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 hurricanehunter27:
I have to ask does anyone have rain totals from Isaac so far?


2.48

Pressure 990.5
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Quoting Jay5711:


New Iberia here.. Winds out the northwest (were out the northeast last night), no rain as of yet.. But wind picked up lil from last night lot more gusts


more gusty than earlier for sure - wind a little east of north - 1 very brief sprinkle around 3ish that was just enough to get things wet - already dried
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Quoting LargoFl:
Viewer sent this pic in to WDSU new orleans.......
hahaha someone is holding his feet which are conveniently not in the picture.
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1566. LargoFl
house in Mouton.....
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Quoting TropicalAnalystwx13:
With the exception of TS Alberto, every guy named storm this season has been a hurricane.

Chris...skip Debby...Ernesto...skip Florence...Gordon...skip Helene...Isaac...skip Joyce...Kirk?



what about the B storm?
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98L is looking better by the the hour. conditions are very conducive. there is good 850mb , 700mb and 500mb vorticity. 98L is moving in a low shear environment, with an anticyclone above the system.the shear forecast is expected to be in the 5-10 knot range for the next 4 days as it moves slightly north of west. 98L could develop into a depression the next 48 hrs,and then TS Leslie. all interest in the lesser antilles should monitor the progress of this system.
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Interesting Coverage:

http://www.fox8live.com/category/235642/watch-fox 8live
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Quoting TropicalAnalystwx13:
With the exception of TS Alberto, every guy named storm this season has been a hurricane.

Chris...skip Debby...Ernesto...skip Florence...Gordon...skip Helene...Isaac...skip Joyce...Kirk?
Kirk is supposed to become a Cat 1 now according to the NHC. Weird trend for sure.
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Quoting Masquer08er:
Pasa-something MS. Too funny! Around here folks say Pas-pa-goula (unless thats Pass Christian). Either way, I had a good laugh. Thanks


It's that landmass between Biloxi and Mobile. He should apply for a job with TWC.....lol
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1560. LargoFl
Biloxi miss...................
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1559. kwgirl
Good morning all. My thoughts and prayers are with all the people affected by Hurricane Isaac. Stay down and safe everyone. Even though this is a "minimal hurricane" the slow pace of the storm means the destruction will be cumulative. In other words, a roof that may have made it through a few hours of high winds may finally fail after days of high winds. Please keep in mind that after the storm, there will be a lot of hazards out there. A lot of storm deaths occur after the storm during clean up. The people of the Gulf Coast are a hardy bunch of people. You will make it through and I am sure your neighbors are poised ready to help in any way they can. Take care!
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Quoting AussieStorm:

Maybe they don't have either of what you have. Makes it easier for them, so what if it takes up a little blog space.



so ture
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1557. LargoFl
Pensacola beach..................
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With the exception of TS Alberto, every guy named storm this season has been a hurricane.

Chris...skip Debby...Ernesto...skip Florence...Gordon...skip Helene...Isaac...skip Joyce...Kirk?
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Quoting StormSurgeon:
Dauphin Island, AL has taken an extended beating from Isaac. Fully expect to find a real mess when we get back down to check on the house.
Maybe the pier will be back over water. I hope no more of the west end is lost.
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Quoting Masquer08er:
Pasa-something MS. Too funny! Around here folks say Pas-pa-goula (unless thats Pass Christian). Either way, I had a good laugh. Thanks


We do have some fun names for people from not around here or not familiar with French!
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Quoting Tazmanian:



ture but i can get too the nhc site on my android phone vary easy i can all so go too the nhc vary easy on my ipad some are this too lazy lol

Maybe they don't have either of what you have. Makes it easier for them, so what if it takes up a little blog space.
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1552. LargoFl
Montegut.................................
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Quoting SWLACajun:
Can someone post the latest track?



mode runs has not yet updated for 98L best too wait in tell the next update they still say 2am
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1550. icmoore
Quoting geecheegirl:


Cannot feel sorry..they were told to evacuate.


Well, you are a real sweetheart, aren't you!?! I am sorry people but it is not always an easy decision to make to leave your home and this season the models and forecasters have not gotten anything right until it's practically knocking on your door and that does nothing to help. Debby's going to Texas and Isaac was going to be the monster that ate FL...please try not to be so judgemental.
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1549. MTWX
Quoting presslord:
Spoke briefly to Pat's wife...they're alive and hunkered down....Anybody want a puppy?!


Sorry, just picked one up from auburn this last weekend... LOL!
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I have to ask does anyone have rain totals from Isaac so far?
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1547. ncstorm
I was watching GMA this morning and they were showing people in New Orleans at bars having hurricane parties until 12 in the morning..
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I think the latest short term track - Whatever ;-)
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Quoting AtHomeInTX:


Yep cone didn't move but track did. Hope it doesn't get too bad for ya.


I think as long as it doesn't drift more west we shouldn't be too bad. If it goes through Alexandria as the track stands, I'm about 45 miles west of there, so on the 'good' side. They're saying locally we'll probably lose electric, but we have all our supplies in if that happens.
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Can someone post the gsa track for 98L?
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Bay St. Louis: Sustained winds just above 43MPH. Gusting to 55mph. 9.1 feet above mean low water. Pressure at 996. Too windy to get good pictures.
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Dauphin Island, AL has taken an extended beating from Isaac. Fully expect to find a real mess when we get back down to check on the house.
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Quoting kctinney:


Think I googled my own answer: sufficient fuel to run the pumps for at least a day if electricity failed


that should be long enough...i think they still have power, if not, the flooding should be going own as isaac moves away in 24hrs
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Quoting AussieStorm:






guss some are this too lazy too go too the nhc site and look it up all so they can get the track the weather under ground has well
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Quoting Tazmanian:




you can go too the nhc site and see it on there or you can look back a few commets has it been post a lot of times on this pages or looks back a few pages

Taz, maybe they are on a mobile. easier if they see it here. Now is not the time to be like that, if people ask for info, give it.
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Quoting SWLACajun:
Can someone post the latest track?


