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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Quoting geecheegirl:


Cannot feel sorry..they were told to evacuate.
Cyborgs don't feel pain.
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Quoting LargoFl:
geez this is bad, where are those people who said..oh..its just a tropical storm huh..news reports are bad in many area's over there..at least you still have power
Yeah but our garage is starting to fill up with water somewhat but its the wind that is tearing things up out here. House collapse in mid city, fire broke out in Gretna and chalmette and power is out to 475,000 people and heard it could take up to 4-5 days before getting power back
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Quoting GetReal:
I'll be back posting in and out over the next few hours... Currently we are experiencing the heaviest rains so far associated with Isaac... Reports of widespread street flooding starting to come in. The winds have remained a constant 45 to 60 mph with gust up to 80 mph....

I am observing some minor roof damage, and siding coming coming peeling off the side of homes. Easily 70% of the NOLA area is out of power now...


Actually it's about 50% judging by the latest numbers
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Quoting AtHomeInTX:
Morning Wes, Charliesgirl, 98, all. Some harrowing tales out there. Stay safe over there. And I hope Isaac gets a move on quickly.


Hey AtHome..any more local mets talking about this over our way??
Member Since: May 31, 2011 Posts: 57 Comments: 572
Quoting weatherh98:


Mandeville
Ah, the north side of Lake P. Getting any flooding yet?
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Quoting Charliesgirl:



the guy said the water was above the top of his doorframes and he is in one of the highest spots down there, he thought people in lower lying areas may have not been as lucky to get to the attic.

The woman in Braithwaite is still in her Attic with her mother and husband.
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Quoting AussieStorm:

The levee at Braithwaite got over-topped.
Here is the area. I did this quickly via Google Earth.



My dad said that was one of the big gates correct If wrong
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Quoting TampaFLUSA:
There are people trapped in their attics in Plaquemines Parish!


Cannot feel sorry..they were told to evacuate.
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1361. wjdow
Quoting vince1:

Slow down, and let's wait for Isaac to at least get on shore before fretting/wondering what's coming along next on the freight train. ;)
Quoting Thundercloud01221991:
is it possible since the eye is contracting that if/when Isaac pops back over water we can see him intensify to a cat 2 very quickly
The water's not deep enough for intensifying, is it? Where would the energy come from?
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1360. GetReal
I'll be back posting in and out over the next few hours... Currently we are experiencing the heaviest rains so far associated with Isaac... Reports of widespread street flooding starting to come in. The winds have remained a constant 45 to 60 mph with gust up to 80 mph....

I am observing some minor roof damage, and siding coming coming peeling off the side of homes. Easily 70% of the NOLA area is out of power now...
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Quoting leftlink:
Now that the eyewall is tightening to the south, it looks like winds south of the storm may increase, but I no longer see it drifting southwest toward open water. Not sure it is going anywhere soon at all. That convection might have prevented it from moving north, though. If the convection south of the storm continues to weaken or move east, then perhaps Issac will resume moving northwest.


so it is contracting...i thought i saw that.
Wonder what end effect the new convection blowup will be, it was a dying cyclone before that.
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Quoting indianrivguy:


Nice work Aussie! Good afternoon to you sir.

Don't call me sir, I work for a living, lol

Btw It's 9:40pm, Good Evening
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Quoting GeorgiaStormz:


judging from cams yesterday, it seemed like a lot of people still around so i hope its all okay.
Hopefully not too many died but i fear many may have stayed and be in trouble now.



the guy said the water was above the top of his doorframes and he is in one of the highest spots down there, he thought people in lower lying areas may have not been as lucky to get to the attic.
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Quoting Waltanater:
LOL...where is 'here'?


Mandeville
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Quoting AussieStorm:

The levee at Braithwaite got over-topped.
Here is the area. I did this quickly via Google Earth.



