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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Member Since: Posts: Comments:
1625. Levi32
Quoting TomTaylor:
Not sure about the large scale sinking in the western Caribbean preventing the storm from being vertically stacked. We often see large areas of sinking air behind or even in front of an intensifying storm (ULL retrograding to the SW). The fact remains that a large amount of convection (upward motion) was present over Isaac while he was in the eastern and central Caribbean. The environmental problems I see are a broad circulation failing to consolidate due to fast trade winds. This kept storm motion fast, preventing significant consolidation, and additionally, the maintenance of strong trade winds ahead of the storm further prevented consolidation. As a result, we saw multiple vorticies swirl around each other at times and numerous center relocations. Dry air intrusion was also an issue and sinking air ahead of the storm isn't helpful, but the root of the issue (issue being the failure to become vertically stacked and consolidate under over LLC) seems to be the broad size and fast trade winds flow.


I said the trade winds and broadness were two of the problems.

The large-scale sinking is a clear problem. We saw with Ernesto how convection can go off very deeply but the pressures don't fall. The only way that can happen is if sinking air is offsetting the rising air causing the thunderstorms. With accelerating trade winds ahead of the storm and the MJO switching phases out ahead of it, the Caribbean was favored for sinking air, not for pressure falls.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Sorry I had to bring up K...
Member Since: August 14, 2010 Posts: 10 Comments: 16400
Quoting AtHomeInTX:


Quite a cone.


I noticed that too. At least 600 miles? On the N Gulf coat.
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Quoting Bluestorm5:
You Floridians were yelling at us earlier that it wasn't a serious storm. Jesus.


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
Member Since: August 18, 2008 Posts: 0 Comments: 467
"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
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Quoting GTcooliebai:
That's the NAVY cone different from the NHC, but it also shows the range of the TS force winds.


Oh ok.
Member Since: August 24, 2010 Posts: 0 Comments: 676
3 storms had the name isaac. Isaacs storm, the 1900 hurricane in galvaston, hurricane ike (ike is a nickname of isaac), and the current TS. The first 2 isaacs hit galvaston, the models are pushing this isaac further west every run. I never thought it would go this far, but i am beginning to wonder....

Also, the first 2 isaacs pushed very strong winds far inland.
Member Since: Posts: Comments:
When is the next recon?
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Quoting WetBankGuy:
As of now, NOLA is saying prepare to shelter in place until more information on path is available.


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...
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Quoting Caladesian:
Another member posted some good disaster preparation tips. Here is one more for any newbies who might be affected by power outages from this storm:
fill all your extra containers (empty milk jugs, water bottles, etc.) and place them in the freezer until it is packed. A packed freezer stays colder than one with lots of empty space. Any time you take something from the freezer, fill the space with another water container.

The extra ice will help keep things cold and may save your frozen goods if you only lose power for a short time. If you do lose power for a long time, at least you have another source of drinking water.
Not healthy to drink water from a once filled with milk jug.
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@reedtimmerTVN

Surface pressure of 997 mb measured at Key West, FL in Tropical Storm #Isaac!
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1614. Grothar
Quoting hurricanehanna:

dang Gro...just not likin' this one bit.



Large storm! I don't like hype, but I am concerned with this one.
Member Since: July 17, 2009 Posts: 69 Comments: 25326
Member Since: Posts: Comments:
Quoting breeezee:

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


I hope you are not calling the people who were left without shelter MORONS...who are you calling "those morons" ?
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CNN report on Bolaven, reporting wind gusts up to 161 mph:

http://www.cnn.com/2012/08/26/world/asia/typhoon- bolaven/index.html?hpt=hp_t1

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Quoting newportrinative:


I have cabin fever in Oakland Park, FL. It's so bad that I'm almost excited about going to work tomorrow.


We just started getting our first claps of thunder of the day here in West Boynton too. Also some heavy rain along with it but it has tappered off again
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Quoting breeezee:
tomorrow is going to be a very busy monday from nawlins to talahaseeeee
where did you here that
Quoting yoboi:


alot of people have no way to evac unless gov helps them.....you can bash them if ya like but it's a reality...
Quoting muddertracker:


There HAS to be shelters in a major city...that is just plain crazy. What about seniors and non-drivers? Please!


