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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Looks like more WNW motion now, could be radar loop
illusion...
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Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting CybrTeddy:
Via Grand Isle Mayor: Island has significant damage and water on the island is waist deep


Last Air Force run showed the strongest winds in the NW quadrant. Radar velocities were showing this as well. However, they are down from earlier this evening.

Definitely heading westward at a faster pace now.

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Quoting mcluvincane:
Isaac worse than Gustav ever thought of being
Really? What's happening? It does look like he got strong just as he reached the coast. Still a little offshore so not weakening. Not a good scenario! Hope he weakens soon.
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Quoting HopquickSteve:


If the inner eye had completed, then "landfall" err "swampfall"...since it hadn't, I'd say no landfall, but the NHC has used it's empirical (imperical) fiat to declare it so. :p
Yeah, I have no problem with the NHC calling it. Was more disappointed in the local met running with it like it was the end of the storm. Pitiful for a guy that's been doing the weather in NOLA since I was in HS. I'm 43.
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Now I see why I had a bad feeling over the past few days, cause there is something bad happening still.
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Quoting Hurricane12:
Thanks, Dr. Masters.

This is a very serious storm. I hope the levees hold.


I second all of that.

Isaac's strange eyewall design makes one wonder what we'll see next. History in the making!
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Quoting mcluvincane:
Isaac worse than Gustav ever thought of being


Gustav weakened as he came in, right? Isaac's def. not doing that. Crazy storm.
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Quoting kidd5433:


Carry the one...oh hell Im not doing math tonight
nearly 500000 gals a minute if my math is right lol
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NAM at 45 hours..

Member Since: August 18, 2011 Posts: 0 Comments: 635
Quoting DavidHOUTX:


LOL This is completely slacking. NOLA current conditions... SNOW???



Now, that's hilarious!
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Quoting jake436:


Those maps under the radar are VERY deceiving. That's not 'land'. That finger of 'land' that it crossed when they called 'landfall' is Southwest Pass. SW Pass is literally rip rap and water hyacinths. That's it. There's no 'land' there.
Amazingly, even the met in NOLA on WWL reported it as landfall, of course parroting the NHC. But he took it a step further that he should know better than to do. He said it would start weakening now that it's made 'landfall'. And he's been a met there for 20+ years. Poor reporting. At landfall, I usually try to watch local news, because you SHOULD be able to get info from someone that SHOULD know the local terrain/area. Apparently Mr. Arredondo does not. Of course it's back over water now. It never WAS over land.


If the inner eye had completed, then "landfall" err "swampfall"...since it hadn't, I'd say no landfall, but the NHC has used it's empirical (imperical) fiat to declare it so. :p
Member Since: May 17, 2006 Posts: 0 Comments: 635
Quoting weatherh98:
remember when we thought isaac would go for the fishies?

i must be a fish now

The same could happen with 98L going into the Caribbean instead of out to sea, hopefully not though.
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Quoting weatherh98:


i can hear trees falling
ut oh. hope ya have a safe room..
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Quoting aislinnpaps:
Just talked to my son in Navarre. He's at home and all is well. His cell phone signal hasn't worked well today but never lost electric.


aislin...is he on the island itself? I'm curious about the beach erosion. It was bad when I was there in July. I'm glad he is safe :)
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Isaac worse than Gustav ever thought of being
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size matters...
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Quoting TreasureCoastFl:
I dont expect any of ya out there to have power after about midnight.. would be surprised


i can hear trees falling
Member Since: June 17, 2011 Posts: 11 Comments: 6539
Just talked to my son in Navarre. He's at home and all is well. His cell phone signal hasn't worked well today but never lost electric.
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Quoting shfr173:
NOLA new pumping system capable of pumping 8000 gal a sec x 8 pumps!!! do the math


Carry the one...oh hell Im not doing math tonight
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Quoting Category5HitsFl:




This is only the Western part of the storm as well, although I bet it does not help to be on a barrier island and to have the water also moving in from the North with the bands wrapping around from that direction.
The island runs from NE to SW directionally.
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Quoting Nerull:


You know what the 'A' in AWOS stands for, right?


automated?
Member Since: August 18, 2011 Posts: 0 Comments: 635
The area between where Isaac made landfall and Grand Isle is open water, and is about 30nm . No wonder water is waist deep on the island..
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Quoting LillyMyrrh:

Yeah, it's a tropical storm watch over Orange and Jefferson Counties.


