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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TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT WED AUG 29 2012

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
ISAAC...LOCATED ON THE COAST OF SOUTHEASTERN LOUISIANA AND ON
TROPICAL STORM KIRK...LOCATED ABOUT 1435 MILES SOUTHWEST OF THE
AZORES.

SHOWER AND THUNDERSTORM ACTIVITY HAS INCREASED A LITTLE IN
ASSOCIATION WITH A BROAD AREA OF LOW PRESSURE ALONG A TROPICAL WAVE
LOCATED ABOUT 700 MILES WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR GRADUAL
DEVELOPMENT DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...50 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT
ABOUT 15 MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
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hang on jason - if it keeps inching west along the coast it will be at vermilion bay a little later and lafayette will get "some" rain - (lafayette here too)
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1467. barbamz

Have to go. Stay safe with Isaac!
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Braithwaite is getting pounded and have water in people house up to 12 feet or more. This really sad on the anniversary of Katrina. I feel sorry for those people.
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1465. GetReal
Quoting Maineweatherguy20023:

Levee breach/failure in that area as well. on TWC Cantore was getting blasted on canal st



Those levees in that area are not all that high and are regularly topped by CAT 1 hurricanes.
Member Since: July 4, 2005 Posts: 204 Comments: 8806
1464. MahFL
Quoting CybrTeddy:
Current radar shows the eye is directly over Houma


It's not directly over Houma, Houma is in the NW side of the large eye, just a little way inside the eyewall.
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Plaquemines Parish levees overflowing and flooding area with 12 feet of water according to TWC. Possibly upto 60 people need rescued some on rooftops.
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Quoting LargoFl:
most of the traffic cams etc are down there, just tried


Chauvin LA live on stream here:
Link
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1461. Jax82
Its starting to add up already....

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Quoting GetReal:
The new and improved levees are having no problem handling Isaac tidal surge... Again the problem now is rain and leaves branches and general debris clogging drain grates ATT.



this is good and bad



the good new the new leaves are holding up for now



the bad new is people are going too put fath in them so my fearing is that will the new leves hold up with a cat 4 or 5 storm people may not want too leave town
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Quoting presslord:



yea...that was the last I heard, too...


Press have you heard anything new on Storm?
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A pretty naive (it seems) Fox8 Journalist tweeting that she is DRIVING in Houma, must be an area with lower winds due to the Eye. Good thing the storm is not on the move or she would be in danger from other side.

http://twitter.com/NewsCarolyn

See tv coverage from her and other local reporters here: http://www.fox8live.com/video
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Quoting biff4ugo:
Waves splashing on top of the 16' levee during a Cat 1 storm, when the levee was built for a Cat 3 storm, is NOT a confidence builder.
Isaac is looking fat on the east side and parked, so it is a long wet day ahead.
Don't most cell towers have backup generators? At least for a few hours? I realise that doesn't matter if the tower is blown down, but otherwise there should be some phone service.
I remember the land line days when the phone still worked even when the power was out.


the waves arent on the top of the nola levees etc are they?

I think a lot of people dodged a bullet with the mississippi river being 4 or more feet below normal..Imagine if it had been above normal or flooding.

Also isaac waited to the last second, if it had strengthened once before it could have piled up more water, or if it had closed its core just on one of the earlier chances it had it could have been much stronger too, if we should ever gappen to get a cat3 coming at this angle, it might be ballgame over, heck even another storm like isaac, that was stronger earlier and it would be a disaster, even at cat2...

Wonder if this is the last Isaac we will ever see
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Spoke briefly to Pat's wife...they're alive and hunkered down....Anybody want a puppy?!
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1455. LafLA
Quoting justsouthofnola:
Eye is currently over my house.... Not completely calm
Can I get a radar loop please. No power and phone radar loop only shows small amounts rain in the gom


It looks like based on Lafayette Radar the eye is over Houma and it is drifting west
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1454. Chiggy
Quoting AussieStorm:

Where was that report from. Fox 8 has only reported 80mph at Lake P


Sorry not sure but TWC says it was a legitimate....
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Quoting TropicalAnalystwx13:
Wonder what it looks like in Houma. Eye is passing directly overhead.


Just saw a live news report from inside the eye, not far from Houma. Calm winds, very little rain.

But that radar signature on Isaac looks thick and menacing.
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Quoting TropicalAnalystwx13:
So much for El Nino...waters are cooling.

aww man! what happened?
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Quoting Chiggy:
TWC just reported 110mph gusts... WOW

Where was that report from. Fox 8 has only reported 80mph at Lake P
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Quoting CybrTeddy:
Current radar shows the eye is directly over Houma


Looks like it's moving ever so slowly.
Member Since: August 24, 2010 Posts: 0 Comments: 682
Quoting AussieStorm:
Plaquemines Parish just successfully rescued 3 people from rooftop in Braithwaite. Residents & rescuers both safe! More to go though....

