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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Quoting AtHomeInTX:


Was this on Facebook?

No its on the KFDM site
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Quoting Bobsled27:


Actually, the Superdome was never intended as a shelter. In fact, people were told NOT to go there because there were no resources and it wasn't safe. But they came anyway, and you saw the results.

Before you start judging what those scattered,shattered frightened people did..Float a mile in their coolers..Then tell me how you feel.
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Becoming better organized.
Link

Still dry air on the west side of the developing CDO, but it is looking much more impressive than this AM.
Member Since: July 8, 2005 Posts: 259 Comments: 23627
1673. angelafritz (Admin)
Quoting sar2401:


I think you're absolutely wrong. There isn't even a hurricane to warn about yet. The NHC doesn't jump the gun like that.


We're expected a hurricane warning for the northern Gulf in the 5pm. A hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.
Quoting robj144:


Not on my screen it isn't:



It should work.
It worked for me now
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Quoting LADobeLady:
Yes and bring them to shelters in the north part of the state and I think surrounding states if needed.  



I just want to debunk an old Katrina myth before it's starts getting legs. There are not enough buses in the NOLA area to evacuate the number of people who do not have cars.

That 400 bus figure was high and pre-Katrina. RTA runs 32 lines, many only two buses at a time.

http://wetbankguide.blogspot.com/search?q=buses
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Is there still a possibility Isaac could still make landfall in Fla. panhandle????
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When the levees where re-built, after Katrina, what were they built to withstand? Also, did they install a better pumping system, to withstand a Katrina strength storm? Anyone know? I hope they planned for a worse case situation. . . and hope they don't have to hope it works.
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Quoting AtHomeInTX:


Crap! Sorry I'm running out of nicer words.

Gets your attention fast!
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Quoting Stormchaser121:
"Some computer models then take Isaac more westerly with some risk that the storm could move into East Texas Friday. Obviously, a more westerly track will bring us much more of an impact Thursday and Friday with gusty winds and locally heavy rains. By the way, there is the chance that Isaac could become a CAT2 or CAT3 at landfall Wednesday night." -KFDM 6


Was this on Facebook?
Member Since: August 24, 2010 Posts: 0 Comments: 682
1665. yoboi
what are peoples thought with the 5?? west, east or same cone???
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1664. BrandiQ
I have a question... is the storm already done in south Florida or is it just getting started?
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1663. pottery
Quoting muddertracker:


Thank you. I was not sure how to respond to that without getting banned.

It was a bit of a challenge......
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1661. ITCZ
Quoting robj144:


Not on my screen it isn't:



It should work.


it worked for me too.
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Quoting pottery:

As far as I recall, those "morons" were herded in there, with no thought about how they were going to eat, cook, sleep, crap, or anything else....

It was a disaster, due to complete lack of planning by anyone....


Not exactly...many of them drove to the Dome and parked their cars and lined up on Saturday. Yes, I was there. I was also there 2 days after the storm in a Coast Guard chopper seeing people rescued from roof tops and emergency medical from the Dome
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View of the currently active NHC forecast. Green pins map the outside of the 2/3rd's cone.

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let's not be cute here folks....'moron' is code for an ugly racial epithet....
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Quoting RTSplayer:


It's already too late to evacuate for the HWRF Cat 4 scenario anyway. It's too strong and moving too fast.


Euro and GFDL are not too much weaker, 10 to 20mb, like a category...


Almost; if folks want to leave in the effected area's tonight and in the morning before noon is the time after that might be to late
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if i re call Hurricane Katrina made land fall in Buras-Triumph, Louisiana what are mode runs showing for land fall with are I storm in the same spot?
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Quoting gator23:


TCFL is right, I am sorry Blue
It's fine...
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1653. GetReal
Member Since: July 4, 2005 Posts: 204 Comments: 8806
Quoting FOREX:


I wonder if the gfs can predict quakes?? lol


Feeling em in San Diego...rolling rolling rolling. Hope it slows down cause dat just ain't right.
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Quoting pottery:

As far as I recall, those "morons" were herded in there, with no thought about how they were going to eat, cook, sleep, crap, or anything else....

It was a disaster, due to complete lack of planning by anyone....


Actually, the Superdome was never intended as a shelter. In fact, people were told NOT to go there because there were no resources and it wasn't safe. But they came anyway, and you saw the results.
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1650. robj144
Let's do this one more time. I know it's set to public now:

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1649. gator23
Quoting TreasureCoastFl:


Come on people, its not a competition. One death from a storm is one too many in any area. Haiti has already had deaths. Prayers to all of you that will be effected from this storm. If you are told to evacuate, please do so. Right now it looks like the entire gulf coast should be very watchful and preparing


TCFL is right, I am sorry Blue
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1648. GetReal
Member Since: July 4, 2005 Posts: 204 Comments: 8806
Quoting CosmicEvents:
Good point.....but realistically, if it wasn't for Cuba and Hispaniola Florida would likely be as desolate as the Baja Peninsula. Place never would have had much of a population.


well thats because baja is basically desert and its in mexico which means they dont have the resources to sustain desert life like in the sw usa, florida is very lush, but yeah destruction all around the state would be worse if no for the greater antillies all around therefore making less people want to live there, but i still think it would be a very populous state..i mean look at all the countries around the world that are in harms way of tropical cyclones. people love that warm water. im one of them
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1646. airmet3
Quoting HurricaneDean07:

I mean. That The region will VERY likely receive Hurricane warnings at the 5pm Advisory...
Most likely Baton Rouge to Mobile.