Oh, I totally missed that that had been issued.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting TreasureCoastFl:
They actually just talked about Kirk on TWC...


Lol, he said it was of no importance its going out to sea
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remember when we thought isaac would go for the fishies?

i must be a fish now
Member Since: June 17, 2011 Posts: 11 Comments: 6539
Quoting AllyBama:
Rain and wind has picked up again and from the looks on radar will be here for awhile. Guess it was about time - lol


Agreed! Lots of rain which is here to stay.
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Lots of rain, wind, and surge for extended periods of time is not good.
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Quoting angiest:


They show a small patch of either ts watch or ts winds in Texas there.

Yeah, it's a tropical storm watch over Orange and Jefferson Counties.
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Quoting weatherh98:
I dont expect to continue ton have power in the next few hours.
I dont expect any of ya out there to have power after about midnight.. would be surprised
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Quoting TropicalAnalystwx13:

Thank god it didn't have that attitude when it moved off the coast of Cuba.


The low pressure area & surface trough in the Caribbean was a game changer in the life of Isaac. Thank God for that.
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if the guy in the weather channel says Propagating one more time I'm thinking he took bets with his buddies to how many times he could say that word on air...
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Quoting CybrTeddy:
Via Grand Isle Mayor: Island has significant damage and water on the island is waist deep
There's VERY few structures on the island that aren't raised 10'+ off the ground. Grand Isle always gets the worst of the storms, though.
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Quoting DavidHOUTX:


Was it accuweather reporting it? That is just ridiculous.


LOL, no. Obviously a glitch somewhere.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting wxchaser97:

Maybe more as Isaac just sits there with continued bands coming band. Stay safe Harrison.


the more it sits the more moisture the looser the soil the heavier the winds.... its inevitable
Member Since: June 17, 2011 Posts: 11 Comments: 6539
Quoting cajunkid:
Link

not good


Hmmm - I looked at some of the other charts... There's a lot of water that needs to go somewhere.
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Quoting DavidHOUTX:


LOL This is completely slacking. NOLA current conditions... SNOW???


You know what the 'A' in AWOS stands for, right?
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Quoting weatherh98:
I dont expect power in the next few hours.

Maybe more as Isaac just sits there with continued bands coming band. Stay safe Harrison.
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Quoting Stormchaser121:

now where is THAT one going??


GFS in fantasyland says fish storm.
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Quoting CybrTeddy:
Via Grand Isle Mayor: Island has significant damage and water on the island is waist deep




This is only the Western part of the storm as well, although I bet it does not help to be on a barrier island and to have the water also moving in from the North with the bands wrapping around from that direction.
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*
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NOLA new pumping system capable of pumping 8000 gal a sec x 8 pumps!!! do the math
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Quoting angiest:


They show a small patch of either ts watch or ts winds in Texas there.


NWS out of Lake Charles says we could get 30 MPH winds with gusts up to 45 in Southeast Texas. Up to 6" rain.
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Quoting mcluvincane:
Please refrain from talking about kirk fplease
They actually just talked about Kirk on TWC...
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Quoting angiest:


I remember seeing some weather station in NE Texas report something like 105 degrees with blowing snow during the summer.


Was it accuweather reporting it? That is just ridiculous.
Member Since: August 18, 2011 Posts: 0 Comments: 635
Quoting mcluvincane:
Please refrain from talking about kirk fplease

What r u talking about Kirk is Awesome!!!!! :p
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Quoting Felix2007:
So neither Isaac nor Kirk will be the big bad wolf of the hurricane season, but Leslie will??? Doesn't sound like a very threatening name.

now where is THAT one going??
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I dont expect to continue ton have power in the next few hours.
Member Since: June 17, 2011 Posts: 11 Comments: 6539
Interesting.

