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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TWC working here, but with static.
Member Since: August 22, 2009 Posts: 0 Comments: 3125
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!

I think it can happen.
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Quoting wxchaser97:
Is anyone having a problem with TWC?


Yes, went black on my end.
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Quoting AllBoardedUp:
Did it ever occur to you that people in New Orleans have bigger fish to fry than be on a weather site in the middle of a hurricane. That's if they even have power.

Yes it also occurred to me to report what's happening now and not drooling over every wobble and hoping its coming ny way.
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Quoting RTSplayer:
I don't know if TWC knows this, but they've lost both video and audio.

The only thing they are transmitting is their warning text ticker at the bottom of the screen.
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Quoting GTcooliebai:
Looks like our friends in NOLA have lost power. Patrap, RTS, and weather98.


Outage map
Link
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Quoting Ryuujin:


Back out to sea AGAIN?


It was a day early... it appears to be waiting for the anniversary date :(
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looks to be headed south on the radar
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511. JeffM
Isaac (or Al Roker) took down TWC.
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Quoting JeffM:


Maybe rain bands isn't the word I'm looking for. The blue area is close to Houston.


High clouds? lol!
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Quoting KEEPEROFTHEGATE:

Definitely sagging to the SW. In the short term, it looks like the ARW has a great handle on Isaac.
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Quoting wxchaser97:
Is anyone having a problem with TWC?



You're not the only one.. out in DFW - U-verse
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Quoting AllBoardedUp:
Did it ever occur to you that people in New Orleans have bigger fish to fry than be on a weather site in the middle of a hurricane. That's if they even have power.



Also the people in NOLA cant prepare for it anymore because its already there the people in SE texas can prepare and should prepare now for it just in case it does head their way
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Quoting AllStar17:
Worst possible time for The Weather Channel to stop working.


I know, right? Hackers? LOL...

IT'S BACK!!
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Quoting JeffM:


Maybe rain bands isn't the word I'm looking for. The blue area is close to Houston.

not rain. closest rain is off shore east of Morgan City
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TWC back online made me jump.
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Quoting HoustonTxGal:


Issac is on rails! someone de-rail him!


The rails run right through Pearland lol. Yikes! I wouldnt mind some rain thats for sure. I know North Houston got gobs of rain not too long ago, but many people still need it around here. While storms are amazing to watch and be in, I am not in the mood for no power for two weeks.
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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.



LOL
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Quoting GTcooliebai:
Looks like our friends in NOLA have lost power. Patrap, RTS, and weather98.

Wxh98 said in chat earlier that he was losing power and wouldn't be around for a while.
EDIT: TWC is back up.
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Quoting nolacane2009:
i have a bad feeling that one of my outer walls might collaps. everytime a strong gust of wind it pushes in and out.


That must be scary...any idea what speed the gusts are??
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Quoting AtHomeInTX:


Bet there's mosquitoes aplenty. Lol.


And they carry switch blade knives!
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Huummm .... In about 2 minutes, BAM ... 4-5 cop-cars, 1 HUMMV, & 5 or 6 cops & soldiers on foot blocked this Bourbon Street webcam, questioning 1 guy in a tank-top for a minute or so. Then what looked like a black hearse with red lights on weaved through the intersection.

Wonder what dat were 'bout?
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Quoting GTcooliebai:
Looks like our friends in NOLA have lost power. Patrap, RTS, and weather98.


power still up here.

midcity. 70119
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Quoting TampaFLUSA:
Here's is a actual report from N.O. since Texas people have hijacked this blog.
New Orleans lakefront just reported a gust of 71 mph at 10:27pm CDT. #Isaac
Did it ever occur to you that people in New Orleans have bigger fish to fry than be on a weather site in the middle of a hurricane. That's if they even have power.
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Quoting STXHurricanes2012:
Evening all,I see our friendly friends from southeast tx still say its heading in that direction.It is but it'll be inland and probably more weaker than it is now! So just expect rain out of it. Winds won't be that bad! Lol silly guys!!


