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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1419. vince1
Fox 8 died, suddenly.

EDIT: Only temporary.
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Quoting NEFLWATCHING:
Chaser links, anyone?


www.stormjunkie.com
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Quoting kshipre1:
anyone have any thoughts as to where the next invest 98 might go? how is the upper air pattern looking?

Don't care.... Isaac is number 1 concern.
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Thoughts with everyone on The Gulf coast being affected. I'm sure last night must have felt like a really really long night and today will be an even longer day as those under Isaac wait for him to get a move on.

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1415. unc70
Quoting Unfriendly:


Yea.... no.

Please try and get a basic understanding of cyclones before you start posting about them. A strengthening Cat1 isn't about to relocate it's center... ever.


Never be too certain what any cyclone can not or will not do ... ever. The more we learn about hurricanes, the less we know (for certain). The systems are far to complex for any person or any system of computers to fully determine. Experience, research, and improved computer models have greatly improved 2-3 day forecasts; less so, 5 day or 5 hour. Isaac should humble most of us. When we see something "impossible", we must resist dismissing it as some equipment anomaly or an unreliable observation not from an official station.

As a counter example to your specific claim, I suggest Irene in and near NC. (Isaac reminds me a lot of Irene as it approached NC.)

Irene did it while "stalled" in the sounds around Morehead City and Beaufort, NC. It completed an eye-wall replacement cycle, had at least three competing vortices, and probably intensified to high Cat 2. It relocated its center from one eye to another (30+ miles). Not "officially" because all the official weather stations north of Topsail and south of Ocracoke had quit reporting over 2-3 hours before landfall. It was discussed a little on WU at the time.

Almost no one seemed to notice that station data was not updating, even here o WU. A big question is why did all the stations fail in TS conditions at nearly the same time? How did this impact preparedness in New England?

I will do a blog for later about the issues with Irene, the problems I have with what happened in NC, the failures of TWC and TV news to properly report, and concerns with NHC itself.

Good luck to all affected by Isaac.
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Checking in from Ascension Parish. Its getting bad here! I have a feeling power will be out momentarily. Winds have got to be gusting to 50-60mph right now.
And btw, Isaac has got to be the slowest moving storm ever...
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There is some significant levee over-topping but they seem to be holding.
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Quoting weatherh98:
I don't think I can get lakefrint pictures, there a tree one way and flooding the next street over.


have you been outisde at all?
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Quoting AussieStorm:

Last I heard, His bitch had 3 puppies. His phone was getting low and had no power.



yea...that was the last I heard, too...
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HURRICANE ISAAC TROPICAL CYCLONE POSITION ESTIMATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
700 AM CDT WED AUG 29 2012

...CENTER OF ISAAC WOBBLING INLAND OVER SOUTHEASTERN LOUISIANA...

AT 700 AM CDT...1200 UTC...THE CENTER OF HURRICANE ISAAC WAS
ESTIMATED NEAR LATITUDE 29.4 NORTH...LONGITUDE 90.5 WEST...OR
NEAR GALLIANO LOUISIANA. THIS IS ALSO ABOUT 20 MILES SOUTHEAST OF
HOUMA LOUISIANA AND ABOUT 50 MILES SOUTH-SOUTHWEST OF NEW ORLEANS
LOUISIANA. ISAAC IS HAS BEEN STATIONARY DURING THE PAST HOUR...BUT
A GENERAL MOTION TOWARD THE NORTHWEST NEAR 6 MPH...9 KM/H...IS
EXPECTED TO RESUME LATER THIS MORNING.

A SUSTAINED WIND OF 55 MPH WITH A GUST TO 70 MPH WAS RECENTLY
REPORTED AT NEW ORLEANS LAKEFRONT AIRPORT.

SUMMARY OF 700 AM CDT...1200 UTC...INFORMATION
------------------------------------------------- -
LOCATION...29.4N 90.5W
ABOUT 20 MI...30 KM SE OF HOUMA LOUISIANA
ABOUT 50 MI...75 KM SSW OF NEW ORLEANS LOUISIANA
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...970 MB...28.64 INCHES
Member Since: August 24, 2010 Posts: 0 Comments: 676
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...
try 75%. Mayor was on wdsu and confirmed it
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Chaser links, anyone?
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Quoting AussieStorm:

Last I heard, His bitch had 3 puppies. His phone was getting low and had no power.


i read this wrong at first..
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I don't think I can get lakefrint pictures, there a tree one way and flooding the next street over.
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Quoting presslord:
Anybody heard from Pat this AM? I can't get him on the phone....