TROPICAL STORM KIRK DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
1100 PM AST TUE AUG 28 2012

A LARGE CONVECTIVE BURST...WITH A LARGE AREA OF CLOUD TOP
TEMPERATURES COLDER THAN -70C...HAS PERSISTED NEAR AND TO THE NORTH
OF THE CENTER OF THE TROPICAL CYCLONE FOR THE LAST SEVERAL HOURS.
AN ASCAT PASS FROM 2338 UTC SHOWED RELIABLE WIND VECTORS NEAR 40 KT
OR PERHAPS A LITTLE HIGHER. THEREFORE...THE INITIAL INTENSITY IS
CONSERVATIVELY SET AT 40 KT...AND THE SYSTEM IS UPGRADED TO
TROPICAL STORM KIRK. THE INTENSITY FORECAST IS TRICKY. THE SHIPS
MODEL SHOWS SOUTHWESTERLY SHEAR REMAINING GENERALLY BETWEEN 15 AND
20 KT FOR THE NEXT SEVERAL DAYS. IN ADDITION...GOES-R IMAGERY SHOWS
A SIGNIFICANT AMOUNT OF DRY AIR WEST OF THE CYCLONE. WHILE THESE
CONDITIONS SEEM UNFAVORABLE FOR SIGNIFICANT INTENSIFICATION...THE
SHIPS AND LGEM MODELS SUGGEST THAT KIRK COULD BECOME A HURRICANE IN
A FEW DAYS. THE OFFICIAL FORECAST HAS BEEN ADJUSTED SIGNIFICANTLY
UPWARD BUT IS STILL BELOW THE STATISTICAL-DYNAMICAL GUIDANCE.

RECENT MICROWAVE DATA HAS HELPED LOCATE THE CENTER OF KIRK...AND THE
INITIAL MOTION ESTIMATE IS A MORE CONFIDENT 280/10. A CONTINUED
WESTWARD TO WEST-NORTHWESTWARD MOTION AT ABOUT THE SAME SPEED IS
EXPECTED DURING THE NEXT DAY OR TWO. AFTER THAT TIME...A GRADUAL
TURN TO TOWARD THE NORTH AND THEN NORTHEAST WITH A FASTER FORWARD
SPEED IS FORECAST AS THE SYSTEM REACHES THE WESTERN EDGE OF THE
SUBTROPICAL RIDGE AND BECOMES INFLUENCED BY AN APPROACHING LARGE-
SCALE TROUGH. THE LATEST GFS RUN HAS A MUCH DEEPER SYSTEM AND...AS
A RESULT...HAS SHIFTED WELL TO THE EAST WITH RECURVATURE OCCURRING
AROUND 50W. THE NEW OFFICIAL NHC FORECAST CONSIDERS THE GFS AN
OUTLIER AT THIS TIME AND REMAINS ON THE WEST SIDE OF THE MODEL
GUIDANCE ENVELOPE...CLOSEST TO THE ECMWF SOLUTION.


FORECAST POSITIONS AND MAX WINDS

INIT 29/0300Z 23.9N 45.0W 40 KT 45 MPH
12H 29/1200Z 24.2N 46.6W 45 KT 50 MPH
24H 30/0000Z 24.5N 48.6W 50 KT 60 MPH
36H 30/1200Z 25.0N 50.9W 55 KT 65 MPH
48H 31/0000Z 26.0N 52.9W 55 KT 65 MPH
72H 01/0000Z 29.0N 55.3W 55 KT 65 MPH
96H 02/0000Z 34.8N 52.9W 55 KT 65 MPH
120H 03/0000Z 42.3N 44.9W 55 KT 65 MPH

$$
FORECASTER KIMBERLAIN/CANGIALOSI
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Quoting Felix2007:
So neither Isaac nor Kirk will be the big bad wolf of the hurricane season, but Leslie will??? Doesn't sound like a very threatening name.
Well Katrina didnt sound so formidable as a name either did it?
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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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