Just what Ive been hearing off the Weather channel.
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Quoting CosmicEvents:
I've been keeping track of the ants and compiling the reports since those days, via postings here and private messages. The ants, fwiw, are indicating more Texas coast over any other spot on the Gulf Coast.


Interesting - thanks for the update. Maybe I should copy and paste for the Pyrate Queen. :)
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.
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Quoting LADobeLady:
Yeah but you can park  your car on the neutral ground LOL  Save the cars!



Well...IF worse comes to worse...at least they won't be spending millions of dollars to fix it (Superdome) again...maybe this time they'll spend the money helping citizens in need. (Although I can't say much...our own fine Texas govenor spent money rebuilding his mansion instead of helping out those affected by Ike)
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Quoting TreasureCoastFl:
I truly hope people in evacuation area's do evacuate rather than attempt to ride it out. I truly hope they learned from K.


They are saying prepare to shelter in place until evacuation is ordered.
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1603. HrDelta
Quoting gator23:


Homeowners insurance in Florida wasnt available. The state had to create a state funded one


Speaking of Home Insurance, the stuff after Katrina convinced me insurance companies are evil.
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Quoting gator23:


I see so when it was near Florida you didnt care. This blog has a gulf bias. Millions of people where in harms way but it just NOW got serious?
You Floridians were yelling at us earlier that it wasn't a serious storm. Jesus.
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Yes and bring them to shelters in the north part of the state and I think surrounding states if needed.  
Quoting TreasureCoastFl:
If its a mandatory evacuation would they supply busses or something?

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1600. airmet3
Quoting bluebonnetgirl:
Just curious, what are some of the models seeing that would bring this storm to the west???? Our local news here in SETX said yesterday that we have a high over Texas that would protect us from Isaac. Is the high moving??


The high is building in from the west. It looks like a model or two do not think this high will be strong enough by the middle of the week to counteract the high also building from the east.
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Quoting yoboi:
shelter in place for nola too late if they even wanted to evac...hope isaac does not get strong...


If it comes our direction we'll probably have to do the same.
Member Since: August 24, 2010 Posts: 0 Comments: 676
1598. robj144
Quoting KeyWestbeachcomber:

You can see it because you are the private party


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.
Member Since: Posts: Comments:
Another member posted some good disaster preparation tips. Here is one more for any newbies who might be affected by power outages from this storm:
fill all your extra containers (empty milk jugs, water bottles, etc.) and place them in the freezer until it is packed. A packed freezer stays colder than one with lots of empty space. Any time you take something from the freezer, fill the space with another water container.

The extra ice will help keep things cold and may save your frozen goods if you only lose power for a short time. If you do lose power for a long time, at least you have another source of drinking water.
Member Since: Posts: Comments:
Corps of Engineers: There will be time to close all of the surge protection gates ahead of Isaac
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Storm surge is going to likely be a huge issue.Depending on where he makes landfall(and how strong) anywhere from 15-23ft is possible.
Member Since: August 14, 2010 Posts: 10 Comments: 16400
Quoting sar2401:


Say what? Where did you hear hurricane warnings are being issued for such a large area?

I mean. That The region will VERY likely receive Hurricane warnings at the 5pm Advisory...
Most likely Baton Rouge to Mobile.
Member Since: Posts: Comments:
1593. gator23
Quoting Bluestorm5:
Now the fun of the tracking became serious now.


