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 TexasHurricane:
Channel 12 - SETX

"The next 12 hours will be crucial in the forecast for Southeast Texas. The storm is forecasted to gradually turn towards the northwest and then north. If it does not turn, or that turn is later than forecasted, then tropical storm force winds (or worse) could occur in Southeast Texas by Late Wednesday Night. The latest radar imagery actually shows a southwest movement the last hour or so. It is unclear if this is temporary.:


WOW figured they were asleep!! LOL
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Quoting Jay5711:


U telling me.. Local met said we should start to see the "bad weather" later on tomorrow afternoon... At the speed it was moving earilier today I'd figured it would pass through tonite..

Isaac is just battering Louisiana and wont stop for a couple days, stay safe. Been good to see a lot of new people join over the past week due to Isaac.
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Quoting Bielle:
I've had to be AFK for several hours: did Patrap's puppies arrive safely?


2 pups so far..one male..one female!!
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Channel 12 - SETX

"The next 12 hours will be crucial in the forecast for Southeast Texas. The storm is forecasted to gradually turn towards the northwest and then north. If it does not turn, or that turn is later than forecasted, then tropical storm force winds (or worse) could occur in Southeast Texas by Late Wednesday Night. The latest radar imagery actually shows a southwest movement the last hour or so. It is unclear if this is temporary.:
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AI am in Terrytown and lost power. Y'all are my source of info now. What does it look like for my area. I am South of New Orleans on the westbank. Getting very scary with the winds howling.
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I've had to be AFK for several hours: did Patrap's puppies arrive safely?
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Quoting StormDrain:
sara, The storm doesn't appear to be moving much at the moment. The winds and rain will circle around the center and dump a lot of rain until it moves off and then inland. Even then there will be more wind and rain. As far as the eye reforming. Isaac has a big ragged eye that's looking a little more ragged. Probably not strengthening right now but will continue to bring wind and rain. Do you know how to put Mandeville into the wu radar and watch for strong rain bands and cells coming your way?
no i don't and i want to thank you for answering my questions. i have 2 girls and i am getting a bit nrevous. so thanks! :)
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Quoting CCkid00:

do you think it will go back to tracking northwest?
The average, long term motion tonight has been WNW or NW and Isaac will continue in that direction as mid level steering points him in that direction. The short term erratic movements we've seen tonight (loops, jogs, wobbles, trochoidal oscillations, etc) are due to the fact that steering, although NW/WNW, is very weak. As a result, Isaac has been moved around by the irregular friction from the Mississippi river delta and the uneven spread of the convective mass around the eye.
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Quoting stormchaser19:
He wants to come again in september OH boy!!!!!!!

That could help take care of some of the stable sinking air. September doesn't look to be quiet as signs point for more storms.
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Quoting sarahjola:
wow! not one person can take on these questions? thanks again for a major fail on what used to be a very useful, and educating weather blog.

Someone did respond to your post...
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Quoting sarahjola:
bet i get an answer to the "thanks for a major fail" comment, but nothing on the weather comments.


I think you missed the answers...someone told you the eye is not reforming rather looking more ragged due to warming cloud tops, land interaction and being over shallow water...it looks as if the storm has peaked for the moment...
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Quoting xtremeweathertracker:


LOL....4 of the 6 bring Isaac into eastern TX and through northeast Texas!!


I think Levi explained earlier to your post as well. "A liittle bit of rain, no big deal."

Mostly will affect ARK.
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Quoting zillaTX:


Eh???


The NHC masy not show this in the next statement, but he is falling apart. I had prior thought he may have been recurving back to the GOM, but latest info has proved me otherwise and has hence showed he is falling apart slowly...IMO.
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bet i get an answer to the "thanks for a major fail" comment, but nothing on the weather comments.
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Td 12 looks to be coming tomorrow or after tomorrow.
Atlantic Tropical Weather Outlook


000
ABNT20 KNHC 290538
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT WED AUG 29 2012

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
ISAAC...LOCATED NEAR THE COAST OF SOUTHEASTERN LOUISIANA AND ON
RECENTLY UPGRADED TROPICAL STORM KIRK...LOCATED ABOUT 1440 MILES
SOUTHWEST OF THE AZORES.

