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 allancalderini:
Have you receive rain athome?


Nope not a drop. Beautiful day today. :)
Member Since: August 24, 2010 Posts: 0 Comments: 253
Quoting MercForHire:


Urban Planning & Cartography

I design rush-hours. :)


Is that related to designing traffic jams? Lol -
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Quoting wxchaser97:

That would be interesting as I'm in Michigan.



Me too. In Grand Rapids
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Quoting AtHomeInTX:


I agree with your Isaac track. My brain can't get started on the other one yet. :) Anyway, I've been calling for a Gustav track for days. Lol. If I'm wrong I'll eat my first crow.


hang in there girl
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Quoting Levi32:


More likely starting to collapse a bit given warming cloud tops in the eyewall and likely cooler SSTs beneath it now due to evaporation.


Hey Levi what are your thoughts on the latest westward wobbles or trend...do you think the latest model guidance is valid in bringing Isaac wnw into parts of Tx?
Member Since: May 31, 2011 Posts: 57 Comments: 572
Quoting sarahjola:
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!
can someone give me some understanding as to what i am hearing from nacondra norwood on channel 8 news? thanks!
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Quoting wxchaser97:


I agree with your Isaac track. My brain can't get started on the other one yet. :) Anyway, I've been calling for a Gustav track for days. Lol. If I'm wrong I'll eat my first crow.
Member Since: August 24, 2010 Posts: 0 Comments: 253
i agree kirk looks like it means business maybe it will go against all odds and not recurve. looks to be moving fast. won't suprise me one bit
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Quoting wxchaser97:
Kirk wants attention:
May be up to 50 or 60 at the next advisory imagine if he strength into a hurricane so much for rip.LOL XD.
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Quoting thesweetlycool:


Lake Michigan is especially warm this year!

That would be interesting as I'm in Michigan.
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Quoting hericane96:
i think the worst case would be for Isaac to drift of the coast of la for a while strength then move back over the same area heading n then ne catching the next trough.which would create higher storm surge and massive flooding. But thats highly-highly unlikley.


Or if the wind picked up sharks and alligators and dropped them in New Orleans along with just enough water for the sharks to be submerged. Did I mention that the alligators were terrorist suicide bombers each carrying a thermo-nuclear device and a burlap sack of unpopped popcorn? Work that out GFS.
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Quoting AtHomeInTX:


We've been under a tropical storm watch all day still are.
Have you receive rain athome?
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Quoting WetBankGuy:
Eye is getting goofy again on radar. Two bands curving in. Is it trying to form a new eyewall (or two?)


Station SPLL1
LSU CSI
Location: 28.867N 90.483W
Date: Wed, 29 Aug 2012 02:00:00 UTC
Winds: NNW (330°) at 63.9 kt gusting to 76.9 kt
Significant Wave Height: 8.5 ft
Dominant Wave Period: 7 sec
Water Temperature: 82.6 F
Visibility: 1.9 nmi


More likely starting to collapse a bit given warming cloud tops in the eyewall and likely cooler SSTs beneath it now due to evaporation.
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I wrote a new blog on Isaac, Kirk, and 98L
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Quoting all4hurricanes:
Does Kirk have an eye?


Yep.

KIRK
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NATIONAL WEATHER SERVICE LAKE CHARLES LA
1209 AM CDT WED AUG 29 2012

.AVIATION...HURRICANE ISAAC WILL SPREAD LOW CLOUDS, RAIN, AND VERY
GUSTY WINDS INTO THE AREA THROUGH TONIGHT AND WEDNESDAY. WINDS AT
ALL TERMINALS WILL INCREASE AROUND SUNRISE AND THROUGH THE DAY
WITH WIND GUSTS INCREASING TO AROUND OR OVER 40 KNOTS AT MOST
TERMINALS WHILE THE SYSTEM MOVES BY. WIDESPREAD RAIN WILL CREATE
LOWER VIS WITH MVFR OR IFR CONDITIONS POSSIBLE.

Member Since: May 31, 2011 Posts: 57 Comments: 572
Eye is getting goofy again on radar. Two bands curving in. Is it trying to form a new eyewall (or two?)


Station SPLL1
LSU CSI
Location: 28.867N 90.483W
Date: Wed, 29 Aug 2012 02:00:00 UTC
Winds: NNW (330°) at 63.9 kt gusting to 76.9 kt
Significant Wave Height: 8.5 ft
Dominant Wave Period: 7 sec
Water Temperature: 82.6 F
Visibility: 1.9 nmi
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Kirk wants attention:
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nacondra norwood said eye reforming. what can this mean for new orleans and st. tammany parish? tia!
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Quoting sunlinepr:
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)







Lake Michigan is especially warm this year!
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Quoting TomTaylor:
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.


do you think it will go back to tracking northwest?
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Quoting SomeRandomTexan:
Energy had stated a day or 2 ago that with the drought from last year a lot of trees are weak now and any wind could topple trees or break limbs.



