Hurricane Isaac hits Louisiana, driving dangerous storm surges

By: Dr. Jeff Masters , 2:27 AM GMT on August 29, 2012

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Hurricane Isaac is ashore over Southeast Louisiana, having officially crossed the coast on the Mississippi Delta 90 miles southeast of New Orleans at 7:45 am EDT on August 28. Isaac intensified right up until landfall, striking with 80 mph winds and a central pressure of 970 mb. The storm's large size and large 50 - 60 mile diameter eye kept the intensification rate slow today, but it came quite close to becoming a significantly more dangerous storm. That's because at landfall, Isaac was in the midst of establishing a small inner eyewall within its large 50-mile diameter eye, a very rare feat I've never seen before. Usually, when an eye first forms, it gradually contracts, eventually becoming so small that it becomes unstable. An outer concentric eyewall then forms around the small inner eyewall, eventually becoming the only eyewall when the inner eyewall collapses. But Isaac is a very unusual storm that has continually surprised us, and this inside-out concentric eyewall formation fits the storm's unusual character. The storm isn't in a hurry to move fully inland, and has slowed down to a crawl this evening. This will give the storm the opportunity to keep its center mostly over water a few more hours, and maintain hurricane strength into the early morning on Wednesday.


Figure 1. Radar reflectivity image from New Orleans as Isaac made landfall at 6 pm CDT August 28, 2012.

A dangerous storm surge event underway
Isaac is bringing large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. At 10 pm EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

6.2' Waveland, MS
9.9' Shell Beach, LA
3.0' Pensacola, FL
4.4' Pascagoula, MS
3.4' Mobile, AL

The 9.9' storm surge at Shell Beach, which is in Lake Borgne 20 miles southeast of New Orleans, exceeds the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. Research scientists running a Doppler on Wheels radar located on top of the 16' levees in Plaquemines Parish near Port Sulphur, LA, reported at 8:30 pm EDT that a storm surge of 14' moved up the Mississippi River, and was just 2' below the levees. Waves on top of the surge were cresting over the west side of the levee. Needless to say, they were very nervous. Over the past hour, the surge has retreated some, and waves were no longer lapping over the top of the levee. This is probably due to the fact that we're headed towards low tide. A storm surge of 9.5' has moved up the Mississippi River to the Carrrollton gauge in New Orleans. This is not a concern for the levees in New Orleans, since the storm surge has now brought the river up to 2.5' above its normal water level, which was 7' low due to the 2012 U.S. drought. The highest rise of the water above ground level will occur Wednesday morning over much of Southeast Louisiana, Mississippi, Alabama, and the western Florida Panhandle, when the tide comes back in. It is clear now that this storm surge event will be as dangerous as that of Category 2 Hurricane Gustav of 2008. One piece of good news: NWS New Orleans successfully launched their 00Z balloon. However, their discussion noted the atmosphere is "saturated or nearly saturated" all the way up to 470mb, or 20,000 feet. Precipitable water was 2.76 inches, which will be ripe for extremely heavy rainfall.


Figure 2. Tide gauge data from Shell Beach, located on the south shore of Lake Borgne, just east of New Orleans. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.)

Portlight disaster relief charity responds to Issac
The Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, have mobilized resources in advance of the arrival of Hurricane Isaac. Their crew, including 2 EMTs, is at the Biloxi Special Needs Shelter, and will be caring for shelter dwellers and doing rescues of people who call for help. Another team will be surveying all the shelters in the area to ensure that they are accessible to all people. You can donate to Portlight's disaster relief fund here.

I'll have more in the morning. Hunker down, New Orleans. It's going to be a long night.

Jeff Masters

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looks like dry air may be trying to work its way into the center as well. imo
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55 mph here on the northshore mandeville
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fudge, TWC just making case for it moving west along coast toward TEJAS.....
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Quoting louisianaboy444:
Is it just me or is the center wobbling WSW?
What part of Louisiana are you located?
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Quoting GeauxGirl:


Wow. Was just there for vacay. Wonder if the Flor-Bama is rockin'? ;-)


Love that place! The lower level of the FB is probably under water right now :(
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Quoting MercForHire:


That's what I've been watching for 10 minutes & I THINK I figured it out. That building straight across the intersection is a bar & they are having a hurricane party. Somebody inside got too drunk & caused a scene.

