALID 262000Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE FL
PENINSULA...

SEVERAL CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST
CHANGE IS TO REMOVE THE 10 PERCENT TORNADO PROBABILITY FROM SOUTH
FL. EXTENSIVE CLOUD COVER IS IN PLACE ACROSS SOUTH AND CNTRL FL WITH
THE ONLY EXCEPTION OVER SRN MIAMI-DADE COUNTY AND IN THE NERN FL
KEYS. SO FAR THE TENDENCY FOR STORMS TO ROTATE HAS BEEN LESS THAN
EXPECTED. ALTHOUGH A TORNADO THREAT WILL LIKELY CONTINUE THIS
AFTERNOON INTO THIS EVENING...THE THREAT MAY BE MORE ISOLATED THAN
WAS PREVIOUSLY THOUGHT. THE SECOND CHANGE TO THE OUTLOOK IS TO THE 5
PERCENT WIND AND 2 PERCENT TORNADO PROBABILITY CONTOURS IN THE
MID-ATLANTIC. THE ADJUSTMENT RE-ORIENTS THE CONTOURS FROM NORTH TO
SOUTH FROM SRN PA SWD INTO FAR SE VA WHICH LINES UP WITH THE BAND OF
FOCUSED CONVECTION AND AXIS OF MODERATE INSTABILITY. THE THIRD
CHANGE TO THE OUTLOOK IS TO ADD PARTS OF SE VA AND ERN SC INTO
THUNDER WHERE CONVECTION COULD MOVE INTO THE IMMEDIATE COASTAL
SECTIONS LATE IN THE PERIOD. THE FOURTH CHANGE IS TO ADD THUNDER
INTO THE RAPID CITY AREA WHERE AN ISOLATED THUNDERSTORM IS
DEVELOPING ATTM. OTHERWISE...A FEW MINOR TWEAKS HAVE BEEN MADE TO
THE THUNDER LINES IN OTHER AREAS OF THE US.

..BROYLES.. 08/26/2012
Member Since: August 6, 2011 Posts: 4 Comments: 33236
1778. GetReal
Quoting sar2401:


No, the entire northern Gulf coast is still in it. The models are battling on where Isaac is going, and some models are east and some are west. Just keep watching and, once the models begin to converge, we'll have a better idea who is at lower risk.



Time and distance is running out quickly, and decisions need to be made by officials relying upon the NHC.
Member Since: July 4, 2005 Posts: 204 Comments: 8802
1777. gator23
Quoting washingtonian115:
No.That storm has gone down in history for worst natural disaster.It affected the entire country one way or another.


And 20 years ago Andrew was the nation worst natural disaster and it sot Bush his presidency. It took until Katrina for people to move on from that.
Member Since: Posts: Comments:
Hello Everyone: According to the wunderground twitter account, New Orleans has declared a state of emergency.
Member Since: Posts: Comments:

Viewing: 1826 - 1776

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45Blog Index

Top of Page

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.