Yes, they said during the winter, too. Houston chronicle had an article that said that area could lose 10 percent of its trees from last years drought. Scary thought when you factor in wind.
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02Z HRRR shows hardly any movement for 15 hours.

Composite Reflectivity
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I'm going to sleep for a while. Tomorrow is a long day.
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Here in Pensacola we had almost 24 inches of rain in 48 hours already this year. 12 inches of rain along the gulf coast isn't unusual. There will be localized flooding but nothing out of the ordinary. Inland perhaps.. But not here...
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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?


Because the NHC were perhaps a little off on their "extrapolations"? Someone on the blog this afternoon (sorry cannot find it now) said that perhaps the Saffir-Simpson Scale is due for a bit of a tweak with regards to storm size and the correllation of barometric pressure to a higher category storm.

It was mentioned that last year Irene was "down-catted" as well, so perhaps this could be a new trend?

"Irene recorded a low pressure of 942 millibars as a Category 3 storm. In smaller systems, a pressure reading this low would likely produce a Category 4 storm with winds over 130 mph." (from an article in Huffington Post)

No expert at all, just seconding an observation I read earlier and some evidence that Isaac has Cat 2 winds being reported.


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Does Kirk have an eye?
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Quoting TexNowNM:



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.

Its moving very slow, W/WNW. I see this following the GFS model...and i think that this may actually hit the TX/LA border as a cat 1. You need to be prepared, and listen to local media outlets for further information. Soon, i believe we will be in a Tropical storm warning. If it continues west, then we will be under a hurricane watch. Thats my thoughts.
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It's pretty much stalled now.
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Quoting SETXborda:


I know, but looking at offshore, it is a warning...did not notice it earlier tonight!


I noticed that too. weird...
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Checking in from new Iberia . Just north of vermillion bay.. If Isaac keeps coming west it will be under me before too long.. Winds here out of the north east at 30 with gusts to 40 .
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Quoting RTSplayer:


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.


This is an amazing statement, please provide history of such. These are cold waters and I have never heard of such in my experience except in movies.
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Quoting tennisgirl08:


Please see my earlier post. He is not expected to hit TX.


Wrong...most models including the 00Z GFS, NAM, 12Z Nogaps...even the 12Z Euro bring Isaac through at least east Texas!
Member Since: May 31, 2011 Posts: 57 Comments: 572
Quoting KEEPEROFTHEGATE:


He's basically stalled just south of Grand Isle. Not good for them.
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Quoting NJcat3cane:
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


No, he's not going to dump 15+ inches all over the area. He's not getting stronger. Pressures have been steady the last 6 hours and cloud tops are warming. It's certainly not Katrina-like. Don't you have school or something in the morning?
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Quoting AtHomeInTX:


We've been under a tropical storm watch all day still are.


I know, but looking at offshore, it is a warning...did not notice it earlier tonight!
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Entergy had stated a day or 2 ago that with the drought from last year a lot of trees are weak now and any wind could topple trees or break limbs.
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Quoting tennisgirl08:


Please see my earlier post. He is not expected to hit TX.
whats expected and what happens this year are atypical
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A 10 inch 24 hour rainfall total!?

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i think the worst case would be for Isaac to drift of the coast of la for a while strength then move back over the same area heading n then ne catching the next trough.which would create higher storm surge and massive flooding. But thats highly-highly unlikley.
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There is another short wave on its way.
Water Vapor Loop

Goodnight Isaac. Behave yourself.
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http://classic.wunderground.com/radar/radblast.asp? zoommode=pan&prevzoom=zoom&num=40&frame=0&delay=15 &scale=1.000&noclutter=0&ID=LIX&type=N0R&showstorm s=99&lat=0&lon=0&label=you&map.x=400&map.y=240&sca le=1.000¢erx=400¢ery=240&showlabels=1&rain snow=1&lightning=1&lerror=20&num_stns_min=2&num_st ns_max=9999&avg_off=9999&smooth=1
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Pressure has bottomed out at Grand Isle, Louisiana. Minimum pressure reached was around 975mb as the storm passed to the south of the station.

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Quoting RTSplayer:


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.


Hazel! People in southern Ontario (who are old enough) remember her, she's still Canada's worst natural disaster in history, I think. She practically dismantled Toronto with her tropical rains.
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Cantore reported Katrina was the "worst nightmare" to ever happen to New Orleans. I'd beg to differ... http://www.nola.com/175years/index.ssf/2011/08/185 3_terrifying_yellow_fever_e.html
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Eye trying to broaden further? FCOL! Bubba!


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NO local updates on our tv stations, I wonder if they are waiting too, when would it be too late to advise SETX of Tropical Storm Warning, it doesn't take much for the power to go out, much less, limbs to fall on lines...some people are really not even worried...it amazes me!
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Quoting TexNowNM:



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.


Please see my earlier post. He is not expected to hit TX.
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Quoting Stormchaser121:

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


Its just wobbling south.. its not going anywhere right now
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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

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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.