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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Using the WC map, if the current position is center of whats left of the eye, then Isaac has travelled 28 miles in 2 hours.

Nice to see the pick up in forward speed.
Member Since: Posts: Comments:
Quoting jpsb:
That is what the TWC said, we shall see if that holds true.
Land in a metaphorical sense, or if you believe old maps. It won't hit something most readers here would recognize as land until it gets well up into Terrebonne Parish near Houma. And I'm talking about the precip circulation, not the satellite presentation.
Member Since: September 19, 2007 Posts: 0 Comments: 287
BULLETIN
HURRICANE ISAAC ADVISORY NUMBER 33
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
400 AM CDT WED AUG 29 2012

...ISAAC BEGINNING TO MOVE INLAND IN SOUTHEAST LOUISIANA...DANGEROUS
STORM SURGE AND FLOOD THREAT FROM HEAVY RAINS LIKELY TO CONTINUE
THROUGH TODAY AND TONIGHT...


SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...29.2N 90.5W
ABOUT 30 MI...50 KM SSE OF HOUMA LOUISIANA
ABOUT 60 MI...95 KM SSW OF NEW ORLEANS LOUISIANA
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...969 MB...28.61 INCHES
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70119 here. Just lost power for good it looks like.. It was a good run...
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Eyewall is indeed tightening up, but in the last hour you can see Isaac make a decent jog to the WNW, which has put a little more of his eye on the coast. Frictional effects are most likely in play here.

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Quoting jpsb:
That is what the TWC said, we shall see if that holds true.


Was just wondering about that myself. The 2 am CDT position is still over water and jibes with the IR satellite presentation. Someone at TWC must also be looking at the radar, as the center of the precip circulating in the storm looks to me just about overland and traveling past the ironically named Golden Meadow on Highway 1 headed for Houma.

Member Since: September 19, 2007 Posts: 0 Comments: 287
Quoting CoopsWife:
Morning all - just a quick glance at the discussion makes me not so happy this morning - going to be a long day.

I will read back through the night's posts while fixing breakfast. In the meantime, help yourselves to coffee the virtual breakfast bar. Watch out for the biscuits in the red basket - peppers in them for the ones who like it spicy.



Oh man, you should not talk about breakfast, I am working night shift and I ate all my food hours ago!
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The ASOS at Lakefront is reporting snow again....guh!

KNEW 290832Z 09043G56KT 1/2SM SN FEW007 BKN012 OVC023 A2920 RMK AO2 PK WND 08061/0755 RAE25SNB25 P0060 FZRANO $
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Morning all - just a quick glance at the discussion makes me not so happy this morning - going to be a long day.

I will read back through the night's posts while fixing breakfast. In the meantime, help yourselves to coffee the virtual breakfast bar. Watch out for the biscuits in the red basket - peppers in them for the ones who like it spicy.

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Holy, sheesh... is the "eye" totally tightening, or what?

Link

Jo
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NWSNewOrleans ‏@NWSNewOrleans

A back levee in Plaquemines is being overtopped from the St. Bernard line all the way to White Ditch, some 18 miles. Evacuations underway.
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1158. zillaTX
blog < sleep looks like landfall 2 is perm. good luck to those impacted!!
Member Since: July 28, 2011 Posts: 0 Comments: 50
good luck bro!!
Member Since: September 18, 2010 Posts: 0 Comments: 4576
1156. GetReal
Quoting HurricaneHunterJoe:


glad ya still got power,i heard on ur local news that 342,000 have lost power



One last response... Out of power for nearly 12 hours!

Currently posting from battery powered laptop with Verizon card... Bye again
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1155. vince1
Quoting HurricaneHunterJoe:


thats what i was gonna say.....oil and correxit......or that sinkhole.

aye, one big toxic mess.
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1154. jpsb
Quoting zillaTX:


looks like it has landed for good no?
That is what the TWC said, we shall see if that holds true.
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Quoting atmosweather:


981.4 mb...same pressure reported at Houma-Terrebonne. Lotsa stuff yet to come unfortunately.


yea....hh found 964xxmb strengthening over the swampland
Member Since: September 18, 2010 Posts: 0 Comments: 4576
1152. GetReal
Quoting atmosweather:


Hang in there! Getting hit pretty hard with that eyewall convection, rainfall totals starting to go up everywhere and plenty of high winds reported.


Thanx Atmos.... I am sure some of these gust, as large trees are bending at 90 degrees have to be, or above 90 mph... I can hear stuff breaking and ripping apart in other neighbors homes. In of coarse the loud MOAN of the wind through the power lines.

Signing off again... At least it looks like Isaac is finally on the move again.... Bye for now.
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1151. zillaTX
Quoting leftlink:
IR view suggests moisture cutoff starting around 2am CDT! System start to raining itself out now that center has gone over land.



