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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Used to live in Mobile on Vanderbilt (across from USA) near Old Shell and Hillcrest, anybody around that area, curious what the conditions are?
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Quoting 1900hurricane:

Isaac killed the GFS!


Really moving southwest....
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Quoting 1900hurricane:

Isaac killed the GFS!


It couldn't figure out where the heck this thing was going, either, so it exploded.
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Quoting TampaFLUSA:
Crews clock 110 mph winds in Myrtle Grove. Lots of high voltage powering lines on LA 23 & drooping across it near energy sub station. #Isaac


How can these wind speeds be like this? hearing 100-120 is that possible in a 80mph hurricane?? Why is the nhc not reporting that?
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Quoting centex:
I think it closed off the dry air based on recent radar.


Yes, and a solid close it was.

That dry air pocket didn't accomplish much of anything.

Persistent storm here.
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THe latest IR image (4:30)either shows a dry slot or we may be seeing Isaac's eye beginning to clear. Compared to radar it may be the west edge of the eye.
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Quoting SomeRandomTexan:


I went to the one on hwy 69 in port arthur


Ah ok. My husband's been working at the one in Orange filling in. Usually works the Groves store.
Member Since: August 24, 2010 Posts: 0 Comments: 245
they keep saying landfall but it never actually does it
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Eye definitely looks to be contracting on radar. That would imply significant intensification is in process.
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Ok guys, it's offical. The name Isaac will be retired and never used again after this is all said and done!
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Quoting BrazoriaMan:
TWC explaining the west motion...very interesting. They are now expecting a westward motion to continue. They mentioned the model support. I wonder how far west Isaac will go.

Lets see ....at 8 miles an hour ....80 miles in 10 hrs
It could go in any direction .....
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658. txjac
Quoting 1900hurricane:
My roommate is doing some serious lurking at the moment. Y'all should convince him to post.


Hi roomie!
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It seems like the storm is taking a SSE movement on the New Orleans/Baton Rouge, LA radar from the NWS, so this storm is just wobbling around as it is stuck between the ridges.

This storm could just sit out there in the Gulf for another day before it heads towards land.

Nothing is directing it anywhere because its basically stuck, and I suppose its logical if it either just stalls or wobbles around places.
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Quoting BrazoriaMan:
TWC explaining the west motion...very interesting. They are now expecting a westward motion to continue. They mentioned the model support. I wonder how far west Isaac will go.


Well...if he crawls ever closer to Galveston then I might be looking more closely at the Mayan calendar or reaching for the Good Book...

Now THAT would be triple-eerie.

Reference to Isaac Cline, of course.


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I predict Its going to do a loop back into the gulf!
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Quoting RTSplayer:


It's not just you, they are talking about it on the weather channel.

The new specialist guy (forget his name) said about the same thing I did. The ridge on the west is jamming Isaac and causing it to stall out.


It's probably going to sit around raining for days until the next trough comes along...unless it gets pushed out to sea, and then we'll start this whole process over again....


The plains ridge is going to expand eastward eventually pushing Isaac westward under it. Then next trough will push him N, then NE. The trough will keep him from hitting TX.

He will linger where he is until the high builds...for at least a day.
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Latest few frames out of LIX are not even just SW.[..]

in nola
still with power
70119
991mb and falling
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Wondering when or if NWS will call for Tropical Storm warnings in Orange and Jefferson counties.
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Im out yall. Sleepy time. Be safe to all in the path.
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Mainly a lurker here with very little knowledge but i would like to point out two things:

1)TWC just talked about the scenario MLC gave about an hour ago. (stuck beneath NWesterly flow and moving west) Nice call MLC!

2) The reason the storm will not make it all the way to New Orleans? The dreaded and stout Jim Cantore shield, that guy cannot catch a break!

That is all, back to the shadows Stay safe all of you in harms way and congrats Patrap on the pups!
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Quoting sar2401:


Since it's apparently four hours late, I'd guess there are problems. :)

Isaac killed the GFS!
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The eye has moved 5 to 10mph to the SW in the past hour, based on using the "base velocity" tool on NEXRAD radar on wunderground and just watching the inflection points move SW.

The "calm" portion of the eye itself was right up to the land, and then it moved back off shore.
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Quoting floridaT:
he first tried to tract Ernesto, then tried to forecast isaacs strength. can ya blame him for drinking?


Well, no, you're right.

But I went with my answer not for that reason, but because I attended a couple of hurricane parties in Florida during my college years & got purty drunk. So kinda personal experience there.

P.S. Beginning my Masters next Spring, so it'll most likely happen at least once more. :( :(
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Quoting sar2401:


I don't think 911 would do much good, since the emergency service folks are hunkered down. What would you tell them if you did call? "A person on a blog, who I think was female, said she was going out to take pictures of Bayou St. John. No, I don't know her description, clothing, direction of travel, if she was in a vehicle..." etc. Highly unlikely they will take any action on a call like that on a night like this. Let's hope she's OK though.


The local radio people are still driving in and out at shift change and report NOPD and National Guard still on the streets. They said they were headed to Orleans Avenue at Bayou St. John, which is a pretty specific point, open land on three sides. I doubt they'd find anyone else out there jogging or walking the dog.