Those cops & soldiers showed up REALLY quick & at same time, so it was some type of dispatch call.
he first tried to tract Ernesto, then tried to forecast isaacs strength. can ya blame him for drinking?
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Is it me, or does the eye look like it's beginning to contract in the last couple radar frames?
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Interesting. RT @StuOstro: The change in symmetry in the past 24 hours http://t.co/x34Z02NP #Isaac -- Weather Underground (@wunderground)
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Will be interesting to see next pressure reading on next pass. Looks better than last time it made a pass.
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TWC working in my part of LA no problem...

Los Angeles that is.
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Latest infrared:

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I am thinking that the next jog may be either due south or south east...

Almost looks like it wants to do a loop.
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Crews clock 110 mph winds in Myrtle Grove. Lots of high voltage powering lines on LA 23 & drooping across it near energy sub station. #Isaac
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Quoting runnomore:


I hate that side of town to much traffic.
It will be interesting to see what he does over the next few hrs. Guess I need to get some sleep have to be up In 4 hrs for work.


Yeah buddy get some rest. I should get some too..just in case Isaac decides to pay us a little visit. Have a good one.
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Quoting BrazoriaMan:


Good man. I honestly did not think anything would happen here..and it very well still might not, so have not stocked up on anything. I wonder what the am will bring.


good thing is that you can always use it later.
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Is it just me or is the center wobbling WSW?
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He's straight-up stuck right now.

Seriously, I don't see where he goes until some stuff shifts or that ridge breaks. Westish, I guess, but he's got increasing reasons to be leery of it.
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Just curious why the satellite presentation of circulation is east of the radar presentation? (Utilizing the highly scientific pencil on the screen method).

Have I been staring at the pretty colors too long?
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Will there be model runs on Isaac tonight? I am anxious to see what they have to show and if they are all in agreement.
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Quoting tennisgirl08:
Buoy 42012 was reporting wave heights of near 20 ft.
Near Orange Beach, Alabama.


Not surprising after those pier images were posted earlier on the blog.

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598. Skyepony (Mod)
Just saw the power blow in Houma & then it came back on, on chaser cam..
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597. BtnTx
Quoting Orcasystems:


It was a day early... it appears to be waiting for the anniversary date :(
Good to see you are still around Orca
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Maybe Isaac doesn't like Cajun food? :P
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Quoting SomeRandomTexan:
I went to Wal-Mart tonight to get some water and batteries. They had a big stack of waters by the front door. I think we were the only ones buying any. Figured best have and and not need it than be wishing for it later.


Good man. I honestly did not think anything would happen here..and it very well still might not, so have not stocked up on anything. I wonder what the am will bring.
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Quoting AllyBama:


WOW! it s storming at your house? it is mine!


Yes, bad. Worst conditions as of yet.
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Isaac is tracing the coastline for a bit

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Quoting tennisgirl08:
Buoy 42012 was reporting wave heights of near 20 ft.
Near Orange Beach, Alabama.


Wow. Was just there for vacay. Wonder if the Flor-Bama is rockin'? ;-)
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Quoting TampaFLUSA:
Local Fox Station in New Orleans streaming

Link


THANKS!!
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Heavy rain and gusty winds in Mobile now. These NE feeder bands aren't playing around anymore.
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Quoting BrazoriaMan:


Good eveing fellow Pearlanders. Wal Mart run anyone? We may need it! Dixie Farm one tho! Silverlake is tooo busy!


The one on main is pretty busy too...still a mad rush for school supplies
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Quoting traumaboyy:


Morning AtHome!!

Glad to be sitting this one out!! Two days ago they had it running over my house....At least gave us the chance to knock the dirt dobblers out of the generators and I got three hundred gallons of water ready to go.....all we got wuz beautiful weather and a break from the rain!! Besides the skeeters...how are things in Texas??