Nice work Aussie! Good afternoon to you sir.
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Now that the eyewall is tightening to the south, it looks like winds south of the storm may increase, but I no longer see it drifting southwest toward open water. Not sure it is going anywhere soon at all. That convection might have prevented it from moving north, though. If the convection south of the storm continues to weaken or move east, then perhaps Issac will resume moving northwest.
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1353. vince1
Quoting indianrivguy:


One eyed one horned flying purple people eaters?

Hang in there folks, everyone out here is pulling for you. Such conflicting feelings. Awesome to watch, sad to know their is serious suffering.

My my, how phosphorescent they must be. :0

And yup, could still be power-line related as weatherh98 surmised.
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pressure at 29.11
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Quoting weatherh98:
Pressure is 990.8 here and. Dropping
LOL...where is 'here'?
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1350. LargoFl

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS EXTENDED THE

* 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...
NORTHWESTERN PLAQUEMINES PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...PORT SULPHUR...BELLE CHASSE...
WESTERN ST. BERNARD PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF CHALMETTE...
ST. CHARLES PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF HAHNVILLE...
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Quoting GeorgiaStormz:


so are the pumps working down there?
So basically south of New Orleans is screwed but New orleans is fine?
That seems to be the impression im getting from reading back and checking the news

The levee at Braithwaite got over-topped.
Here is the area. I did this quickly via Google Earth.

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The pumps in NOLA are keeping up pretty good but this thing needs to move. Is the problem that there is no steering, or that the door to the North closed?
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Quoting Charliesgirl:



yes, these areas are out of the federal protection levees. The levees are made of dirt by the people who live there. They were under manditory evacuation but there is one guy trapped in his attic with his wife and baby, said he wanted to stay to save his stuff, though with a tropical storm it would be okay. he called the tv station, the 911 is overwhelmed down there.


judging from cams yesterday, it seemed like a lot of people still around so i hope its all okay.
Hopefully not too many died but i fear many may have stayed and be in trouble now.
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Pressure is 990.8 here and. Dropping
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Quoting interstatelover7165:
Person on my NBC station said hurricane IRENE on the Gulf Coast+Tampa.
Were they referencing Isaac or were they talking about a future storm, giving it a wrong name?
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Morning Wes, Charliesgirl, 98, all. Some harrowing tales out there. Stay safe over there. And I hope Isaac gets a move on quickly.
Member Since: August 24, 2010 Posts: 0 Comments: 254
Off for now Be Back later
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Quoting GeorgiaStormz:


so are the pumps working down there?
So basically south of New Orleans is screwed but New orleans is fine?
That seems to be the impression im getting from reading back and checking the news


That's the way I see it. Unfortunately, I live south of New Orleans (Jean Lafitte). I'm thankful we decided to heed the warnings and evacuate but am very concerned for friends and neighbors who didn't.
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Quoting Masquer08er:
Stop with the politics. And there has certainly been no shortage of media. Some of these areas have more media in them now, than residents.
No ones bringing politics on the damn blog.I just simply stated what the media cares more about.
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Quoting Masquer08er:
Stop with the politics. And there has certainly been no shortage of media. Some of these areas have more media in them now, than residents.
He is not being political. He is just making a statement, in his opinion that the media is covering one event more than the storm. The topic is really media, not politics.
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Quoting vince1:

Yikes. Transformers are typically green when bursting...wonder what the purple might represent.


One eyed one horned flying purple people eaters?

Hang in there folks, everyone out here is pulling for you. Such conflicting feelings. Awesome to watch, sad to know their is serious suffering.
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Quoting Waltanater:
KHAAAAAAANNN!!!!
Thanks! Been waiting for it. LOL
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Quoting interstatelover7165:
Person on my NBC station said hurricane IRENE on the Gulf Coast+Tampa.
Are they old and maybe reminencing?..lol
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1334. LargoFl
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Quoting GeorgiaStormz:


so are the pumps working down there?
So basically south of New Orleans is screwed but New orleans is fine?
That seems to be the impression im getting from reading back and checking the news



yes, these areas are out of the federal protection levees. The levees are made of dirt by the people who live there. They were under manditory evacuation but there is one guy trapped in his attic with his wife and baby, said he wanted to stay to save his stuff, thought with a tropical storm it would be okay. he called the tv station, the 911 is overwhelmed down there.
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Quoting washingtonian115:
Media cares more about republican convention then a hurricane affecting land.Oh well.Isaac must not be that big of a deal to them.
Stop with the politics. And there has certainly been no shortage of media. Some of these areas have more media in them now, than residents.
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Quoting GeorgiaStormz:
Is this westward jog lessening the surge over towards the mouth of the mississippi?
only lightly it will move north again soon
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Quoting GeorgiaStormz:
Is this westward jog lessening the surge over towards the mouth of the mississippi?


