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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1869. LargoFl
Quoting WDEmobmet:
longbeach is in mississippi
ok, just saw a post on twitter..the water in the canals in MISS are rising also
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1868. MahFL
Quoting DavidHOUTX:
Unbelievable..



If you have ever visited NO it's not really unbeleivable as a lot of housing is either below sea level or only 5 or 6 feet above sea level, so with a 13 ft surge and 8 ft levee's your house is going to be flooded.
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Quoting MTWX:


As long as the strong winds direction keep coming onshore, the surge will continue. It won't start going down until the winds slow or change direction.

Hope this helps.


Thanks.... Just sitting in Houma waiting too see what he is gonna do. No rain light breeze from the north.
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Quoting Thing342:
I don't have any pics, but basically recurve east of Bermuda as a strong TS/weak Cat 1


Ok, thank you...glad it's not coming into the gulf!
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7544....still have cell service in Long Beach...just west of Gulfport.
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1864. LargoFl
Quoting Waltanater:
Really!? A life vest!? c'mon...
idiot post
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longbeach is in mississippi
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Quoting MTWX:


Presslord talked to Patrap this morning. (his dog had puppies last night)

Noone has heard from tkeith so far this morning...

StormJunkie is live in Biloxi.. Link


MTWX~~ thank you for letting me know. They are such good folks. My prayers are with them. Wonder what kind of puppie? Hope to see them on here soon.

sheri
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Quoting ProgressivePulse:


Seriously, all homes in flood zones should be equipped with emergency exit hatches and/or tools in the attic.
Those could also be a weak point for wind and rain in a storm. Better to have an axe and crowbar at the ready.
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Quoting tater5500:
...anyone have the runs on what Kirk is going to do?
I don't have any pics, but basically recurve east of Bermuda as a strong TS/weak Cat 1
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1858. ncstorm
So if Im understanding correctly, the levees outside the Federal Govt are breeching..
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1857. Skyepony (Mod)
Waveland is at peak too..over 9'.

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1856. 7544
gulfport just had 76mph in gulfport are cell phones working in that area anyone know tia
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...anyone have the runs on what Kirk is going to do?
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Quoting LargoFl:
Longbeach......wish they would put what state.
Long Beach looks more like Long Island.
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Quoting TxGrandma:


David, where is this?


Plaquemines Parish
Member Since: August 18, 2011 Posts: 0 Comments: 635
One of my fav's...the wind map


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1850. MTWX
Quoting LargoFl:
Longbeach......wish they would put what state.


That would be Mississippi.
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1849. LargoFl
people stuck on a levee
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Largo...that's the Burger King in Long Beach, MS, across from our harbor. It's on Hwy 90.
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Quoting LargoFl:
..in the eye itself it seems..sun may even come out there..hope they dont relax
They'll have time to do a few push-ups outside! LOL
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Quoting DavidHOUTX:
Unbelievable..



David, where is this?
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We should get a full advisory from the NHC on Isaac within the next half hour, I'm guessing they'll keep the winds at 75mph.
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1844. LargoFl
Longbeach......wish they would put what state.
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1843. Skyepony (Mod)
This should be about peak surge in Grand Isle, right now as high tide is occurring..

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1842. LargoFl
twinspan bridge in NOLA
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1841. ncstorm
Quoting SrChiefFan1:


His home has had enough damage that it is destroyed. The mold alone will require it to be razed...

Let's see how all of you desk jockey weather wishers would handle what he and his area is experiencing and see how you would react. Get off his freaking back...


from his mouth..nothing says his house is destroyed..and no one is on his back..complain later..get the people out now!..

Water pushed by the large and powerful storm flooded over an 18-mile stretch of one levee in Plaquemines Parish south of New Orleans, flooding some homes in a thinly populated area. No injuries were reported. "When this is over, I think we need to check the wind speeds because I lost a good portion of my roof, my fence is down, and water is blowing through the sockets in my house from the back wall," Parish President Billy Nungesser said in a phone call to CBS New Orleans affiliate WWL-TV. "That only happened in Katrina."
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1840. MTWX
Quoting catastropheadjuster:
Hey Has anyone heard from Pat,StormJunkie or any other folks from NO?

Sheri


Presslord talked to Patrap this morning. (his dog had puppies last night)

Noone has heard from tkeith so far this morning...