Thanks for the clarification. In the whole scheme of things, that is not alot of coastline this far out.
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1645. sar2401
Quoting HurricaneDean07:

I mean. That The region will VERY likely receive Hurricane warnings at the 5pm Advisory...
Most likely Baton Rouge to Mobile.


I think you're absolutely wrong. There isn't even a hurricane to warn about yet. The NHC doesn't jump the gun like that.
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Quoting dmh1026:
Wind picked up, and so did the rain...eased off now...it seems to be coming in waves...no lightning or thunder.


Thanks,keep the updates coming :)
Member Since: September 18, 2010 Posts: 0 Comments: 5156
1643. FOREX
Quoting SubtropicalHi:
4.5 Earthquake: Westmorland, CA (12 minutes ago) 4.1 Earthquake: Brawley, CA (13 minutes ago) 4.9 Earthquake: Brawley, CA (19 minutes ago) 5.3 Earthquake: Brawley, CA (21 minutes ago) 5.3 Earthquake: Brawley, CA (21 minutes ago) 4.7 Earthquake: Brawley, CA (31 minutes ago) 4.6 Earthquake: Brawley, CA (32 minutes ago) 4.0 Earthquake: Brawley, CA (35 minutes ago) 4.0 Earthquake: Brawley, CA (36 minutes ago)


I wonder if the gfs can predict quakes?? lol
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1642. GetReal
/
Member Since: July 4, 2005 Posts: 204 Comments: 8806
Quoting RTSplayer:
Oh my...

At present speed the storm can reach NOLA so fast...

I think just under 40 hours from the current center fix.


Isaac is predicted to slow down in the Gulf, so around 72hrs.
Member Since: July 8, 2005 Posts: 259 Comments: 23627
1639. robj144
Quoting violet312s:


It's still set to private.


Not on my screen it isn't:



It should work.
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Quoting robj144:


Right, but I hit the share link. You can share private videos with others and the video is still not "public". I've done it many times on facebook. Don't know the logistics here though. I changed it to public anyhow.

I would like to see it If you would be kind and repost the link thanks
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Quoting Stormchaser121:
"Some computer models then take Isaac more westerly with some risk that the storm could move into East Texas Friday. Obviously, a more westerly track will bring us much more of an impact Thursday and Friday with gusty winds and locally heavy rains. By the way, there is the chance that Isaac could become a CAT2 or CAT3 at landfall Wednesday night." -KFDM 6


Crap! Sorry I'm running out of nicer words.
Member Since: August 24, 2010 Posts: 0 Comments: 682
Quoting WxGeekVA:
Basically, if you are in New Orleans, or you have family in New Orleans, you might want to leave or tell them to leave now before feces hit the rotating oscillator. This could potentially be a KATRINA SIZE disaster, and people need to be aware of this now and leave while they still have a chance.

Please follow instructions of local officials though, as I am not an official source of imformation. It is just my opinion that this could be very bad, and that I want to try to help people avoid loss of life or property.


Hmmmm....Alarmist much?
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Quoting pottery:

As far as I recall, those "morons" were herded in there, with no thought about how they were going to eat, cook, sleep, crap, or anything else....

It was a disaster, due to complete lack of planning by anyone....


Thank you. I was not sure how to respond to that without getting banned.
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1634. Grothar
Quoting LightningCharmer:
Just sat here and typed it while listing to Isaac's winds. It was not copied and pasted. It would have been something I would have posted last year as well regarding this subject. Guess I'm consistent.


Yes, very consistent. Thanks for answering.
Member Since: July 17, 2009 Posts: 69 Comments: 25467
Isaac is jogging north, just look at him
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Current DOOM:CON level
Member Since: September 3, 2011 Posts: 13 Comments: 3468
Quoting TreasureCoastFl:
If its a mandatory evacuation would they supply busses or something?


Not sure..perhaps an LA native would know?
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Basically, if you are in New Orleans, or you have family in New Orleans, you might want to leave or tell them to leave now before feces hit the rotating oscillator. This could potentially be a KATRINA SIZE disaster, and people need to be aware of this now and leave while they still have a chance.

Please follow instructions of local officials though, as I am not an official source of imformation. It is just my opinion that this could be very bad, and that I want to try to help people avoid loss of life or property.
Member Since: September 3, 2011 Posts: 13 Comments: 3468
1629. ncstorm
For all those in the path of Isaac, please be safe and heed all warnings..NC got your back..
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1628. pottery
Quoting breeezee:

did you see what those morons did to the superdome during katrina

As far as I recall, those "morons" were herded in there, with no thought about how they were going to eat, cook, sleep, crap, or anything else....

It was a disaster, due to complete lack of planning by anyone....
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Quoting Jwd41190:
When is the next recon?
Right now, it's about to enter the storm again for 4th pass
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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.