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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The wind is roaring again.... Thanks Levi and TomTaylor for the quick update.... Need to save laptop battery power... Check back in several hours.... TA
Member Since: July 4, 2005 Posts: 204 Comments: 8898
He is seriously stuck. There's not much except a slow drift sorta westish that he can do until something changes with steering. I don't see any clear draw right now that isn't countered.

This whole thing, from frustrating maybe-I'll-intensify-oh-nevermind for days to now intensifying and being flat out stuck -- truly bizarre.
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Quoting Stormchaser121:

Storm moving due west. Motion is to continue. Might hit TX now...



I look for your posts because I know they will contain info I can use. What kind of timeline? I know nothing is set in stone - just want to hear your thoughts.
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Quoting SETXborda:


So, if we are on the border of LA/TX and Lake Sabine...r we in warning or not?


We've been under a tropical storm watch all day still are.
Member Since: August 24, 2010 Posts: 0 Comments: 252
LOPL1 (28.885 N 90.024 W) is reporting winds W @ 6 knots and pressure of 28.59

http://www.ndbc.noaa.gov/station_page.php?station =lopl1
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Quoting sunlinepr:
Its going to intensify OVER land?
I guess it will be over the great lakes....






It's over-played.

GFDL and HWRF are terrible with high latitude storms.

Still, it maybe got fed this data.



It IS possible for a TD or TS or a sub-tropical storm to form over the great lakes under the right conditions, so maybe re-intensification isn't out of the question either.
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Rain is starting to pile up:




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Levi now that its slow, getting your meteorology degree, how many physics classes do you have in fluid dynamics?
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Quoting Stormchaser121:

Storm moving due west. Motion is to continue. Might hit TX now...


such confusion, likely won't pan out till morning.
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Euro comes out in an hour or so right? curious to see how it handles the current situation, how far west it takes it before landfall
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Quoting floridaT:
ohhh so youll be the guy mistiming all the traffic lights. lol


AKA King of the tailgate parties.
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LOPL1 is a data buoy that had 60 mph winds an hour ago and now has hardly any winds so it must be in the eye. I wish I new how to copy and paste but not sure how to do so if someone can do that it would be nice. The waves were 22 feet earlier and location of the buy is just about the site of the eye of the storm. If someone knows how to post please do because then we will know when the backside of eye kicks back in.
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...ISAAC MOVING SLOWLY ALONG THE COAST OF SOUTHEAST LOUSIANA 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 GetReal:



What is the forward speed???


NHC has it at 7mph WNW as of midnight CDT, about 20 miles offshore.
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Quoting bluebonnetgirl:
Just curious how far west do they think it will go before it starts going NW again??? What are the latest models showing? I'm in SETX and I'm just curious.


It's not moving very fast. It will take about 24 to 36 hours for the storm to make it's closest approach to Baton Rouge.
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nacondra norwood just said it looks like its doing a huge wobble and is not moving west or north. she didn't say this but her hand motions said she thinks it may be going to se making a big wobble. i guess maybe a loop. she said she thinks its doing a big loop. will the northshore get into some big winds soon? and if this is really looping could it get any stronger? tia!
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Quoting Levi32:


Hey GR hope you're doing ok.

Recon just went through and the pressure is 969mb, pretty steady since 6 hours ago. Long-term mean motion is very slow to the WNW just offshore.



What is the forward speed???
Member Since: July 4, 2005 Posts: 204 Comments: 8898
In the image below I have plotted all the vortex center fixes from the NOAA and USAF recon planes to show the cyclonic loop I mentioned. Lines are drawn to show the path the storm took. Obviously the storm didn't travel in a straight line, but it gives you a rough idea of the path. Rapid scan imagery shows that cloud tops directly over the center have gradually been warming throughout the night which is a sign of weakening. Pressures plotted in the image below show that minimum sea level pressures have risen 2mb from the last two vortex messages indicating the storm has weakened some. Still, as long as Isaac is over water there is potential for Isaac to strengthen is there as long as he remains over water, but I suspect the close proximity to land and upwelling may be limiting significant bursts of convection to fire up again, thus preventing the storm from undergoing any significant bouts of intensification.

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Its going to intensify OVER land in 108 hrs.???
I guess it will be over the great lakes.... (Looks like this has to be updated)





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NHC says WNW AT 7 now
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Quoting NeverPanic:


Not much I can see to pull him east.
Go west young man?
Surprising that few, if any, picked up on this conundrum.


rhis steering layer would suggest he cant go anywhere but northeast

Link
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Quoting TexNowNM:

Storm moving due west. Motion is to continue. Might hit TX now...
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Quoting MercForHire:


Urban Planning & Cartography

I design rush-hours. :)
ohhh so youll be the guy mistiming all the traffic lights. lol
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Quoting GetReal:
Checking in for a few moments from the Westbank (south side) metro NOLA,,,, Needless to say been without power for since around 4:00pm.... Wide spread power outages, and trees falling in the area. The usual debris blowing down the street with 55-65mph sustained winds. I have seen some gust that had to be near 90mph

just watched radar loop what is expected with this unexpected SW move back into GOM???

Please provide latest RECON info if any....


Hey GR hope you're doing ok.

Recon just went through and the pressure is 969mb, pretty steady since 6 hours ago. Long-term mean motion is very slow to the WNW just offshore.
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looks like the eye is tightening and hes squeezing that dry air out pretty good.
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Looks like HH setting up for 6th pass. What is the normal amount of passes?
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Im believing now that the TX coast will get hit. GFS...you win!
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Quoting Stormchaser121:

NOW!!!

What is happening. We are back in hospital so missed what
Quoting Stormchaser121:

NOW!!!