He hasn't posted anything on the blog and I have been on since 4:30 AM
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anyone have any thoughts as to where the next invest 98 might go? how is the upper air pattern looking?
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Quoting presslord:
Anybody heard from Pat this AM? I can't get him on the phone....

Last I heard, His bitch had 3 puppies. His phone was getting low and had no power.
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1402. vince1
Seems the storm movement slowed from 6 to 5 mph since the last WU refresh (I noticed). Not a big difference but just more evidence of the lack of steering/direction.
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Isaac is Lining up to hit us
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IR image confirms that the convection boom south of the center is over. Now there is a new convection boom, just south of Alabama. Formed 20 minutes ago. GEOS-14 image now (7:50am):



If you cant see the image, get an update of new images here:

LINK
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Eye either closing off again, or filling in more and contracting..either way, not much change

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Quoting presslord:
Anybody heard from Pat this AM? I can't get him on the phone....


No but it reminds me to check on kori.
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1397. ADCS
This might be the worst possible track a storm could take for New Orleans.
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Quoting Charliesgirl:



I have power too. it has gone out a couple of times in the last hour, though. Slidell/PR area on the Northshore.
thats real good but this darn thing not moving!
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Quoting presslord:
Anybody heard from Pat this AM? I can't get him on the phone....



power is out too 70% of the city sol likey the phones are out too
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Quoting StormHype:
Live video inside the eye south of Chauvin LA:
Live video Link


Chris is way south of Chauvin LA near the end of 56. In the eye. 3g wireless is bad there, so it's up and down some. It's the edge of the world, and they still have power.
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Quoting barbamz:




Don't know whether it's the right layer, but the door to the north(-east) seems to be closed or too narrow.


If I got this right, the NHC said that the high to its NW would move east and the trough behind it would move it. And that would happen late today. It's a long tough ride. Hang in there guys.
Member Since: August 24, 2010 Posts: 0 Comments: 676
Anybody heard from Pat this AM? I can't get him on the phone....
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1391. LargoFl
causeway bridge lake P...................
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1390. roleli
See CNN webcams of french quarter in New Orleans
Link
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1389. barbamz
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Quoting washingtonian115:
1374 What ever man go back to suffering through your storm why I stay sunny and dry here in D.C.
Now why did I think the comment about the media was political?
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Just put on my best blue LL bean rain coat, shaved my head, and stole 1 of my kids toy microphones. I'm going outside to stand n the wind and rain to talk about the same thing over and over again. Being certain to state my concern about the stop sign flapping in the wind. Lol. Really though it's beginning to get pretty tough here.
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Isaac looks better defined than last night.

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1385. barbamz
Quoting Grothar:
98L



Gro, nice to see you. I've missed you yesterday, but I couldn't read all the posts. How things are going? Still flooded?
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2 trees down that I can see siding ripped off and shingles missing
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1383. hydrus
Quoting weatherh98:


Mandeville Louisiana

North of new orleans
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.
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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
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Quoting xtremeweathertracker:


Hey AtHome..any more local mets talking about this over our way??


Hadn't heard a word. I hope it gets moving somewhere soon.
Member Since: August 24, 2010 Posts: 0 Comments: 676
Check out dozens of twitter feeds from people located in Houma, the first populated area that the eye is going to go over...

http://twitter.com/#!/search/?q=houma&src=typd

For example:

http://twitter.com/poorchelsea
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Amazing.... Lafayette just miles from the eye and its nice here.... been sitting on patio with just a nice breeze. I realize this is the west side. Anyone think it will get bad here?
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1377. Grothar
98L


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Quoting geecheegirl:


Cannot feel sorry..they were told to evacuate.

The woman and her mother and husband stuck in their attic are stuck due to their truch breaking down yesterday. so they stayed as the had no other way of leaving


This is lake front.



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1375. LargoFl
Bourbon st cam...........
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1373. LargoFl
Quoting bigwes6844:
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
yeah its pretty bad there..wish this storm would move but looks like it doesnt know where to go to..
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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...


Thanks GetReal. Stay safe. I hope it's over for all of you soon.
Member Since: August 24, 2010 Posts: 0 Comments: 676
1371. barbamz
Quoting Charliesgirl:
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?




Don't know whether it's the right layer, but the door to the north(-east) seems to be closed or too narrow.
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I suppose Grand Isle is way under...
I cant seem to get anything straight from the news
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Quoting geecheegirl:


Cannot feel sorry..they were told to evacuate.
Cyborgs don't feel pain.
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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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