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 AussieStorm:

Are you able to give me a link to TWC?



here Link
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Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting lopaka001:
Is the eye looking better now? Been drinking not sure if I should stop or continue.



Yes (looks better)

Last vortex said it was ragged, but everything else indicated it's a good eyewall
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Isaac's eye is getting the most symmetrical it has ever been. Almost perfectly round at the moment. Sure seems to be still organizing.
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I am betting that Isaac is doing another loop-de-loop.
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Buoy 42012 was reporting wave heights of near 20 ft.
Near Orange Beach, Alabama.
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Quoting JeffM:


Ditto


I had no issues with the TWC, are you talking about a internet link or something? I got Directv and it looks fine with no issues other then them cutting off their reporters from time to time.
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Quoting runnomore:


Well guess that makes three I am in Pearland also.


Good eveing fellow Pearlanders. Wal Mart run anyone? We may need it! Dixie Farm one tho! Silverlake is tooo busy!
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the eye has perfect symmetry in that last frame.
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Symmetry of the eye has improved in the past few frames, although there is some dry air trying to attack it on the left eye wall.

It still looks to be moving south, ironically.
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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
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Issac doesn't look to have many outs.
Link
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TWC back here
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make that 4 in Pearland...so am I...back to lurking.
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Quoting floridaT:
is he working with stephany?


not now !
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Is the eye looking better now? Been drinking not sure if I should stop or continue.

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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.
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Quoting GTcooliebai:
I don't blame them they have more things to worry about right now, making sure everyone in their household is safe, and that they haven't sustained any damage.

Niether do I, even though Isaac is "only a cat1" he is still dangerous.
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Quoting zillaTX:


Glad you are no longer in a panic over Helene ;p

Yea u can say that lol!
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ARW has landfall 33 hours past its 21Z initialization around Vermillion Bay. Seems like as good a forecast as any to me, especially since it appears that the ARW is preforming quite well with Isaac.

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Quoting GTcooliebai:
How are the winds like, looks like a strong band moved through not too long ago?



very strong band came through about 20 min ago when I was outside

another one primed to come through. Oddly still have power.

wunderground radar out of lix has slight movement SW but thats only in the last 30 min of frames.
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Quoting WeatherfanPR:
OMG !!! I'm watching the live broadcast of TWC on internet and I just heard Al Roker changing the name of Hurricane Isaac twice in the same report. First he referred Isaac as Hurricane Ike and then as Hurricane Irene. I think Al Roker is not ok.

Are you able to give me a link to TWC?
Member Since: September 30, 2007 Posts: 9 Comments: 15961
E. Shore, Mobile Bay, Alabama:

Pretty strong rain / wind minutes ago, relative to what we have had earlier today / this evening.

I'd say we have had 2-3 inches in the last 90 minutes...? Wind not that bad but for a few gusts, similar to a strong thunderstorm. But definitely stronger than anything up to this point.

Looks like we will be training this band for the next 6-7 hours.

Nothing like the LA folks though. Ugh. They have > 24 hours of rain in front of them.
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Local Fox Station in New Orleans streaming

Link
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Still a Green screen at 12:18am EST in Orlando on TWC!
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Quoting iahishome:
Isaac looks set to cross very near Katrina's original landfall point. It would be neat, and kind of spooky to see those side by side.

Should be pretty close to exactly 7 years apart too, ya think?



29.1 N... 89.6 W - Katrina landfall in Louisiana....

29.0 N... 89.4W - Isaac landfall
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Quoting wxchaser97:

Wxh98 said in chat earlier that he was losing power and wouldn't be around for a while.
EDIT: TWC is back up.
I don't blame them they have more things to worry about right now, making sure everyone in their household is safe, and that they haven't sustained any damage.
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Quoting BrazoriaMan:


I see. So the high is building in towards the west, pushing Isaac that way. And I am assuming the high in the plains is kind of blocking Isaac as well. Could this thing really be headed for the TX/LA border like some of the models suggested days ago? It's amazing how fast weather changes! Thanks!


We got our worst winds and rains from Isaac when he was nearly 400 miles away, I wouldn't discount anything. Right now Louisiana & Miss are getting hammered.
Member Since: August 19, 2005 Posts: 5 Comments: 5452

This storm seems to be heading SSW currently as of now, this is surely one weird system.
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540. JeffM
Quoting Elena85Vet:
No Weather Channel audio or video in Omaha, NE.

Last 15 minutes have been a green screen with just the local conditions at the bottom.

No audio either


Ditto
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Quoting AtHomeInTX:


Bet there's mosquitoes aplenty. Lol.


Any ants or animals acting strange over there?
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Quoting AtHomeInTX:


Morning Trauma. How's things your way? :)


Morning AtHome!!

Glad to be sitting this one out!! Two days ago they had it running over my house....At least gave us the chance to knock the dirt dobblers out of the generators and I got three hundred gallons of water ready to go.....all we got wuz beautiful weather and a break from the rain!! Besides the skeeters...how are things in Texas??
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Check the Bourbon Cam.... small crowd and a police car.... there...

