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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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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2 stranded pump workers just now successfully rescued from levee in Braithwaite!
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Quoting bigwes6844:
Just now waking up and suprise i still have power. But i was just heard that Plaqumines parish has about 16 feet of its levee overtopped and people have been stranded on the levee and in their houses with 12 feet of water in it. It is a small town of Braithwaite near st. bernard and plaqumines parish. This weather is getting worse here in Nola folks but we are okay



I have power too. it has gone out a couple of times in the last hour, though. Slidell/PR area on the Northshore.
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Quoting GeorgiaStormz:


it almost looks like it was a dying cane and now its strengthening again..

are you safe up there?
Ive heard there is flooding practically everywhere but new orleans, but all the different media seem to have a different idea of how bad this is



I haven't done a flood check yet because of the lack of light, however the lakefront is more than likely under two feet and it's still an east wind
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Quoting IcemanMC:



THis is a weather blog and is certainly not the time for this conversation


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.
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1314. LargoFl
ULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
620 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* TORNADO WARNING FOR...
HARRISON COUNTY IN SOUTHERN MISSISSIPPI...
THIS INCLUDES THE CITIES OF...LONG BEACH...GULFPORT...BILOXI...

* UNTIL 645 AM CDT

* AT 612 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
TWO SEVERE THUNDERSTORMS CAPABLE OF PRODUCING A TORNADO...ONE NEAR
LYMAN...AND ANOTHER 4 MILES SOUTH OF BILOXI...MOVING NORTHWEST AT
55 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
GULFPORT AIRPORT.
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Quoting weatherh98:


Sounds like a damn train can't sleep


it almost looks like it was a dying cane and now its strengthening again..

are you safe up there?
Ive heard there is flooding practically everywhere but new orleans, but all the different media seem to have a different idea of how bad this is
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1312. LargoFl
Quoting IcemanMC:



THis is a weather blog and is certainly not the time for this conversation
agreed,this isnt the time for this, recriminations can come later when all are safe
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1311. vince1
Quoting CaribBoy:
So by by 98L.... now where is 99L??

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. ;)
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LATEST ON KIRK...
_____________________________



the intensities wont be so if the storm keeps getting sheared...
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I'll be on in a few hours everyone in my area stay safe!
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Quoting drg0dOwnCountry:


Maybe this?

Purple Flashing Lights: New Way to Indicate Emergency
With the power out the only thing it could really be is the power lines themselves
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Live video inside the eye south of Chauvin LA:
Live video Link
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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.

It's what if more new worthy to the greater public.
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That last convection blowup certainly isnt helping this weaken any....wonder how long it will keep up this intensity
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Quoting Autistic2:


Then please do Not count on the rest of us to rebuild a below sea level area every couple of years!




THis is a weather blog and is certainly not the time for this conversation
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So bye bye 98L.... now where is 99L??
Member Since: October 6, 2007 Posts: 0 Comments: 5929
Quoting weatherh98:
There was just a purple light that flashed twice outside, I

Aliens.

No power everywhere is so messed up. You can see another now, lights are going out in a hurry now


Maybe this?

Purple Flashing Lights: New Way to Indicate Emergency
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Quoting GeorgiaStormz:
Good morning guys, whats going on with isaac right now?


Sounds like a damn train can't sleep
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I hope this doesnt start moving north in the next hour, I'd be stuck in the eye wall and it would push water. Consistently into my are with around 8-12 feet of water going in.
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Good morning guys, whats going on with isaac right now?
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Quoting weatherh98:
There was just a purple light that flashed twice outside, I

Aliens.

No power everywhere is so messed up. You can see another now, lights are going out in a hurry now


Transformers blowing up maybe?
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WITH REGARDS TO DEVELOPING LOW ACROSS THE TROP ATLC...AN OSCAT/OCEANSAT-2
PASS AROUND 0140Z SHOWED A BROAD LOW JUST SOUTH OF 12N AND 31.5W
WITH A BAND OF 30+ KNOT UNCONTAMINATED WINDS. SO THE SYSTEM IS
GETTING ORGANIZED IN A HURRY DESPITE ITS LARGE SIZE. SFC PRESSURES AT
BUOY 41041 LOCATED NEAR 14.2N AND 46.0 HAVE BEEN FALLING STEADILY
SINCE 15Z TUE WITH A NORTH WIND NOW INDICATING THAT THIS SYSTEM IS
STRENGTHENING AND GETTING BETTER ORGANIZED BY THE MINUTE. MODELS
SHOW A POLAR TROUGH DIGGING ACROSS THE NW ATLC OVR THE WEEKEND
WHICH SHOULD WEAKEN THE RIDGE ENOUGH TO ALLOW THE DEVELOPING
SYSTEM TO SCOOT TO THE NW BEFORE REACHING THE ISLAND CHAIN. OF THE
20 GFES ENSEMBLE PERTURBATIONS ONLY THREE SHOW THE SYSTEM PASSING
OVER THE USVI WITH THE REMAINING OTHER RECURVING THE SYSTEM BEFORE
IT REACHES 60W. DUE TO THE EXPECTED STRENGTHENING AND LARGE
CIRCULATION THE SYSTEM WILL GENERATE LARGE SWELLS THAT WILL
EVENTUALLY REACH OUR ATLC COASTLINE CREATING DANGEROUS SURF CONDITIONS.


Crap! We don't need strong swells! I hate that trough. Why was it absent to bring me rain with Isaac, TD7, and Ernesto!! They were having so much difficulties to climb and even lost latitude around the islands! So really, WTF with that!!! We won"t get rain til october if everything develop and become a fish. Really boring guys.
Member Since: October 6, 2007 Posts: 0 Comments: 5929
Entergy now estimating 434,500 without power in SE Louisiana due to #Isaac.
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Quoting hydrus:
Where are you located 98.?