A BROAD LOW PRESSURE AREA ASSOCIATED WITH A TROPICAL WAVE IS LOCATED
ABOUT 550 MILES WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS. THE
ASSOCIATED SHOWER ACTIVITY IS GRADUALLY BECOMING BETTER
ORGANIZED...AND ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE
CONDUCIVE FOR SLOW DEVELOPMENT DURING THE NEXT COUPLE OF DAYS. THIS
SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD AT ABOUT 15
MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
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Quoting wxchaser97:
Thanks, going to be a long two days for Louisiana. I'm surprised I was able to do it since I'm really tired.


U telling me.. Local met said we should start to see the "bad weather" later on tomorrow afternoon... At the speed it was moving earilier today I'd figured it would pass through tonite..
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wow! not one person can take on these questions? thanks again for a major fail on what used to be a very useful, and educating weather blog.
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He wants to come again in september OH boy!!!!!!!
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Quoting NOWORRIES:
Isaac is no longer a hurricane.

Ah no, Isaac is still a hurricane.
...ISAAC MOVING SLOWLY ALONG THE COAST OF SOUTHEAST LOUISIANA AND PRODUCING A DANGEROUS STORM SURGE...FLOODING FROM RAINFALL ALSO EXPECTED... ...U.S. Warnings in Effect...
12:00 AM CDT Wed Aug 29
Location: 29.0°N 90.0°W
Moving: WNW at 7 mph
Min pressure: 969 mb
Max sustained: 80 mph
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Quoting TomTaylor:
Didn't realize we had another vortex message already, but here are the last 11 from the NOAA and USAF planes. Intensification was evident earlier this evening, however pressures have risen over the last two hours.

Time - Pressure - Flt.Lvl - Sfc.Lvl - Plane

04:34 969 86 59 USAF
03:40 968 86 54 USAF
02:35 966 81 61 NOAA
01:45 971* 91 59 NOAA
01:26 968 96 61 USAF
00:42 967 91 -- NOAA
23:57 968 96 57 USAF
23:44 970* 91 62 NOAA
22:44 971 91 -- NOAA
22:25 970 94 61 USAF
21:59 971 80 -- NOAA

* = extrapolated value

Also cloud tops have warmed some, Isaac looks to have leveled off intensity wise.
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Quoting NOWORRIES:
Isaac is no longer a hurricane.


Eh???
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847. etxwx
Quoting Levi32:


Most reliable models keep the center over Arkansas. Extreme east Texas could get a little rain but no big deal.

As someone in extreme East Texas, I'm gonna hold you to that, Levi. ;-)
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i wouldn,t be surprised to see him ride up the eastern side of TX
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Quoting sarahjola:
this too. i'm in mandeville and starting to get a bit worried about this insane storm that just won't make up its mind. tia!
sara, The storm doesn't appear to be moving much at the moment. The winds and rain will circle around the center and dump a lot of rain until it moves off and then inland. Even then there will be more wind and rain. As far as the eye reforming. Isaac has a big ragged eye that's looking a little more ragged. Probably not strengthening right now but will continue to bring wind and rain. Do you know how to put Mandeville into the wu radar and watch for strong rain bands and cells coming your way?
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Quoting WetBankGuy:


Hungry? Have a derecho. There's some bean dip over there. Went through two of those mini-canes (wind wise) in NW Minnesota, and remember the one that flattened the Boundary Waters like the Tunguska. The Detroit Lakes, MN one did Cat 2 damage (large limbs and trees down, roofs and chimneys damaged. power out almost 3 days.}

No thanks, dont need any damage. Could use some rain but no wind please:)
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Quoting thesweetlycool:



Me too. In Grand Rapids

Cool, I'm in Metro Detroit. Hopefully we can get some of Isaac's remnants up here.
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this hurricane is soooooooo slow. denham springs, la. here, about 10 miles east of BR. winds picked up at daylight this morning (well, actually Tuesday morning). they have been probably 25-30 all evening and night, with gusts to 35. just a sprinkle of rain earlier. strange storm.
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Kirk's a bit a tropical quirk. The guy's trying to steal the spotlight from Isaac, and it's working enough so that Isaac can no longer see where e is going and is bumping into stuff and wobbling around. Give it back, Kirk! He needs it!
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Quoting AtHomeInTX:


I agree with your Isaac track. My brain can't get started on the other one yet. :) Anyway, I've been calling for a Gustav track for days. Lol. If I'm wrong I'll eat my first crow.
Thanks, going to be a long two days for Louisiana. I'm surprised I was able to do it since I'm really tired.
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Isaac is no longer a hurricane.
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Quoting allancalderini:
May be up to 50 or 60 at the next advisory imagine if he strength into a hurricane so much for rip.LOL XD.

