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 HoustonTxGal:


Careful, you will get accused of wishcasting.

Yeah. Even though its the truth.
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Quoting RTSplayer:


I don't doubt it based on the pressure and the newly formed eye wall...

Earlier, this cell was moving 86kts or about 99mph. Right now it has slowed to "only" 72knots, which is still 83mph.


G7 43 dBZ 7,000 ft. 2 kg/m² 0% chance 0% chance 0.00 in. 72 knots ESE (108)


Did you see cell E4 @ 10:27 pm? 93 knots / 106 mph
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Power is now out for good.

See y'all later.

I'll try to get TAWX 13 to upload images for me.

Goodnight.
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Quoting HurricaneHunterJoe:


Just reporting what I saw on T.V. Jefferson Parish President said the mayor of Grand Isle said gusts at 120mph.


I know, just trying to figure that out. That would imply either his instrument, or the NHC are in error.
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Quoting Patrap:


Looks due west to me for the last 1.5hrs....... be interesting to see how long this continues!!!!
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Possible quasi-EWRC going on?
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Quoting HurricaneHunterJoe:


Just reporting what I saw on T.V. Jefferson Parish President said the mayor of Grand Isle said gusts at 120mph.


He is a wind-wish-caster
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Grand Isle,LA getting the eye right now...
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Quoting TreasureCoastFl:
Hey you were right on with that eye in the eye thing!


Thanks. I seen it much earlier just didn't know that was the actual center they were tracking. I thought it was an embedded vort and not an actual center as detailed by Dr. Masters. It was quickly absorbed after landfall IMO.

This is an image when I started watching.

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Mayor of Grand Isle just said on WWLTV that they had a wind gust up to 120 mph. Can this be accurate?
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Quoting aislinnpaps:
LOL, I can just see the pups with Pat and Nola Roux,
Isaac
Lil Miss Fresca
Roker
Cantore
Jeff
Stephanie
Bryan
Mudfall
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Quoting Patrap:
Nola Roux with first two..


Adorably ugly! Which is as it should be considering the storm they were born under.
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Quoting Patrap:
Nola Roux with first two..


Beautiful!
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Quoting kidd5433:


That's not Hi-Def!!!! Can't watch my Hurricane coverage in Low-Def


In the words of the legendary Chris Farley:
"La-tee-frickin-dah!"
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Quoting HrDelta:


Well, something ain't right. That means either the instrument has gone bad, or somebody is underestimating the storm. Would gusts of that speed indicate higher sustained?


Just reporting what I saw on T.V. Jefferson Parish President said the mayor of Grand Isle said gusts at 120mph.
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i dont recall i said wishcaster

I said yall got maps and isaac has a middle finger.

the nam is like pulling out the xtrp and telling me where its going.

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LOL, I can just see the pups with Pat and Nola Roux,
Isaac
Lil Miss Fresca
Roker
Cantore
Jeff
Stephanie
Bryan
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David Camerdelle reporting winds of 100-120 mph. in gusts.
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Quoting weatherh98:
every time theres a jog west the texans pull out those fancy maps

isaac pulls out his muddle finger and goes north
What, are you afraid someone is going to steal your thunder? Pardon the pun.
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Quoting NeverPanic:


Wilma if memory serves me correct.
http://www.ncdc.noaa.gov/special-reports/wilma.ht ml


No, Wilma was a Cat 5 that made landfall in FL as a Cat 3.

Lowest Atlantic storm pressure of 882 mb.
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Quoting floridaT:
it amazases me. i lived on marco when wilma came, they had the strictest building codes from the beginning. wilma direct hit lotta pool cages gone but that was the bulk of the damage. but we still had power lines not buried.


To be fair, with how high the water table is in Florida, it may be a bit of a pain/expensive to bury the lines.
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Now anytime I hear that a storm is a slow mover I think of Frances. She was hell!
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Product: NOAA Vortex Message (URNT12 KWBC)
Transmitted: 29th day of the month at 00:12Z
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 33
Observation Number: 26
A. Time of Center Fix: 28th day of the month at 23:44:36Z
B. Center Fix Coordinates: 29°02'N 89°25'W (29.0333N 89.4167W)
B. Center Fix Location: 76 miles (122 km) to the SSE (149°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 2,898m (9,508ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 62kts> (~ 71.3mph)
E. Location of the Estimated Maximum Surface Wind: 53 nautical miles (61 statute miles) to the SSW/SW (214°) of center fix
F. Maximum Flight Level Wind Inbound: From 333° at 66kts (From the NNW at ~ 76.0mph)
G. Location of Maximum Flight Level Wind Inbound: 57 nautical miles (66 statute miles) to the SW (215°) of center fix
H. Minimum Sea Level Pressure: 970mb (28.64 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 12°C (54°F) at a pressure alt. of 3,062m (10,046ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 3,048m (10,000ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 13°C (55°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Poorly Defined
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 700mb
O. Fix Determined By / Fix Level (Undecoded): 1 / 1 nm
Remarks Section:
Maximum Flight Level Wind: 91kts (~ 104.7mph) in the northeast quadrant at 22:10:20Z
Maximum Flight Level Wind Outbound: 79kts (~ 90.9mph) in the northeast quadrant at 23:56:14Z
Sea Level Pressure Extrapolation From: 700mb
Member Since: August 18, 2009 Posts: 0 Comments: 460
Hurricane Isaac
Last Update: 8/28/2012 10:00 PM
Position:29, -89.7 View on Map
Sustained Winds: 80.55mph
Moving:W at 3.02mph
Pressure: 968mb - Falling
156 mphCategory 5
131 - 155 mphCategory 4
111 - 131 mphCategory 3
94 - 110 mphCategory 2
74 - 95 mphCategory 1
39 - 73 mphTropical Storm
< 39 mphTropical Depression
Powered by PCWeather Products.View Full Storm Information
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Quoting TreasureCoastFl:
I dunno. Would work better for me if it were Brad Pitt maybe.
I did not know that was an option. If so, I vote yes and have some other suggestions. :)
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Quoting weatherh98:
every time theres a jog west the texans pull out those fancy maps