Mandeville Louisiana

North of new orleans
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Media cares more about republican convention then a hurricane affecting land.Oh well.Isaac must not be that big of a deal to them.
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High tide comes in late morning so its bound to get a little worse.
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1290. LargoFl
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1289. hydrus
Quoting weatherh98:
There went another tree.
Where are you located 98.?
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Quoting vince1:

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


I've seen purple for a transformer but it could be the line itself busting
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Another power flash
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1286. vince1
Quoting weatherh98:
There was just a purple light that flashed twice outside, I

Aliens.

No power everywhere is so messed up. You can see another now, lights are going out in a hurry now

Yikes. Transformers are typically green when bursting...wonder what the purple might represent.
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1285. LargoFl
eastward its pretty bad there also, lots of tornado's etc..this storm is huge, hitting several states at the same time whew
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Quoting nrtiwlnvragn:









Fox8 mod just said all the buoys south of NO failed.
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1283. barbamz
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There was just a purple light that flashed twice outside, I

Aliens.

No power everywhere is so messed up. You can see another now, lights are going out in a hurry now
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No eyewall replacement cycle... instead the storm is undergoing a LEGR (Loose Eye Regeneration Cycle).

Expect to see 961Mb pressure when Recon gets their barometer fixed!

This is why I don't think it is going onshore soon, but instead it is slowly intensifying and expanding in area as it did all yesterday:

4:41am CDT:


5:21am CDT:


5:41am CDT:


Unfortunately, the images stopped coming after 5:41am, this page is operating intermittently today.
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Quoting tjboudreaux:


If you think the government is going to exile descendants of the Acadians, you really don't understand us, or our love for our culture. Please keep such an opinion to yourself. I'm here to get up to the minute info for my family and friends, not read comments like that.
Have this discussion after everyone is safe.
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1279. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE JACKSON MS
553 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHERN FORREST COUNTY IN SOUTHEAST MISSISSIPPI...

* UNTIL 630 AM CDT

* AT 553 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 9 MILES
SOUTHEAST OF MAXIE MOVING NORTHWEST AT 50 MPH.

* THE TORNADO WILL BE NEAR...
MAXIE BY 600 AM CDT...
BROOKLYN BY 605 AM CDT...
ROCK HILL BY 615 AM CDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A TORNADO WARNING MEANS THAT A TORNADO IS OCCURRING OR IMMINENT. YOU
SHOULD ACTIVATE YOUR TORNADO ACTION PLAN AND TAKE PROTECTIVE ACTION
NOW.

HEAVY RAINFALL MAY OBSCURE THIS TORNADO. TAKE COVER NOW! IF YOU WAIT
TO SEE OR HEAR IT COMING...IT MAY BE TOO LATE TO GET TO A SAFE PLACE.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 700 AM CDT WEDNESDAY MORNING
FOR SOUTHERN MISSISSIPPI.

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Quoting LargoFl:
..looks like the eye is sitting half on land, half on water, just sitting there like in no hurry to come fully ashore,NOLA is on its Bad northeast side, whew, the flooding is going to be a disaster im afraid., storm surge is higher than gustav's and still coming in news reports say
that's not good!

I'm on the Nola side an it ain't gonna stop soon. Surge here is already worse than Gustav. Every 20 minutes the house shakes and BOOM a tree falls!

Pretty cool actually
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1277. ugajag
6am..
29.4
90.5
nw@6
80mph
970mb

Movement from wnw to nw..moved 1 degree to the east..
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Quoting weatherh98:
The power went off for the last time last night at 10:31

It's like trying to sleep in a carwash

It's LOUD and the rain is pelting my window.

Can someone gimme a condensed version of what's going on right now as I can't do analysis


not any good news,its moved about 50 miles in the last 12 hours,mainly to the west,right along the coast,the eye is still over water( gulf and wetlands),its blocked by high pressure to the north,looks like it just going to drift west or wnw for many hours.
Stay safe,it could be a long wait.
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1275. LargoFl
Quoting weatherh98:
The power went off for the last time last night at 10:31

It's like trying to sleep in a carwash

It's LOUD and the rain is pelting my window.

Can someone gimme a condensed version of what's going on right now as I can't do analysis
..looks like the eye is sitting half on land, half on water, just sitting there like in no hurry to come fully ashore,NOLA is on its Bad northeast side, whew, the flooding is going to be a disaster im afraid., storm surge is higher than gustav's and still coming in news reports say
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1274. barbamz
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Quoting Autistic2:
Perhaps the time has come to give up on new Orlens and sourounding areas. Just to low. Mother nature allways wins. Thankfully this is a very low cat one. It could have easly been a 2 or threee.

The way we spend money (USA) we could buy all that land and make it some sort of national park or wildlife reserve. Yes it would be a painfull process to the people moving but not as painfull as dieing in your atrtic.

Hopefull this will be an isolated case.

Thank God he did n ot really spin up.


If you think the government is going to exile descendants of the Acadians, you really don't understand us, or our love for our culture. Please keep such an opinion to yourself. I'm here to get up to the minute info for my family and friends, not read comments like that.
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1272. MahFL
TV is back.
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Where you see green on a louisiana map down in the southern part, remember its mainly vegetation sitting in shallow water, it's not exactly land
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Plaquemines Parish just successfully rescued 3 people from rooftop in Braithwaite. Residents & rescuers both safe! More to go though....
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1269. MahFL
The TV station just went off the air.
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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.