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 wxchaser97:

I heard a number around that, I could see even more with what Isaac has done so far. As for the re curve I don't know if that is true or not.


There were several ppl that said that on the comments after several of Dr. M's blogs and I look to see how often those individuals post to determine if I should give their info any credibility or not and that's what I recall....(granted I am sleep deprived and just took a Restoril so not positive! HAHA
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Quoting zillaTX:


He just does not want to give in, going all rounds!


he finally grew a nutsack.
Member Since: September 18, 2010 Posts: 0 Comments: 5115
Quoting HurricaneHunterJoe:
according to NHC standards i guess........anyone know that standard? the whole eye part of the eye touches land? im not sure.
It is once the center of the eye(not eyewall) comes ashore then the TC has made landfall.
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Quoting Momnick8BR:
New Orleans outages

Link


sounds like 1/2 of N.O. power out. wasnt it like 200,000? how many paying customers in greater N.O.?
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Quoting kctinney:


If I recall correctly, didn't they say approx 500,000 would be without power when Isaac was done and NO has MANY MANY hours left of Isaac.

In addition, I don't claim to know much re hurricanes however I do read MANY of the posts and several ppl on here have indicated that when a hurricane stalls in the Gulf it "normally" has a tendency to curve back to the RIGHT meaning East.

I heard a number around that, I could see even more with what Isaac has done so far. As for the re curve I don't know if that is true or not.
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Quoting NJcat3cane:
it appears atleast a portion of the northren eyewall was moved inland now..offical second US landfall?
according to NHC standards i guess........anyone know that standard? the whole eye part of the eye touches land? im not sure.
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Intermediate Advisory 32B to be issued soon...
That will tell us all.
Member Since: September 7, 2006 Posts: 89 Comments: 2653
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Quoting wxchaser97:
One last thing, over 310,000 people without power in Louisiana.


If I recall correctly, didn't they say approx 500,000 would be without power when Isaac was done and NO has MANY MANY hours left of Isaac.

In addition, I don't claim to know much re hurricanes however I do read MANY of the posts and several ppl on here have indicated that when a hurricane stalls in the Gulf it "normally" has a tendency to curve back to the RIGHT meaning East.
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1010. Reb74
Here in NWFl, no real rain, just lots of wind. Driest hurricane ever as far as rainfall amounts. Lots of wind-driven salt water but very little fresh. Strange indeed.
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Quoting NJcat3cane:
it appears atleast a portion of the northren eyewall was moved inland now..offical second US landfall?

Possibly? Met on WDSU just stated he sees a n jog possibly ne. Guess we will see soon enough:)
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Quoting Elena85Vet:


Sure is. Can't wait for the explanation on why Isaac did the things he did.



I think what he did is chew on a large percentage of the SAL that was present across the Atlantic Basin....if you look at the SAL maps prior to Isaac pumping the ridge compared to now you can see he ate it....and he stacked up anyway,....in a way i see him as a mixed ice cream cone....the chocolate is the rain/moisture and the vanilla is the dry SAL....and its all swirled together around the eyewall and across the different strata of the atmosphere....

notice how Jim Cantore smelled that burning smell in the air like I said earlier...he said it on tv and i was like finally at least im not fu**in crazy or just smelling my own upper lip....lol

i wonder what the burnt smell was in the air....it may be the chemicals and burn off from the oil and the smell of the dispersements????i dunno but it definately smells different than any hurricane/trop storm i have ever been around....


back outside to see clouds just 30 ft over my head go flying by me real fast....its freakin cool looking but it reminds me of....tornados....oh well, gonna go watch it....brb in a few :)
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Currently, Isaac's ACE is 7.6675. Isaac is 0.0375 short of Ernesto's ACE (7.7050), and 0.5225 short of Gordon's ACE (8.1900). If Isaac is 75 kt at the next advisory, it will be first place in ACE. Even if it's 70 kt, the advisory after the next will make it first place.

Atlantic's current ACE is about 33, while the Eastern Pacific's current ACE is 62.6. (LOL)
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1006. zillaTX
Quoting AllStar17:
Latest vortex (and likely last by this recon) has a 968 mb storm...holding its own right now.