slowly the surge will come down but with it staying near the coast the surge will still be significant for quite some time
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Quoting trHUrrIXC5MMX:
LATEST ON KIRK...
_____________________________



the intensities wont be so if the storm keeps getting sheared...
KHAAAAAAANNN!!!!
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Is this westward jog lessening the surge over towards the mouth of the mississippi?
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Quoting Thundercloud01221991:
is it possible since the eye is contracting that if/when Isaac pops back over water we can see him intensify to a cat 2 very quickly

Cat 2 no,,,, not enough energy for that to happen.
Maintain intensity yes.
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Person on my NBC station said hurricane IRENE on the Gulf Coast+Tampa.
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Looks like the eye is just to the east 15 miles or so
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Quoting weatherh98:


Sounds like a damn train can't sleep
didn't know trains could sleep. LOL
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Quoting TropicalAnalystwx13:
TROPICAL STORM KIRK FORECAST/ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
0300 UTC WED AUG 29 2012

THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.

TROPICAL STORM CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
POSITION ACCURATE WITHIN 30 NM

PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB
MAX SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT.
34 KT....... 70NE 0SE 0SW 50NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
AT 29/0000Z CENTER WAS LOCATED NEAR 23.8N 44.5W

FORECAST VALID 29/1200Z 24.2N 46.6W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 0SE 0SW 40NW.

FORECAST VALID 30/0000Z 24.5N 48.6W
MAX WIND 50 KT...GUSTS 60 KT.
34 KT... 70NE 30SE 0SW 50NW.

FORECAST VALID 30/1200Z 25.0N 50.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 31/0000Z 26.0N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 01/0000Z 29.0N 55.3W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 50SE 30SW 60NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 175 NM
ON DAY 4 AND 225 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 02/0000Z 34.8N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.

OUTLOOK VALID 03/0000Z 42.3N 44.9W
MAX WIND 55 KT...GUSTS 65 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 23.9N 45.0W

NEXT ADVISORY AT 29/0900Z

$$
FORECASTER KIMBERLAIN/CANGIALOSI
Excellent! Our first catch of the day! (even though it was yesterday...LOL)
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Quoting AussieStorm:
2 stranded pump workers just now successfully rescued from levee in Braithwaite!


so are the pumps working down there?
So basically south of New Orleans is screwed but New orleans is fine?
That seems to be the impression im getting from reading back and checking the news
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1321. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
439 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* FLASH FLOOD WARNING FOR...
JACKSON COUNTY IN SOUTHERN MISSISSIPPI...
THIS INCLUDES THE CITIES OF...PASCAGOULA...MOSS POINT...
ESCATAWPA...

* UNTIL 730 AM CDT

* AT 431 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
VERY HEAVY RAINFALL LIKELY TO PRODUCE FLASH FLOODING ACROSS MOST OF
JACKSON COUNTY. FLOODING RAIN WATER NEAR THE COAST AND LOW LYING
BAYOUS...MARSHES...AND RIVERS WILL BE AUGMENTED BY MUCH HIGHER THAN
NORMAL TIDES.
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Quoting Autistic2:


Spending Billions and billions from storms in the same place IS weather related.

As for my timing you very well may be correct. Did not mean to put gas on a fire or um rain in a cain. Sorry to all.

My bad, I will bring thins up again in November or Dec.



Thanks
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is it possible since the eye is contracting that if/when Isaac pops back over water we can see him intensify to a cat 2 very quickly
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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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