Glad they got home alright.

BTW, what happened to the guy from last year who was wearing some sort of home-made motocross armor who was going to strap himself to a lamppost or some such to get some video. He ever show up again?


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I think it closed off the dry air based on recent radar.
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Tennisgirl - get ready! looks like a some more heavy stuff getting ready to train over us again!
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Quoting GTcooliebai:
NOUS42 KWNO 290412
ADMNFD
SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE
NWS NCEP CENTRAL OPERATIONS COLLEGE PARK MD
0409Z WED AUG 29 2012
THE 00Z GFS WILL BE DELAYED DUE TO SYSTEM ISSUES ON THE NCEP
SUPERCOMPUTER...TECHS ARE LOOKING AT THE ISSUE AND UPDATES ON THE
TIMING OF 00Z PRODUCTS WILL FOLLOW AS NECESSARY...
OREILLY/SDM/NCO/NCEP


Since it's apparently four hours late, I'd guess there are problems. :)
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Quoting 1900hurricane:
Dry air looks like it may be trying to breach the western eyewall again.

That's what I thought too but that last frame it looks like Isaac might have close it off. Maybe..
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At least none of the models has it looping back around to the east, be like elena in 85, back and forth, that would drive folks insane
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Lived in Lake Chuck for 45 years, lost my house to Rita...Recently moved to Shreveport...in Lafayette for 2 weeks of training for my new job...at the Helliday Inn....got baloney and cheese.....If your post contains the letters TWC or the words "The Weather Channel", please refrain?
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Quoting sunlinepr:
The Worst of it???



way worse than that here
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Quoting 1900hurricane:

That's quite a large eye, larger than I expected it to be by a pretty large margin.


I'm losing track of time. Was it this morning or yesterday morning when the llc became really intense, symmetrical while the previously dominate and broad circ of the MLC had become more asymmetrical and less vertical?

The MLC had been dominate the whole trip, right up until near landfall. The smaller, somewhat linear LLC was having a heckuva time trying to spin up that larger circulation above. A bit more time out and that warm eddy spot and Isaac could have been a monster. Like it is, it's still gonna be deadly, but by stealth, guerilla-styled tactics.
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Back over water...Tx needs to watch it.
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Quoting tennisgirl08:


Love that place! The lower level of the FB is probably under water right now :(


Not their first rodeo. What's your take on this crazy storm? Stalled? This is the worst possible scenerio for New Orleans and surrounding areas. Just brutal.
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My roommate is doing some serious lurking at the moment. Y'all should convince him to post.
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Quoting AtHomeInTX:


Nah. If ya bought it in Orange they restocked it today. Apparently a lot of people are preparing. Like you said. It's a good idea anyway.


I went to the one on hwy 69 in port arthur
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Issac only pawn.. in game of life. (Mongo Blazing Saddles)

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The Worst of it???

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Quoting louisianaboy444:
Is it just me or is the center wobbling WSW?


It's not just you, they are talking about it on the weather channel.

The new specialist guy (forget his name) said about the same thing I did. The ridge on the west is jamming Isaac and causing it to stall out.


It's probably going to sit around raining for days until the next trough comes along...unless it gets pushed out to sea, and then we'll start this whole process over again....
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Quoting SomeRandomTexan:
I went to Wal-Mart tonight to get some water and batteries. They had a big stack of waters by the front door. I think we were the only ones buying any. Figured best have and and not need it than be wishing for it later.


Nah. If ya bought it in Orange they restocked it today. Apparently a lot of people are preparing. Like you said. It's a good idea anyway.
Member Since: August 24, 2010 Posts: 0 Comments: 245
Quoting louisianaboy444:
Is it just me or is the center wobbling WSW?


Not just you it is moving w/wsw/s. Turn on TWC they have been explaining it...
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Quoting tennisgirl08:
Heavy rain and gusty winds in Mobile now. These NE feeder bands aren't playing around anymore.



No doubt, same here on E Shore...Could be much worse, of course. NOLA gonna be getting it much worse. Lots of transformers popping there. Nothing like that here, but then again, I am not in an urban area. As in, I worry about 1 transformer!!
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Quoting 1900hurricane:
Latest infrared:



Is not creating convection.........When the D-max comes
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it took isaac 10 hours to go 100 miles... now in 45 mins he looks to be 100 miles back offshore
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I am not sure if you can determine anything specific from this storm right now, but in my perspective it appears to be headig back towards the southwest and into the GOF.
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Isaac is a very weird Storm !!!
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Link

House in Bay St Louis MS Burns down amid flooding
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TWC explaining the west motion...very interesting. They are now expecting a westward motion to continue. They mentioned the model support. I wonder how far west Isaac will go.
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RT @28storms: RT @ScottGordonNBC5: Mayor of Grand Isle, LA: "If this is a cat 1, I don't want to see a cat 3." Island cut off. #Isaac
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Dry air looks like it may be trying to breach the western eyewall again.
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looks like dry air may be trying to work its way into the center as well. imo
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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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