isaac pulls out his muddle finger and goes north


LOL
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angela said three to six hours and i think we are at 2 1/2 hours so should return northerly notion again, patience is key with these tempermental cat 1s and shortwaves
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Quoting hurricanejunky:
FYI, for those interested, DirecTV channel 349 is Hurricane Isaac Info channel...now showing Fox 8 News Feed...WVUE


That's not Hi-Def!!!! Can't watch my Hurricane coverage in Low-Def
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walking out to Bayou St. John to get a picture.... will report back.

in NOLA, 70119 zip.

walking out at 22:32 local.
Orleans and Bayou St. John area.
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Quoting HurricaneHunterJoe:


It's cheaper and shareholders dividends would be lower if they buried them. Can't have that.
it amazases me. i lived on marco when wilma came, they had the strictest building codes from the beginning. wilma direct hit lotta pool cages gone but that was the bulk of the damage. but we still had power lines not buried.
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New steering.




Sloooow mover.
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Quoting Patrap:
Nola Roux with first two..


Awesome!

I want one!

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Quoting txag91met:
Uh, this is going to farther west than what NHC thinks, that ridge is too strong over the Midwest. Why is NHC ignoring the NAM, and the GFS (18z)?


Careful, you will get accused of wishcasting.
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Quoting weatherh98:


i heard him say it on the news....


Well, somebody is wrong here. Curious to see happens as we continue. Wonder if this will be Isaac's last time? Could it pull an Allison?
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Quoting Patrap:


Definitely west motion there, eye wall looking a little ragged.
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Quoting avthunder:
It totally works!
I dunno. Would work better for me if it were Brad Pitt maybe.
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Pat:

You are a genius at adopting pups to new home.
Member Since: July 10, 2005 Posts: 3 Comments: 1281
Quoting Patrap:


Moving West, huh? How are you holding up? Did you evacuate to somewhere else?
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The Weatherbell predictors hit this just right.
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Quoting tennisgirl08:


Local mets in Gulf Shores are really getting pounded right now. Surprised at the strong conditions there. Not real bad in Mobile, right now.

Getting noisy again here on the Westside of P-cola, too. Figure it'll be like that all night long.
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Diabellico, I live off of the SE Gen Degaulle area
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Quoting skycycle:
Does anyone have an idea of the lowest pressure of any landfalling Category 1 in the Atlantic basin? I'm guessing Isaac should be up there within the top 10?



Link
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Quoting HurricaneHunterJoe:
Parish prez saying the mayor of Grand Isle reports wind gusts to 120mph


I don't doubt it based on the pressure and the newly formed eye wall...

Earlier, this cell was moving 86kts or about 99mph. Right now it has slowed to "only" 72knots, which is still 83mph.


G7 43 dBZ 7,000 ft. 2 kg/m² 0% chance 0% chance 0.00 in. 72 knots ESE (108)
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Quoting Patrap:


Yeah..she iz a good Dog and a Good Mamma fo sho'

Thanks for sharing this bright spot in a dark night :)
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Waveland, MS from Reed Timmer.
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FYI, for those interested, DirecTV channel 349 is Hurricane Isaac Info channel...now showing Fox 8 News Feed...WVUE
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Quoting Patrap:
Nola Roux with first two..


awwww, love puppies!
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Quoting weatherh98:
every time theres a jog west the texans pull out those fancy maps

isaac pulls out his muddle finger and goes north
LOL! Ya gotta let the mudlandfall mudslinging go..
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Uh, this is going to farther west than what NHC thinks, that ridge is too strong over the Midwest. Why is NHC ignoring the NAM, and the GFS (18z)?
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Quoting weatherh98:
every time theres a jog west the texans pull out those fancy maps

isaac pulls out his muddle finger and goes north


I have no desire for it to come my way. been through many of them and have no desire whatsoever to do it again. BUT... I am prepared at all times should one come my way.
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MSY reporting 50 mph. Last gust here in Gentilly sounded significantly higher.

Eye does look funky on radar. Is a new, smaller eye trying to form?

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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.