What is happening. We are back in hospital (NM) so missed what is going on in Orangefield and Bridge City? What about Beaumont? Kid in school there and she is from the desert, literally. I am out of the loop.
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Quoting bluebonnetgirl:
Just curious how far west do they think it will go before it starts going NW again??? What are the latest models showing? I'm in SETX and I'm just curious.

They are just as surprised as we are.
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Quoting bluebonnetgirl:
Just curious how far west do they think it will go before it starts going NW again??? What are the latest models showing? I'm in SETX and I'm just curious.

Where in SE TX are you?
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Quoting floridaT:
outstanding a degree in?


Urban Planning & Cartography

I design rush-hours. :)
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how do i post a radar loop?..and wow this is gonna be really bad. Katrina like possibly..the storms not moving at all right now just wobbling around in a cirlce right now...even if it starts going right now in a particular direction and even gains speed its gonna dump like 15+ inches of rain in all them ares down there including NO and mobile..looks like hes getting stronger possibly too? gonna be a long 18 hours or more for everyone in this storm
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If Issac heads more west and then finally goes north, I hope Kansas receives some rain from him. The drought here is insane!
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Quoting want2lrn:
So a question. If Isaac just kind of sits there and "wears" itself out and starts to break up, would the steering that is keeping him from moving North (nudging to the west)carry the remnants into Texas and help with some drought relief?


No, this steering would likely pull a weaker storm along the front much quicker. A more powerful storm has a better chance of moving further west into those areas.
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Just curious how far west do they think it will go before it starts going NW again??? What are the latest models showing? I'm in SETX and I'm just curious.
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Quoting SETXborda:
In Bridge City, when should I go stock up? Maybe if it gets as far as Morgan City?


I'd just keep an eye on what the NHC says at this point.
Member Since: August 24, 2010 Posts: 0 Comments: 252
Quoting TexNowNM:


Are you in BC too. We are from Orangefield. At home in Tx is also from our neck of the woods.

How is the weather? Cousin said some gusts.


I am from O-field but living in Port Neches now. wind has been blowing and high clouds working in.
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Quoting tennisgirl08:


Huh?

He's a famous hurricane chaser. I don't agree what he said imo.
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Quoting HurricaneHunterJoe:


How can these wind speeds be like this? hearing 100-120 is that possible in a 80mph hurricane?? Why is the nhc not reporting that?


So people don't panic?

Talking about people taking these storms seriously, and not doing that themselves, at least if people were confronted with a stronger system, they'd be taking better precaution. I recall the "even if the storm may be stronger" bit in an advisory on Chris when he was clearly a hurricane. It's not quite the same detail, because he did not make landfall anywhere, but this year it seems attention spans are off. I've always kind of considered Isaac a Category 2 since the afternoon, and his pressure is that of a major. It's not very far above the surface that winds above cat 1 are being experienced.

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Checking in for a few moments from the Westbank (south side) metro NOLA,,,, Needless to say been without power for since around 4:00pm.... Wide spread power outages, and trees falling in the area. The usual debris blowing down the street with 55-65mph sustained winds. I have seen some gust that had to be near 90mph

just watched radar loop what is expected with this unexpected SW move back into GOM???

Please provide latest RECON info if any....
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Quoting sunlinepr:


Geez, not Shepard Smith again. No levees were overtopped. Bourbon Street is empty because there are 4,000 National Guard troops on the ground, armed and ready. Itchy trigger fingers lead to empty streets. :)
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Storm surge from Waveland mississippi, getting worse then this apparently.

Link
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Quoting want2lrn:


Know that area well, i was the Asst Golf Pro (when it was still Skyline Country Club) for about 3 years. Keep your head down and stay safe!


cool...if you ever came into the bank out by the campus then probably saw you..
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So a question. If Isaac just kind of sits there and "wears" itself out and starts to break up, would the steering that is keeping him from moving North (nudging to the west)carry the remnants into Texas and help with some drought relief?
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Quoting sar2401:


Is he a storm chaser or what? Doesn't seem to know a lot about weather. :) I do notice all the lights are still on. It's apparently not hitting the French Quarter too hard. Looking at the Entergy outage map for Louisiana, there are surprisingly few outages outside the immediate New Orleans area.


For me he's someone vac. or staying in Bourbon and made that YT video...
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Quoting SomeRandomTexan:


I know your sis... she told me you were on here.


Are you in BC too. We are from Orangefield. At home in Tx is also from our neck of the woods.

How is the weather? Cousin said some gusts.
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Quoting KEEPEROFTHEGATE:

Wow, what does this mean. That's so crazy,
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New advisory "WNW" now instead of "NW"


Hurricane ISAAC Public Advisory

Home Public Adv Fcst Adv Discussion Wind Probs Graphics Archive

US Watch/Warning

000
WTNT34 KNHC 290453
TCPAT4

BULLETIN
HURRICANE ISAAC INTERMEDIATE ADVISORY NUMBER 32A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
1200 AM CDT WED AUG 29 2012

...ISAAC MOVING SLOWLY ALONG THE COAST OF SOUTHEAST LOUSIANA AND
PRODUCING A DANGEROUS STORM SURGE...FLOODING FROM RAINFALL ALSO
EXPECTED...


SUMMARY OF 1200 AM CDT...0500 UTC...INFORMATION
-----------------------------------------------
LOCATION...29.0N 90.0W
ABOUT 60 MI...95 KM SE OF HOUMA LOUISIANA
ABOUT 70 MI...110 KM S OF NEW ORLEANS LOUISIANA
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...969 MB...28.61 INCHES
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Quoting TampaFLUSA:
Lol
RT @reedtimmerTVN: Hurricane #Isaac may have stalled over open water, and possibly started a wobble back northeast! Could be strengtheni ...


Huh?
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.