Pretty nice today. North breeze knocked the humidity down some. Looks like I'll be watching this one from the side lines as well. :)
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Writing a blog on Isaac, tough since reports keep coming in and him always changing. I'll try to get it out in a bit.
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West jogs have southern component and happening more frequent. Causing path to be west. Wait and see if next N jog less than S jog. I think that would confirm track change.
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Quoting MercForHire:


That's what I've been watching for 10 minutes & I THINK I figured it out. That building straight across the intersection is a bar & they are having a hurricane party. Somebody inside got too drunk & caused a scene.

Those cops & soldiers showed up REALLY quick & at same time, so it was some type of dispatch call.


Thanks... Came back to check it out and found that scene...
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Quoting tennisgirl08:
Buoy 42012 was reporting wave heights of near 20 ft.
Near Orange Beach, Alabama.


WOW! it s storming at your house? it is mine!
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Quoting BrazoriaMan:


Good eveing fellow Pearlanders. Wal Mart run anyone? We may need it! Dixie Farm one tho! Silverlake is tooo busy!


I hate that side of town to much traffic.
It will be interesting to see what he does over the next few hrs. Guess I need to get some sleep have to be up In 4 hrs for work.
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Quoting GTcooliebai:
Agree, I used to think winds were the biggest issues in a hurricane, not anymore, especially after I went through Debby and she was a Tropical Storm. Rain and Surge seems to be the biggest issue with this storm.

When I was younger I thought that. After seeing storms like this water is a major issue with wind a threat as well.
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Quoting xtremeweathertracker:
NATIONAL WEATHER SERVICE LAKE CHARLES LA
1109 PM CDT TUE AUG 28 2012

.DISCUSSION...
THE 1030 PM RADAR MOSAIC DEPICTS THE EYE OF HURRICANE ISAAC
SITUATED JUST SOUTH OF PORT FOURCHON. WITH A CONTINUED WESTWARD JOG.



How many continued jogs before they consider it a track change...lol
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Quoting KEEPEROFTHEGATE:


Grand Isle getting it bad right now.
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Quoting sunlinepr:
Check the Bourbon Cam.... small crowd and a police car.... there...

Link


That's what I've been watching for 10 minutes & I THINK I figured it out. That building straight across the intersection is a bar & they are having a hurricane party. Somebody inside got too drunk & caused a scene.

Those cops & soldiers showed up REALLY quick & at same time, so it was some type of dispatch call.
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Last post for the night. Prayers to those being affected by Isaac tonight, stay safe. Isaac almost complete with the solid ring of deep convection around the center. Don't be surprised to see winds increase overnight.

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NATIONAL WEATHER SERVICE LAKE CHARLES LA
1109 PM CDT TUE AUG 28 2012

.DISCUSSION...
THE 1030 PM RADAR MOSAIC DEPICTS THE EYE OF HURRICANE ISAAC
SITUATED JUST SOUTH OF PORT FOURCHON. WITH A CONTINUED WESTWARD JOG.

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Not going to be making 2nd landfall at Grand Isle like perdicted.
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TWC just went live in Central Florida after a minute of breaking up coverage.

Odd Storm, brushed the shore and then headed west off the shore.
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Latest storm surge levels: Shell Beach LA 11.0 ft; Waveland MS 6.9 ft; Dauphin Island AL 3.5 ft; Pensacola FL 3.0 ft. #Isaac
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Quoting Ryuujin:


it's the idea and the care for a human life. Not the act.


I understand, but calling 911 is an act. I was merely explaining that there are many questions that can't ba answered if you did call 911, and they won't be responding to anything but dire emergencies. Just the way things go when the stuff hits the fan.
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Quoting wxchaser97:

Niether do I, even though Isaac is "only a cat1" he is still dangerous.
Agree, I used to think winds were the biggest issues in a hurricane, not anymore, especially after I went through Debby and she was a Tropical Storm. Rain and Surge seems to be the biggest issue with this storm. And wind gust in these spiral bands, probably producing fast spin-ups.
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Quoting SomeRandomTexan:
the eye has perfect symmetry in that last frame.
and if it gets past that last southern tip? tx?
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Quoting AussieStorm:

Are you able to give me a link to TWC?



here Link
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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.