Glad you are no longer in a panic over Helene ;p
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Quoting nolacane2009:
i have a bad feeling that one of my outer walls might collaps. everytime a strong gust of wind it pushes in and out.


That sounds very bad. Seek a safe location.
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Quoting Jwd41190:
Weather channel not working....
no sheets sherlock
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Looks like our friends in NOLA have lost power. Patrap, RTS, and weather98.
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Quoting BmtJedi:


That's true, but that was at 10:00 PM CST, an hour ago. Although, there have been hints it is happening again.
Quoting TexasHurricane:


What does that mean?


Poster was asking why it could be moving west right now. I was giving my thoughts. The AB high being flattened means it is pressing on Isaac and with the US ridge built overhead currently Isaac has nowhere to go except west or erratic motion. Kind of like a squeeze play.
Member Since: August 19, 2005 Posts: 5 Comments: 5401
Quoting txlamomma:
Nope..no rain bands or wind..dead. calm..not even cricket or frog sounds tonight..so far..sabine river here


Bet there's mosquitoes aplenty. Lol.
Member Since: August 24, 2010 Posts: 0 Comments: 151
488. FOREX
Quoting wxchaser97:
Is anyone having a problem with TWC?



yuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuup
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I don't know if TWC knows this, but they've lost both video and audio.

The only thing they are transmitting is their warning text ticker at the bottom of the screen.
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Quoting KEEPEROFTHEGATE:


Back out to sea AGAIN?
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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?
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im sorry i just dont see a stable nw motion at 8 mph
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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.


it's the idea and the care for a human life. Not the act.
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Quoting moonlightcowboy:




Thanks for your posts. There's little explanation coming from the NHC and the previous forecasts seem to be OBE (overtaken by events).
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481. FOREX
Quoting GTcooliebai:
Ok I thought it was my TV.


WTC off air in FL panhandle
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480. Skyepony (Mod)
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: 29°00'N 89°55'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: 17°C (63°F) at a pressure alt. of 1,529m (5,016ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,520m (4,987ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 22°C (72°F)
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
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Quoting GTcooliebai:
Ok I thought it was my TV.


I will never forget a day/day and a half before Isaac hit two channels went out on cable..yes only two, out of hundreds. Some crap channel, and the Weather Channel. I called Comcast Cable(Houston), and said " What is wrong with TWC?" She replies..."We have an outage." Out of the two channels in the world to be out, TWC is OUT??? We are about to have a hurricane. Not too long after we switched providers lol.
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Is anyone having a problem with TWC?
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Member Since: July 15, 2006 Posts: 171 Comments: 53838
@twc_hurricane

Latest NOAA recon plane found a min. central pressure of 966mb inside #Isaac at 10:35pm CDT, the lowest pressure yet.
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Here's is a actual report from N.O. since Texas people have hijacked this blog.
New Orleans lakefront just reported a gust of 71 mph at 10:27pm CDT. #Isaac
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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!!
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Quoting WetBankGuy:
Anyone seen a post from the person saying they were going out to take a picture from Bayou St. John? If you're still on the board text me 504 579 9672 or I'm thinking of calling 9-1-1. There was a tremendous gust just after she posted that message.



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.
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Quoting nolacane2009:
i have a bad feeling that one of my outer walls might collaps. everytime a strong gust of wind it pushes in and out.


Good grief...get to an inside room with no windows....inside load bearing walls are stronger...be safe!!!
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Worst possible time for The Weather Channel to stop working.
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Quoting JeffM:
11:00 PM CDT Tue Aug 28
Location: 29.1°N 89.9°W
Moving: NW at 8 mph
Min pressure: 968 mb
Max sustained: 80 mph


This thing is a fighter!
It's still offshore and I thought upwelling would get to it, but forgot the water is pretty shallow over there and it is moving, well I should say crawling. Looks like the Central Plains Ridge has taken over the steering for the time being.
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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!


Issac is on rails! someone de-rail him!
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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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