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Quoting SWLACajun:
Can someone post the latest track?




you can go too the nhc site and see it on there or you can look back a few commets has it been post a lot of times on this pages or looks back a few pages
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Quoting WxNerdVA:
Oh wow, the NHC has Kirk as a hurricane now!



Looks like another Gordon situation.
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Quoting LargoFl:
Pasa-something Mississippi pic..some very Smart people here huh......................................
Pasa-something MS. Too funny! Around here folks say Pas-pa-goula (unless thats Pass Christian). Either way, I had a good laugh. Thanks
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1533. ncstorm
Good Morning..

Issac is making his mark on the gulf states. My prayers are with everyone down there.
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Quoting kctinney:


I have a question, if power goes out where the "best pump system in the world is"(lack of better term d/t just woke up), how long will the back up generators work or aren't they powered with electricty? TIA Sorry if a stupid question


Think I googled my own answer: sufficient fuel to run the pumps for at least a day if electricity failed
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Can someone post the latest track?
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1530. ge2655
Isaac’s hugging the gulf coastline is reminiscent of what he did along the Cuban coast, while approaching the Florida Keys

Regards,
-Gary
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Quoting ugajag:
Looks like Mobile is about to get some serious weather..
Thanks for the heads up!
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Long Beach, MS....about 2 1/2 blocks off of Hwy 90. Gusty with light rain. Highest wind gusts, per Univ. of Southern Miss (Gulf Park, 2 blocks to my west) weather station, has been up to 66mph. That makes the 110 gust in Louisiana very believable. Y'all stay safe over there in Louisiana! Our thoughts and prayers are with you!
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1526. palmpt
Quoting AussieStorm:

Your lucky. Look at this map.

My condo is next to a substation.
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Quoting CybrTeddy:
Heard that the storm surge overtopped the levees overnight, not good.

No federal levees have been overtopped, only some (1 that I know of in Plaquemines parish that is outside of the federal levee system, a couple of families that stayed are trapped with rising water around them.
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Quoting aislinnpaps:
Good morning, all. TWC said Baton Rouge will get hit hard. We're to get possible ITS winds later today and tonight. It appears the track has shifted a bit more west in the cone since last night?


Yep cone didn't move but track did. Hope it doesn't get too bad for ya.
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1523. LargoFl
Pasa-something Mississippi pic..some very Smart people here huh......................................
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Reading this it sounds like it will finally get moving. Heavy rains coming for central LA.

NATIONAL WEATHER SERVICE LAKE CHARLES LA
654 AM CDT WED AUG 29 2012

.DISCUSSION...
HURRICANE ISAAC HAS MADE LANDFALL IN SOUTHEASTERN LOUISIANA THIS
MORNING. ISAAC IS MOVING TO THE WEST NORTHWEST AROUND 6 MPH.
OUTER RAIN BANDS ARE SWEEPING ACROSS ST MARY PARISH AT THIS TIME
WITH LIGHT RAIN NOTED FROM AVOYELLES PARISH SOUTH INTO EASTERN
CAMERON PARISH. AS ISSAC MOVES TO THE NORTHWEST TODAY RAINS WILL
SPREAD SLOWLY ACROSS CENTRAL AND SOUTHWEST LOUISIANA. SINCE ISSAC
IS MOVING VERY SLOWLY THIS WILL CREATE THE POTENTIAL FOR RAINS TO
TRAIN ACROSS CENTRAL LOUISIANA WITH RAINFALL EVENT TOTALS ABOVE 10
INCHES IN SOME LOCATIONS.
RAINS WILL TAPER OFF FROM THE EAST TO
THE WEST WITH SOUTHEAST TEXAS ON THE WESTERN EDGE OF ISAAC`S RAIN
SHIELD... AND THEREFORE ONLY ONE MAYBE TWO INCHES IS EXPECTED FOR
SOUTHEAST TEXAS FOR THIS EVENT.

WINDS OVER BATON ROUGE WERE RUNNING AROUND 35 MPH WITH GUSTS TO 48
MPH. LAKE CHARLES IS REPORTING 16 MPH WITH GUSTS ABOVE 20 MPH AND
BEAUMONT IS REPORTING 20 MPH WITH GUSTS TO 25 MPH. WINDS WILL ALSO
GRADUALLY INCREASE THROUGH THE DAY AS ISAAC MOVES TOWARDS CENTRAL
LOUISIANA.

ISAAC WILL MOVE INTO WILL MOVE INTO CENTRAL LOUISIANA TONIGHT AND
INTO NORTHERN LOUISIANA WHERE IT WILL CONTINUE TO WEAKEN ON
THURSDAY AND ARKANSAS ON FRIDAY MORNING. THIS WILL SEE RAINS
FINALLY DRAWING TO A CLOSE.
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Quoting MAweatherboy1:

Yeah, lot of dry air on the whole west side of the storm, if you're west of the eye you're gonna get very little rain.


its always like that at landfall...air piling up on land and not as muc making it out back on the west side out to sea.

this could maintain intensity a lot longer if that deepest convection can wrap around
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Quoting Masquer08er:
I guess I have heard this (media shouldn't cover GOP convention during Isaac) so often on Twitter and social media that I'm over sensitive. This is the only site I can get weather discussion without politics. And, if politics gets brought in, virtually everybody stops it.
Understood. You are 100% right on that. I've seen it too.
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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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