Link
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Quoting WeatherfanPR:
OMG !!! I'm watching the live broadcast of TWC on internet and I just heard Al Roker changing the name of Hurricane Isaac twice in the same report. First he referred Isaac as Hurricane Ike and then as Hurricane Irene. I think Al Roker is not ok.
is he working with stephany?
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Quoting WeatherfanPR:
OMG !!! I'm watching the live broadcast of TWC on internet and I just heard Al Roker changing the name of Hurricane Isaac twice in the same report. First he referred Isaac as Hurricane Ike and then as Hurricane Irene. I think Al Roker is not ok.


he's been standing out there being pummeled for no good reason for a long, long time.
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Doubt this makes landfall for quite sometime looking at its current motion
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Quoting AtHomeInTX:


Bet there's mosquitoes aplenty. Lol.
Plenty in Houston. Couldn't find any unusual ant activity today.Forecast good
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No Weather Channel audio or video in Omaha, NE.

Last 15 minutes have been a green screen with just the local conditions at the bottom.

No audio either
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TWC is working again, really don't know what caused that.
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Quoting TampaFLUSA:

Yes it also occurred to me to report what's happening now and not drooling over every wobble and hoping its coming ny way.
Well, keep reporting! We're listening.
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Quoting DavidHOUTX:
@twc_hurricane

Latest NOAA recon plane found a min. central pressure of 966mb inside #Isaac at 10:35pm CDT, the lowest pressure yet.


This is bad.

The western ridge is stronger than the eastern.

The stome may be moving back out to sea, and intensifying all the while...

It certainly looks to be moving SW on some radar loops.
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Quoting GeauxGirl:


I know, right? Hackers? LOL...

IT'S BACK!!


still green screen TWC in Raleigh
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Quoting floridaT:
no sheets sherlock

Priceless......
The one night it's Happening.....black out
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OMG !!! I'm watching the live broadcast of TWC on internet and I just heard Al Roker changing the name of Hurricane Isaac twice in the same report. First he referred Isaac as Hurricane Ike and then as Hurricane Irene. I think Al Roker is not ok.
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Quoting Diabellical:


power still up here.

midcity. 70119
How are the winds like, looks like a strong band moved through not too long ago?

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Quoting traumaboyy:
Good morning Night shift!! Coffee is ready!!

Enjoying reading where everyone thinks this thing might be heading.....And moonlightcowboy is bringing back memories of Elana(sp?) that skirted back and forth along the northern GOMEX back in 84 or 85. Anybody hearing anything from NOLA?? At work so can't watch the Boob Tube for updates!!


Morning Trauma. How's things your way? :)
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Quoting wxchaser97:

Wxh98 said in chat earlier that he was losing power and wouldn't be around for a while.
EDIT: TWC is back up.

Also GetReal as well
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I wonder if Isaac gets underneath the Texas ridge and decides to move WSW toward the Texas coast. This would just prolong this journey and even give him some room to strengthen. I believe back in 1977 a hurricane named Anita did something similar. Correct me if i am wrong. Anyone think this could be possible?
Member Since: September 9, 2011 Posts: 0 Comments: 439
Quoting terry107:


Small world - I'm in Pearland as well.

Back to lurking.


Well guess that makes three I am in Pearland also.
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Quoting Skyepony:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 29th day of the month at 04:06Z
Corrected: This observation corrected a previous observation.
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 308)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 32
Observation Number: 14
A. Time of Center Fix: 29th day of the month at 3:40:50Z
B. Center Fix Coordinates: 2900'N 8955'W (29.N 89.9167W)
B. Center Fix Location: 68 miles (109 km) to the S (173) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,161m (3,809ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 54kts (~ 62.1mph)
E. Location of the Estimated Maximum Surface Wind: 60 nautical miles (69 statute miles) to the SE (132) of center fix
F. Maximum Flight Level Wind Inbound: From 224 at 72kts (From the SW at ~ 82.9mph)
G. Location of Maximum Flight Level Wind Inbound: 65 nautical miles (75 statute miles) to the SE (132) of center fix
H. Minimum Sea Level Pressure: 968mb (28.59 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17C (63F) at a pressure alt. of 1,529m (5,016ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22C (72F) at a pressure alt. of 1,520m (4,987ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 22C (72F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character (Undecoded): RAGGED
M. Eye Shape & Diameter: Circular with a diameter of 40 nautical miles (46 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 2 nautical miles
Remarks Section:
Maximum Flight Level Wind: 86kts (~ 99.0mph) in the northeast quadrant at 1:49:30Z
Maximum Flight Level Wind Outbound: 82kts (~ 94.4mph) in the southwest quadrant at 3:51:30Z

That's quite a large eye, larger than I expected it to be by a pretty large margin.
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TWC working here, but with static.
Member Since: August 22, 2009 Posts: 0 Comments: 3159

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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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