I see so when it was near Florida you didnt care. This blog has a gulf bias. Millions of people where in harms way but it just NOW got serious?
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Quoting muddertracker:


There HAS to be shelters in a major city...that is just plain crazy. What about seniors and non-drivers? Please!
did you see what those morons did to the superdome during katrina
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Quoting muddertracker:


There HAS to be shelters in a major city...that is just plain crazy. What about seniors and non-drivers? Please!
If its a mandatory evacuation would they supply busses or something?
Member Since: August 18, 2008 Posts: 0 Comments: 467
Lee County, FL Emergency Management
FYI: At the direction of the Florida State Emergency Operations Center, immediately, tolls will be suspended eastbound, only, on the portion of I-75 in Collier County known as Alligator Alley to aid in evacuation efforts.
posted on FB
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Strongest rain band of the day just came through west palm beach. I heard thunder 3 times so far, plenty of wind and rain.
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1588. yoboi
Quoting HurricaneDean07:

Mayor of New Orleans said Superdome and other large buildings are not going to be used as shelters... This system is very unpredictable, and if Mandatory Evacuations are ordered. HEED THEM, there will not be any shelters in the case Evacuations are ordered.

Hurricane Warnings being issued from Baton Rouge to Pensacola going into affect at the 5pm Advisory.


alot of people have no way to evac unless gov helps them.....you can bash them if ya like but it's a reality...
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Quoting sar2401:


This is your fifth post and you're predicting a monster cat 3 to hit NOLA, based on some kind of prediction you made for Europe last year? If you're not a troll, you might want to not use terms like "monster" when there's absolutely no evidence to support such a claim.


I am not here to argue with somebody. It is my opinion. Sorry if i offended you with my forecast.
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1586. robj144
I guess it was because it's still private. Changed it:

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Quoting AtHomeInTX:


Quite a cone.
That's the NAVY cone different from the NHC, but it also shows the range of the TS force winds.
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Quoting KeyWestbeachcomber:

You can see it because you are the private party


It said private to me too. Could not see it.
Member Since: August 18, 2008 Posts: 0 Comments: 467
Quoting CoopsWife:
1443


Oh, Lordy - I remember way back when LaDobe Lady had ant issues - just before the storm we will not name. Have been wondering when/if someone would post what's going on in the animal/insect world.
I've been keeping track of the ants and compiling the reports since those days, via postings here and private messages. The ants, fwiw, are indicating more Texas coast over any other spot on the Gulf Coast.
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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.
34 hours the Mayor said.
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Quoting robj144:


I see it here. No one else sees it?

You can see it because you are the private party
Member Since: Posts: Comments:
1580. ITCZ
Quoting sar2401:


I'd say WHEW along about Wednesday. :)




LOL True, true. :) I lost my husband this time last year--I'm a little nervous without him.
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Yeah but you can park  your car on the neutral ground LOL  Save the cars!
Quoting Bluestorm5:
Mayor Landrieu: In the event an evacuation is called, everybody needs to make preparations. Superdome will not be shelters of last resort

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Quoting HurricaneDean07:

Mayor of New Orleans said Superdome and other large buildings are not going to be used as shelters... This system is very unpredictable, and if Mandatory Evacuations are ordered. HEED THEM, there will not be any shelters in the case Evacuations are ordered.

Hurricane Warnings being issued from Baton Rouge to Pensacola going into affect at the 5pm Advisory.


There HAS to be shelters in a major city...that is just plain crazy. What about seniors and non-drivers? Please!
Member Since: Posts: Comments:
Quoting HurricaneDean07:

Mayor of New Orleans said Superdome and other large buildings are not going to be used as shelters... This system is very unpredictable, and if Mandatory Evacuations are ordered. HEED THEM, there will not be any shelters in the case Evacuations are ordered.

Hurricane Warnings being issued from Baton Rouge to Pensacola going into affect at the 5pm Advisory.
I truly hope people in evacuation area's do evacuate rather than attempt to ride it out. I truly hope they learned from K.
Member Since: August 18, 2008 Posts: 0 Comments: 467
1576. sar2401
Quoting HurricaneDean07:

Mayor of New Orleans said Superdome and other large buildings are not going to be used as shelters... This system is very unpredictable, and if Mandatory Evacuations are ordered. HEED THEM, there will not be any shelters in the case Evacuations are ordered.

Hurricane Warnings being issued from Baton Rouge to Pensacola going into affect at the 5pm Advisory.


Say what? Where did you hear hurricane warnings are being issued for such a large area?
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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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