StormJunkie is live in Biloxi.. Link
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Unbelievable..

Member Since: August 18, 2011 Posts: 0 Comments: 635
1838. LargoFl
HE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* TORNADO WARNING FOR...
EAST CENTRAL WASHINGTON PARISH IN SOUTHEAST LOUISIANA...
NORTHEASTERN HANCOCK COUNTY IN SOUTHERN MISSISSIPPI...
PEARL RIVER COUNTY IN SOUTHERN MISSISSIPPI...

* UNTIL 945 AM CDT

* AT 909 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 21 MILES SOUTHEAST OF MCNEIL...OR 9 MILES NORTH OF DIAMONDHEAD...MOVING NORTHWEST AT 70 MPH.
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Quoting CybrTeddy:
The thing about this storm as to why it is so destructive is because it's not going anywhere in a hurry, Katrina and Gustav where there and gone within a day, this thing is barely on the coastline and still as strong as it was last night and it came in at a very bad angle for storm surge. Watched a video of a man calling in from Plaquemines Parish saying that the surge had gone all the way up to their attic and they where going to have too shoot a hole through the roof to get out. Seems the general shock and disbelief was that Isaac was only a Category 1 hurricane per the news.


I don't know what local authorities were telling people in that area, but most hurricane experts were very concerned about the flooding.

We've learned in the past that a very large, slow moving tropical storm or CAT 1 can still create storm surge closer to CAT 2 or CAT 3, especially if it takes a bad angle to the targeted landfall.
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1836. jpsb
Quoting SELAliveforthetropic:
I have a question, once a storm makes landfall the surge comes, the surge happens just that once or can it keep coming as long as it is part over water? I hope that makes sense.
The wind can pile up water, but it is my understanding that the surge is a dome of water under the low pressure around the eye. The lower the pressure the high the dome. But if the winds are on shore before the eye gets there then the winds can pile up the water so that the dome rides on already high water. And a big slow moving storm with high winds can pile up a lot of water.
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Quoting catastropheadjuster:
Hey Has anyone heard from Pat,StormJunkie or any other folks from NO?

Sheri


Press posted earlier that he had spoken with Mrs. Pat and all is well - no power and hunkered down with the new puppies.
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1834. LargoFl
Quoting leftlink:
It is bright out in Houma, here is pic 8 minutes ago:

..in the eye itself it seems..sun may even come out there..hope they dont relax
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Quoting LargoFl:
I have really learned one thing this last week, there is no such thing as "its just a tropical storm"..or its just a weak cat-1"...anything tropical can destroy your house and change your lives..remember the comments just a day ago in here..aw it doesnt even look like its going to form into a hurricane..aww it looks terrible etc..people read that..and relaxed when in stead they should have been hurriedly preparing, boarding up etc and maybe even getting out of town...today we have a guy saying he didnt get this much damage in katrina...today he's hurting..every storm is different..no matter if it IS.."just a tropical storm"

Yup! Tropical storms are tasked with redistributing equatorial energy and taking it poleward. It uses water to do this. Code improvements have made wind less of an issue, but water from a TROPICAL storm is going to dump and push a lot of water. It's just a matter of forward speed where that water goes. S-S scale is almost useless now, and we need some serious consideration of the IKE.
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1832. MTWX
Quoting SELAliveforthetropic:
I have a question, once a storm makes landfall the surge comes, the surge happens just that once or can it keep coming as long as it is part over water? I hope that makes sense.


As long as the strong winds direction keep coming onshore, the surge will continue. It won't start going down until the winds slow or change direction.

Hope this helps.
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1831. LargoFl
Quoting truecajun:


we have an ax in the attic, but I never thought about life jackets. duh! need to get those - especially since our 2 youngest can't swim. we are behind a Mississippi River levee near Baton Rouge.
..good for you..we are all learning from this storm, its showing us things we didnt think about before
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Quoting leftlink:
It is bright out in Houma, here is pic 8 minutes ago:



That would be the eye of the storm per radar.
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Quoting weatherh98:


Trust me it's bad


sorry for you. yuck. does the rain stop and start or is it pretty much constant now?
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It is bright out in Houma in the eye, here is pic 8 minutes ago from twitter.com/NewsCarolyn:

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The thing about this storm as to why it is so destructive is because it's not going anywhere in a hurry, Katrina and Gustav where there and gone within a day, this thing is barely on the coastline and still as strong as it was last night and it came in at a very bad angle for storm surge. Watched a video of a man calling in from Plaquemines Parish saying that the surge had gone all the way up to their attic and they where going to have too shoot a hole through the roof to get out. Seems the general shock and disbelief was that Isaac was only a Category 1 hurricane per the news.
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These storms - whether TD, TS, Hurricane Typhoon - and the sea are nothing to fool with. One day people will finally learn that you cannot win against them. There is absolutely NO reason to risk you life - NO reason not to get out of harms way. Loss of life in these situations is so tragically unnecessary. I love the beach - would love to live near the coast - I can assure you that I would be ready to evacuate when it was necessary. Houses can be replaced - you life can't and what have you gained if you stay to protect your property and loose your life???? Sorry, It's just plain stupidity not to evacuate these areas - no excuse - no reason!
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Hey Has anyone heard from Pat,StormJunkie or any other folks from NO?

Sheri
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Quoting LargoFl:
yes everyone tries to prepare according to what they might have went thru over the years..but people forget..each and every storm is different..you made it thru 5 storms..ok..but maybe not This one huh..prepare for the worst..and if it does come to you..you..ARE prepared for it..me im seeing what is happening in the northern gulf..and im adding one thing to my prepare package..a life vest..cannot believe a 16 foot storm surge..or higher maybe..stranded on a rooftop?..uh uh..not me


we have an ax in the attic, but I never thought about life jackets. duh! need to get those - especially since our 2 youngest can't swim. we are behind a Mississippi River levee near Baton Rouge.
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1823. hercj
Sorry I got the quote wrong. I am still asking the question of Reedzone.
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BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
915 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* TORNADO WARNING FOR...
EAST CENTRAL WASHINGTON PARISH IN SOUTHEAST LOUISIANA...
NORTHEASTERN HANCOCK COUNTY IN SOUTHERN MISSISSIPPI...
PEARL RIVER COUNTY IN SOUTHERN MISSISSIPPI...

* UNTIL 945 AM CDT

* AT 909 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 21 MILES
SOUTHEAST OF MCNEIL...OR 9 MILES NORTH OF DIAMONDHEAD...MOVING
NORTHWEST AT 70 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
CROSSROADS

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THE SAFEST PLACE TO BE DURING A TORNADO IS UNDER A WORKBENCH OR OTHER
PIECE OF STURDY FURNITURE. SEEK SHELTER ON THE LOWEST FLOOR OF THE
BUILDING IN AN INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET. USE
BLANKETS OR PILLOWS TO COVER YOUR BODY AND ALWAYS STAY AWAY FROM
WINDOWS.

IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A
SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE
NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.

PLEASE FOLLOW OUR OFFICE ON BOTH FACEBOOK AND TWITTER FOR MORE
INFORMATION ON SEVERE WEATHER AND TO RELAY WEATHER REPORTS AND
PHOTOS.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 400 PM CDT WEDNESDAY
AFTERNOON FOR SOUTHEAST LOUISIANA AND SOUTHERN MISSISSIPPI.

&&

LAT...LON 3064 8934 3049 8934 3044 8940 3082 8990
3092 8972
TIME...MOT...LOC 1416Z 134DEG 59KT 3059 8944

$$

MJH
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I have a question, once a storm makes landfall the surge comes, the surge happens just that once or can it keep coming as long as it is part over water? I hope that makes sense.
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1820. LargoFl
I have really learned one thing this last week, there is no such thing as "its just a tropical storm"..or its just a weak cat-1"...anything tropical can destroy your house and change your lives..remember the comments just a day ago in here..aw it doesnt even look like its going to form into a hurricane..aww it looks terrible etc..people read that..and relaxed when in stead they should have been hurriedly preparing, boarding up etc and maybe even getting out of town...today we have a guy saying he didnt get this much damage in katrina...today he's hurting..every storm is different..no matter if it IS.."just a tropical storm"
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Quoting MAweatherboy1:
Quite a contrast between the two sides of the storm, if you're on the east side you're getting soaked, if you're on the west side you're dry.



Unfortunately New Orleans is on the east side.


I'm on the West side, and it is very dry and windy. There has been a misty sprinkle here and there. The driveway is dry.
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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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