He has a chance of attaining hurricane status, these storms have been doing that at these latitudes this year.
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After boring July active August MJO have a big part in this august activity
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Hi from sw Louisiana. Not a drop of rain so far..... Light winds, gusts maybe 35 mph. Keeping an eye on that nasty fellow in the gulf.
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Quoting tennisgirl08:


Look at the latest models on wunderground site for midnight, Aug. 29th. Supposed to make second landfall in Central LA, move NW, N, then NE recurve.

I don't see much of TX in there....sorry. The plains high will be too strong.


LOL....4 of the 6 bring Isaac into eastern TX and through northeast Texas!!
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Looks like Isaac may be drifting to the NW again, but extremely slowly.
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I'll get to responses in a minute as I'm busy with an Isaac update.
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Quoting AtHomeInTX:


I'm hangin'. And sleepy. :)



awwwwwwwwwwwwwww i know you are
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Quoting xtremeweathertracker:


Hey Levi what are your thoughts on the latest westward wobbles or trend...do you think the latest model guidance is valid in bringing Isaac wnw into parts of Tx?


Look at the latest models on wunderground site for midnight, Aug. 29th. Supposed to make second landfall in Central LA, move NW, N, then NE recurve.

I don't see much of TX in there....sorry. The plains high will be too strong.
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Quoting xtremeweathertracker:


Hey Levi what are your thoughts on the latest westward wobbles or trend...do you think the latest model guidance is valid in bringing Isaac wnw into parts of Tx?


Most reliable models keep the center over Arkansas. Extreme east Texas could get a little rain but no big deal.
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Quoting Levi32:


More likely starting to collapse a bit given warming cloud tops in the eyewall and likely cooler SSTs beneath it now due to evaporation.


That makes sense. And its over some relatively shallow water (oh mama) so not a lot of energy there. Weak and West is all the fashion here in New Orleans tonight.

Winds seemed to have died down substantially in town. Lots of gusts but not the same sustained winds we had an hour ago. MSY reporting 38 mph.
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Didn't realize we had another vortex message already, but here are the last 11 from the NOAA and USAF planes. Intensification was evident earlier this evening, however pressures have risen over the last two hours.

Time - Pressure - Flt.Lvl - Sfc.Lvl - Plane

04:34 969 86 59 USAF
03:40 968 86 54 USAF
02:35 966 81 61 NOAA
01:45 971* 91 59 NOAA
01:26 968 96 61 USAF
00:42 967 91 -- NOAA
23:57 968 96 57 USAF
23:44 970* 91 62 NOAA
22:44 971 91 -- NOAA
22:25 970 94 61 USAF
21:59 971 80 -- NOAA

* = extrapolated value
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looking for a little help understanding what we may be looking at. can anyone answer this or is this storm just too confusing for anyone to even try to elaborate on what norwood is saying?
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Quoting will40:


hang in there girl


I'm hangin'. And sleepy. :)
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Midcity New Orleans here:

I suspect we wont have power for much longer.

Looks like the squalls incoming may have some rotation.

Talk to you guys in the AM
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70% Westbank without power....

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823. tessa
For those of you in SE Texas, these are some warninings I saw on the Weather Channel and sent to my son who is in between Houston and Beaumont..."Sabine Pass, Tx has now been put under Tropical Storm Warning. From Sabine Pass to Mogan City, La. Tropical Storm Watch is now in effect east of High Island, Tx to just west of Sabine Pass, Tx." I sent these to him at 10 pm tonight. Tessa
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First official hurricane-force gust in New Orleans - Lakefront Airport gusted 76 mph at 12:07am CDT. #Isaac
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Quoting wxchaser97:

That would be interesting as I'm in Michigan.


Hungry? Have a derecho. There's some bean dip over there. Went through two of those mini-canes (wind wise) in NW Minnesota, and remember the one that flattened the Boundary Waters like the Tunguska. The Detroit Lakes, MN one did Cat 2 damage (large limbs and trees down, roofs and chimneys damaged. power out almost 3 days.}
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Quoting sarahjola:
nacondra norwood said eye reforming. what can this mean for new orleans and st. tammany parish? tia!
this too. i'm in mandeville and starting to get a bit worried about this insane storm that just won't make up its mind. tia!
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Quoting allancalderini:
Have you receive rain athome?


Nope not a drop. Beautiful day today. :)
Member Since: August 24, 2010 Posts: 0 Comments: 58

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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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