He just does not want to give in, going all rounds!
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Quoting WetBankGuy:


Things have calmed down a bit (except for squalls)since the last reading at the New Basin Canal. And now there's that huge gap on the radar on the west side where the circulation was closed from a radar view for quite a while.


I have had steady rain and wind in Terrytown since 7pm
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Quoting AllStar17:
Latest vortex (and likely last by this recon) has a 968 mb storm...holding its own right now.



even without real strong winds there is going to be substantial property damage due to Isaac....Water is coming in sideways and is going to pour for days and days....loosening of the soil is going to allow trees to fall on covered property.....trees in la oftentimes root very shallow,......sustained winds of 70-80 gusting over days and days will do considerably more damage to a structure than a quick storm doing 100 gusts.....the wind will rip and tear rip and tear as water tries to pour/blow/whip in.....i do agree with the potential cost of Isaac in the $B's....
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Quoting odinslightning:
Here around Mobile/Tillmans border we have received rain but no real severe winds....more like a large rainstorm to us here so far....I know it has been different across the bay, it's just the dry air pocket feeding in set up over the western shores for hours and hours here in Bama......

Isaac is the most tropical hybrid I have ever seen in my life....I am sure there are other storms similar, but to hit the north gulf coast at the end of august with this size, very cold winds and rain, and so much dry air.....Isaac is an oddball to say the least.....


Sure is. Can't wait for the explanation on why Isaac did the things he did.

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Quoting AtHomeInTX:
I wouldn't look for any track changes coming up from this wording. But I could be wrong. It has happened. :)

HURRICANE ISAAC TROPICAL CYCLONE POSITION ESTIMATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
100 AM CDT WED AUG 29 2012

...CENTER OF ISAAC STILL OVER WATER...

AT 100 AM CDT...0600 UTC...THE CENTER OF HURRICANE ISAAC WAS
ESTIMATED NEAR LATITUDE 29.0 NORTH...LONGITUDE 90.0 WEST...OR ABOUT
60 MILES SOUTHEAST OF HOUMA LOUISIANA...AND ABOUT 70 MILES SOUTH OF
NEW ORLEANS LOUISIANA. ISAAC HAS MOVED LITTLE OVER THE PAST COUPLE
OF HOURS...BUT A SLOW NORTHWESTWARD MOTION IS EXPECTED TO RESUME
LATER THIS MORNING.

A SUSTAINED WIND OF 62 MPH WITH A GUST TO 71 MPH WAS RECENTLY
REPORTED AT SHELL BEACH LOUISIANA. A SUSTAINED WIND OF 57 MPH WITH
A GUST TO 79 MPH WAS REPORTED WITHIN THE PAST HOUR AT PILOTTOWN
LOUISIANA. A SUSTAINED WIND OF 54 MPH WITH A GUST TO 68 MPH WAS
REPORTED AT NEW CANAL STATION IN NEW ORLEANS. A WIND GUST TO 80
MPH WAS REPORTED BY A HAM RADIO OPERATOR AT ALGIERS IN JEFFERSON
PARISH LOUISIANA.

A STORM SURGE OF 4.3 FEET WAS RECENTLY REPORTED AT A NATIONAL OCEAN
SERVICE TIDE GAUGE AT NEW CANAL STATION ON THE SOUTH SHORE OF LAKE
PONTCHARTRAIN.


Things have calmed down a bit (except for squalls)since the last reading at the New Basin Canal. And now there's that huge gap on the radar on the west side where the circulation was closed from a radar view for quite a while.
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New Orleans outages

Link
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Latest vortex (and likely last by this recon) has a 968 mb storm...holding its own right now.
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Quoting tennisgirl08:


Thanks. I'm in Bama. Over 200 miles from the eye...but very scary tornado-like conditions here. Crazy!!



i have lucked out so far over here by halls mill & 90/193 :) stay safe especially if your over in the eastern shores area...oh and....