LINK


it is not "done" but looks "done"
Member Since: July 28, 2011 Posts: 0 Comments: 50
Quoting GetReal:
My current barometer reading is 28.98 inches, with winds out of the ENE at a sustained 60+ with much higher gust. I am located in Westwego, La south side of Metro NOLA.


glad ya still got power,i heard on ur local news that 342,000 have lost power
Member Since: September 18, 2010 Posts: 0 Comments: 4576
IR view suggests moisture cutoff starting around 2am CDT! System start to raining itself out now that center has gone over land.



LINK
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1148. zillaTX
Quoting jpsb:
Judging by the wind on Galveston Bay Issac is either strengthening or moving west. Breezes is getting brisk here, 15-20.


looks like it has landed for good no?
Member Since: July 28, 2011 Posts: 0 Comments: 50
Quoting GetReal:
My current barometer reading is 28.98 inches, with winds out of the ENE at a sustained 60+ with much higher gust. I am located in Westwego, La south side of Metro NOLA.


981.4 mb...same pressure reported at Houma-Terrebonne. Lotsa stuff yet to come unfortunately.
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1146. jpsb
Quoting odinslightning:


:) agreed upon :) i can agree with that
Judging by the wind on Galveston Bay Issac is either strengthening or moving west. Breezes is getting brisk here, 15-20.
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Quoting TexNowNM:
Atmos- you have been giving good info on this blog for years!


I appreciate that thank you :) We've come a pretty long way since the blog began 8 seasons ago. There will always be trolls and unnecessary drama but the quality of information and the number of great bloggers is awesome now.
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1144. GetReal
My current barometer reading is 28.98 inches, with winds out of the ENE at a sustained 60+ with much higher gust. I am located in Westwego, La south side of Metro NOLA.
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Quoting FunhouseFX:


If I understand it was NOT a Mississippi levee and it is not protected by the federal levee system. They apparently have their own levees which were not good enough.

According to him, this flooding at his home is worse than Katrina. He reported that the water was in the process of ruining everything on his second story.


ok, the only water i saw near braithwaite was the river. I see some water called big mar....i wonder if thats it?
Member Since: September 18, 2010 Posts: 0 Comments: 4576
Atmos- you have been giving good info on this blog for years!
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Quoting SELAliveforthetropic:


Thanks.... It is rough when they come through at night. You don't know what's going on.


I know, its a strange and terrible feeling. Charley and Andrew were night storms for me.
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Quoting GetReal:
Just checking in after being awakened to my 6ft wood fence and former top of the line Rubber Maid storage shed being ripped apart!!!

I invite any of those nay sayers about whimpy Isaac to change places with me right now.... No power going on 12 hours.... Probable minor roof damage at this point....

This currently is the worst of the WX we have experienced with Isaac so far, and is steadily getting worse....


Hang in there! Getting hit pretty hard with that eyewall convection, rainfall totals starting to go up everywhere and plenty of high winds reported.
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I tried to look it up and saw what appeared to be what we call a village here in NM. Also, it appeared they are still working on the levies there. I wish a poster with knowledge of that area would post.
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Quoting atmosweather:


N-erly winds, and latest reports showing sustained winds of 49 mph with gusts up to 61 mph at Houma-Terrabonne, and a pressure now down to 981.4 mb! You are still in the NW eyewall, hold on tight my friend.


Thanks.... It is rough when they come through at night. You don't know what's going on.
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1137. GetReal
Just checking in after being awakened to my 6ft wood fence and former top of the line Rubber Maid storage shed being ripped apart!!!

I invite any of those nay sayers about whimpy Isaac to change places with me right now.... No power going on 12 hours.... Probable minor roof damage at this point....

This currently is the worst of the WX we have experienced with Isaac so far, and is steadily getting worse....
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it's sad about the flooding in south la right now. all of those places used to be protected from this kind of wave action when the bayou used to spread way to the south.
Member Since: September 3, 2009 Posts: 0 Comments: 475
Quoting HurricaneHunterJoe:


mississippi river levee? wow


If I understand it was NOT a Mississippi levee and it is not protected by the federal levee system. They apparently have their own levees which were not good enough.

According to him, this flooding at his home is worse than Katrina. He reported that the water was in the process of ruining everything on his second story.
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Quoting SELAliveforthetropic:
Im in Houma can someone tell me the direction on the wind I'm getting right now . Been up too long can't think.


N-erly winds, and latest reports showing sustained winds of 49 mph with gusts up to 61 mph at Houma-Terrabonne, and a pressure now down to 981.4 mb! You are still in the NW eyewall, hold on tight my friend.
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Quoting WetBankGuy:


No. This is a known weak spot in the levee. It failed in Gustav (and of course in Katrina).

https://maps.google.com/maps?q=Braithwaite,+LA&am p;hl =en&ll=29.859553,-89.935369&spn=0.038409,0 .0739&sl l=29.5333,-89.1&sspn=0.616548,1.182404&oq= Brait&hn ear=Braithwaite,+Plaquemines,+Louisiana&t=h&am p;z=14

yea, i looked at the area,just didnt know exactly city lines saw some houses in the greater area,but wasn't sure
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Quoting SELAliveforthetropic:
Im in Houma can someone tell me the direction on the wind I'm getting right now . Been up too long can't think.