Levee breach/failure in that area as well. on TWC Cantore was getting blasted on canal st
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1448. LargoFl
Quoting TropicalAnalystwx13:
Wonder what it looks like in Houma. Eye is passing directly overhead.
most of the traffic cams etc are down there, just tried
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1447. Chiggy
TWC just reported 110mph gusts... WOW
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Mobile Live Video smack dab in the center of the eye near Chauvin LA. Power is still. Might not stay that when when the east eyewall comes in.
Link
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Quoting biff4ugo:
Waves splashing on top of the 16' levee during a Cat 1 storm, when the levee was built for a Cat 3 storm, is NOT a confidence builder.
Isaac is looking fat on the east side and parked, so it is a long wet day ahead.
Don't most cell towers have backup generators? At least for a few hours? I realise that doesn't matter if the tower is blown down, but otherwise there should be some phone service.
I remember the land line days when the phone still worked even when the power was out.


For all intents and purposes Isaac was a Category 3 when it comes to surge. This is why no one should underestimate hurricanes this large no matter the intensity (Irene, Ike)
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1444. GetReal
The new and improved levees are having no problem handling Isaac tidal surge... Again the problem now is rain and leaves branches and general debris clogging drain grates ATT.
Member Since: July 4, 2005 Posts: 204 Comments: 8806
1443. JasonRE
Where is the rain!!? In Lafayette LA here.....been getting gusts but not a drop!
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Heard that the storm surge overtopped the levees overnight, not good.
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Quoting CybrTeddy:
Current radar shows the eye is directly over Houma


And it doesn't look to be moving much.
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Quoting hydrus:
Just looked at the the New Orleans radar sequence..Just horrible...Storm has barely moved and S.E.LA, MS and AL-, all taking a prolonged beating.
Nightmare from HELL! GFS was very right when it said it was gonna move very slow
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Wonder what it looks like in Houma. Eye is passing directly overhead.
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Waves splashing on top of the 16' levee during a Cat 1 storm, when the levee was built for a Cat 3 storm, is NOT a confidence builder.
Isaac is looking fat on the east side and parked, so it is a long wet day ahead.
Don't most cell towers have backup generators? At least for a few hours? I realise that doesn't matter if the tower is blown down, but otherwise there should be some phone service.
I remember the land line days when the phone still worked even when the power was out.
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Current radar shows the eye is directly over Houma
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Quoting hydrus:
Just looked at the the New Orleans radar sequence..Just horrible...Storm has barely moved and S.E.LA, MS and AL-, all taking a prolonged beating.


Crikey...I shut down at 2am last, UK time. It's 1pm UK time now, and I wasn't expecting this image. Hardly moved at all AND looks to be stronger even, a big blow out of convection anyway.
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1435. LargoFl
Houma La radar........
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A cat 3 for 12-24 hours may not be equivelant to 24-48 hours of cat 1 that remains to be seen
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1433. barbamz
Daylight is coming in slowly. Vis sat.
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1432. GetReal
The problem that we are having now is the leaves clogging the drainage grates!!!
Member Since: July 4, 2005 Posts: 204 Comments: 8806
I'm concerned about drift along the coastline. How far will it go before it get picked up to go North?
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Quoting presslord:


www.stormjunkie.com

Thanks
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Eye is currently over my house.... Not completely calm
Can I get a radar loop please. No power and phone radar loop only shows small amounts rain in the gom
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Landreu said new Orleans. Levees aren't overtopping or busting, that's when u run
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1427. hydrus
Big wave and more on the way..A lot of moisture.
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So much for El Nino...waters are cooling.

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Quoting leftlink:
IR image confirms that the convection boom below the storm is over. Now there is a new convection boom, just south of Alabama. Formed 20 minutes ago. GEOS-14 image:


In Mobile. Got my dogs pottied in time.
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Quoting LargoFl:
yeah its pretty bad there..wish this storm would move but looks like it doesnt know where to go to..
like it said hold up wen i get to LA. smh this is crazy! heard reports saying by thursday night maybe some clearing
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1423. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
654 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* FLASH FLOOD WARNING FOR...
JEFFERSON PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...TIMBERLANE...METAIRIE...MARRERO...
KENNER...HARVEY...AVONDALE...
ORLEANS PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...NEW ORLEANS...EAST NEW ORLEANS...
CENTRAL ST. BERNARD PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF CHALMETTE...
ST. CHARLES PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF HAHNVILLE...

* UNTIL 945 AM CDT

* AT 650 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS CONTINUED
TO DETECT VERY HEAVY RAIN FROM THUNDERSTORMS OVER THE WARNED
AREA...AND REPORTS OF WIDESPREAD STREET FLOODING HAS BEEN RECEIVED
IN SOME AREAS.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
YSCLOSKEY...LAFITTE...JEAN LAFITTE AND BARATARIA
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Quoting GeorgiaStormz:


have you been outisde at all?


Ya there's two trees down to my north, and a flood to my west, I have one more Way out and will try and convince my parents.
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Quoting Masquer08er:
Now why did I think the comment about the media was political?



compassionate of her.
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1420. WxLogic
Good Morning
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1419. vince1
Fox 8 died, suddenly.

EDIT: Only temporary.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.