ROLL TIDE ROLL lol :)
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One last thing, over 310,000 people without power in Louisiana.
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About 310,000 power outages now being reported in Louisiana.
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Quoting Stormchaser121:
After 98L there is another storm showing up in the long range on the GFS coming off Africa and after that the GFS has 2 more waves rolling off Africa and 2 systems in the GOM forming off trough splits and tail ends of fronts.



are model runs really that good nowadays? to predict a storm over a month out....lol :)
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It's waaaay past time to go to sleep for me, good night everyone!
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Here around Mobile/Tillmans border we have received rain but no real severe winds....more like a large rainstorm to us here so far....I know it has been different across the bay, it's just the dry air pocket feeding in set up over the western shores for hours and hours here in Bama......

Isaac is the most tropical hybrid I have ever seen in my life....I am sure there are other storms similar, but to hit the north gulf coast at the end of august with this size, very cold winds and rain, and so much dry air.....Isaac is an oddball to say the least.....
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After 98L there is another storm showing up in the long range on the GFS coming off Africa and after that the GFS has 2 more waves rolling off Africa and 2 systems in the GOM forming off trough splits and tail ends of fronts.
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Quoting Felix2007:
Will Isaac be retired?
A) Yes
B) No


I think A for sure.
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it appears atleast a portion of the northren eyewall was moved inland now..offical second US landfall?
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report from fox 8 in new orleans of a barge breaking loose on the river and hitting 3 crew boats.... sinking 1... everyone allright though
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It appears dry air is starting to erode the NW quadrant of Isaac some.

Link

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Quoting tennisgirl08:


Thanks. I'm in Bama. Over 200 miles from the eye...but very scary tornado-like conditions here. Crazy!!

It sure sounds like it, one crazy hurricane!
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Quoting wxchaser97:

Stay safe then, got to be a sight to see.


Thanks. I'm in Bama. Over 200 miles from the eye...but very scary tornado-like conditions here. Crazy!!
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Quoting WaterWitch11:
:)


if you're less than 30 years old continue hollering
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EURO'S closest to SETX. Night everyone. Take care.

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thought i saw a bit of east drift the last few radar frames.......back to florida?, what a storm!.......lol
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Quoting Momnick8BR:
There's a group called Red Stick Storm Spotters on Facebook. They are the ones that reported 90% of Grand Isle under water but don't know where they got their info.


I did just see a video on TWC showing some part of Grand Isle underwater
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Quoting Elena85Vet:


Cloud tops have cooled, dry air entrained, eyewall likely collapsed. Sometime tomorrow (at best) for any 'flare back up'. He'll have to separate himeself from the coast as well.

It is Isaac though, he breaks all the rules.





......like a boss...lol
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Quoting Felix2007:
Will Isaac be retired?
A) Yes
B) No


NO
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There's a group called Red Stick Storm Spotters on Facebook. They are the ones that reported 90% of Grand Isle under water but don't know where they got their info.
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Gotta go to bed! 'Night!
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From about 8pm to now (2am), Isaac has moved a total of about 35 miles.
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Quoting AllStar17:


It could easily flare back up in short order.


Cloud tops have cooled, dry air entrained, eyewall likely collapsed. Sometime tomorrow (at best) for any 'flare back up'. He'll have to separate himeself from the coast as well.

It is Isaac though, he breaks all the rules.

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Good news, winds should be dropping, eye-wall is open!

Link
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Quoting Stormchaser121:
With that ridge building back again, im expecting a continue west or WSW movement


Maybe so. But the Bermuda High to his East is also backing off and weakening some.
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Quoting GTcooliebai:
Now I see who he takes after, that's Debby's brother.

LOL, this time the storm moves west. Don't forget Isaac is Ernesto's cousin;)
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Well I'm calling it in for a night, my prayers are out to the people in the path of Isaac as they are in for a long couple of nights.
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Quoting johnmc318:
Wasn't there a model a couple of days ago that stalled it out over south Louisiana.... I know that I didnt dream that



I believe the GFS showed a stall and a more westerly direction a couple of days ago...
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Quoting Slamguitar:
Looks like he's wobbling north again. Might not last. He needs to hurry up and spread the rain across the areas that really need it.

Isaac's movements have been very unpredictable. I hope we get some rainfall from Isaac.
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New Orleans current conditions:
ENE 44mph
gusting to 61 mph
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:)
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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.