Airport's showing 50 from the north with gusts of 60
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Quoting atmosweather:


Remember they are using long-term motion, and in the last 6 hours Isaac has moved about 45 miles, which is 7.5 mph. The last 3 hours he hasn't moved much of that 45 miles though.


:) agreed upon :) i can agree with that
Member Since: September 3, 2009 Posts: 0 Comments: 475
Quoting FunhouseFX:
Don Beshel from Braithwaite is reporting that the water came over the levies and he now has 9 feet of water in his home. He is apparently in a two story home and is safe. He said the water came up very very fast.

Mr Beshel is live on FOX

http://www.fox8live.com/category/235642/watch-fox 8live


mississippi river levee? wow
Member Since: September 18, 2010 Posts: 0 Comments: 4576
Quoting odinslightning:
i dunno if i agree w/ the NHC calling this moving 8 mph....i think they are measuring the distance from where to where? you can throw a dart at 1/2 of a degree to the left, right, up, or down, and call that the center....but watch the wv loop....it certainly looks stalled to me....

http://www.goes.noaa.gov/HURRLOOPS/gulfwv.html

Link


Remember they are using long-term motion, and in the last 6 hours Isaac has moved about 45 miles, which is 7.5 mph. The last 3 hours he hasn't moved much of that 45 miles though.
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Im in Houma can someone tell me the direction on the wind I'm getting right now . Been up too long can't think.
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i think isaac likes the swamp better than the gulf.hes dropped 3-4mb last few hours and eyewall trying to recover...i wonder how hot the swamp water is?
Member Since: September 18, 2010 Posts: 0 Comments: 4576
Quoting HurricaneHunterJoe:
are there many homes in braithwaite LA?


No. This is a known weak spot in the levee. It failed in Gustav (and of course in Katrina).

https://maps.google.com/maps?q=Braithwaite,+LA&hl =en&ll=29.859553,-89.935369&spn=0.038409,0.0739&sl l=29.5333,-89.1&sspn=0.616548,1.182404&oq=Brait&hn ear=Braithwaite,+Plaquemines,+Louisiana&t=h&z=14
Member Since: September 19, 2007 Posts: 0 Comments: 287
Don Beshel from Braithwaite is reporting that the water came over the levies and he now has 9 feet of water in his home. He is apparently in a two story home and is safe. He said the water came up very very fast.

Mr Beshel is live on FOX

http://www.fox8live.com/category/235642/watch-fox 8live
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i dunno if i agree w/ the NHC calling this moving 8 mph....i think they are measuring the distance from where to where? you can throw a dart at 1/2 of a degree to the left, right, up, or down, and call that the center....but watch the wv loop....it certainly looks stalled to me....

http://www.goes.noaa.gov/HURRLOOPS/gulfwv.html

Link


what i mean is that the former "eyewall" was just a large ring of storms around a large clearing....and now we are seeing an eyewall form as this slings part of it's size off and tightens up in the center....

the mb measurements and measured wind speed at a given moment may be higher or lower by .2 degrees whichever direction because its tightening up from a large circumference....
Member Since: September 3, 2009 Posts: 0 Comments: 475
looks like swampfall#2 and pressure dropping,eyewall trying to close off
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Quoting jake436:
It's not their fault...they can't possibly understand without seeing it for themselves. Just want people to realize the difference between LA and the surrounding states' topography. It's just different in LA. There isn't anywhere else around with the marsh system we have, and if they're familiar with TX marsh or MS/AL marsh or FL marsh, they think it's the same here. It's not. It's that multiplied by 100,000. The marsh doesn't end a few hundred yds from the Gulf here. It ends 100 MILES from the coast. One thing to draw a comparison to would be the Everglades in FL. Remember Katrina and Andrew both sustained or even gained strength crossing there. It's because there's not much land there. Same here, but even moreso. That's a joke, right? Chalmette received over 4" of rain between midnight and 2 am.


They are probably looking at the cumulative storm radar which shows much lighter rain. Just judging from the puddle I walked through to reset a breaker we've had much higher rain totals in several of the major afternoon thunder boomers in the past month.
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1120. zillaTX
done no, able to make another move...questionable thoughts?
Member Since: July 28, 2011 Posts: 0 Comments: 50
000
URNT12 KNHC 290802
VORTEX DATA MESSAGE AL092012
A. 29/07:27:40Z
B. 29 deg 09 min N
090 deg 22 min W
C. 700 mb 2843 m
D. 55 kt
E. 249 deg 13 nm
F. 354 deg 62 kt
G. 256 deg 16 nm
H. 969 mb
I. 12 C / 3046 m
J. 17 C / 3044 m
K. 8 C / NA
L. OPEN W
M. C50

N. 12345 / 07
O. 0.02 / 0.5 nm
P. AF307 3409A ISAAC OB 05
MAX OUTBOUND AND MAX FL WIND 78 KT SE QUAD 07:48:10Z

Minimum 700 mb height decreased by 43 meters, a pretty big drop in 2 hours, but a 1 mb pressure increase? Interesting..
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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.