Hurricane Isaac hits Louisiana, driving dangerous storm surges

By: Dr. Jeff Masters , 2:27 AM GMT on August 29, 2012

Share this Blog
53
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 919 - 869

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44Blog Index

Quoting Felix2007:

Can you please explain this map to me? I don't understand it.


lines green and blue are the forecast Red line is the the path ,The Quadrants are the Regions
Member Since: Posts: Comments:
Quoting GPTGUY:
1am advisory has Isaac stationary!

Where did you find this? I don't see any 1 am advisory.
Member Since: Posts: Comments:
Not good...stationary now!!
Member Since: Posts: Comments:
it is literally up in the air. With what I'm seeing on radar with the storm moving west to southwest, I suggest you ratchet your preparations up. This is too close and I am not sure if it will make the turn the NHC is forecasting, but By late tomorrow evening (Wednesday Evening), we could very well have sustained tropical storm force winds which we can handle - it's the possible hurricane force winds I'm becoming increasingly concerned about. KBMT 12
Member Since: Posts: Comments:
.CENTER OF ISAAC STILL OVER WATER... ...U.S. Warnings in Effect...
1:00 AM CDT Wed Aug 29
Location: 29.0°N 90.0°W
Moving: Stationary
Min pressure: 969 mb
Max sustained: 80 mph
Member Since: Posts: Comments:
Quoting GPTGUY:
1am advisory has Isaac stationary!


Guess this is where it starts back to the NW motion. I assume...
Member Since: Posts: Comments:
Quoting zillaTX:


Eh???


ehh yes...looking pretty rough....
Member Since: Posts: Comments:
If Leslie forms before September 1 it'll be the 3rd earliest L storm.
Member Since: Posts: Comments:
Quoting WaterWitch11:


i bet you are just as nice in person


are you flirting with me on dr. m's blog?
Member Since: Posts: Comments:
Similar to the last two, overnights are not Isaac's friend. Once again he's taking in some dry air and it looks like his eyewall has collapsed. It won't take much to downgrade back to tropical storm status.

He'll keep spinning wind, rain, and storm surge though.

Hopefully he'll get to moving NW
Member Since: Posts: Comments:
000
WFUS54 KMOB 290549
TORMOB
ALC003-097-290645-
/O.NEW.KMOB.TO.W.0038.120829T0549Z-120829T0645Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE MOBILE AL
1249 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN MOBILE HAS ISSUED A

* TORNADO WARNING FOR...
WEST CENTRAL BALDWIN COUNTY IN SOUTHWEST ALABAMA...
NORTHERN MOBILE COUNTY IN SOUTHWEST ALABAMA...

* UNTIL 145 AM CDT

* AT 1246 AM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A
TORNADO WAS LOCATED 4 MILES SOUTHWEST OF ROBERTSDALE...OR 3 MILES
WEST OF SUMMERDALE...MOVING NORTHWEST AT 50 MPH.

* LOCATIONS IMPACTED INCLUDE...
DOWNTOWN MOBILE... MOVICO... SATSUMA...
SARALAND... PRICHARD... MOUNT VERNON...
I65 AND US 45... I65 AND US 43... I65 AND I165...

THIS INCLUDES INTERSTATE 10 BETWEEN MILE MARKERS 24 AND 46. THIS
INCLUDES INTERSTATE 65 BETWEEN MILE MARKERS 5 AND 30.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A TORNADO WATCH REMAINS IN EFFECT UNTIL 700 AM CDT WEDNESDAY MORNING
FOR SOUTHWESTERN ALABAMA AND NORTHWEST FLORIDA AND SOUTHEAST
MISSISSIPPI.

&&

LAT...LON 3054 8791 3062 8792 3066 8795 3067 8801
3064 8803 3064 8805 3090 8841 3113 8798
3053 8766 3043 8776
TIME...MOT...LOC 0549Z 135DEG 43KT 3053 8777

$$
Member Since: Posts: Comments:
Quoting xtremeweathertracker:


Hmmm i live in Buna too! LOL


Well howdy neighbor!!
Member Since: Posts: Comments:
1am advisory has Isaac stationary!
Member Since: Posts: Comments:
Quoting sarahjola:
myrtle grove just reported gust of 110 mph. heard it on channel 8 news


Did a cow fly by as well? Maybe I am thinking about the twister attraction at universal?
Member Since: Posts: Comments:
Quoting TexNowNM:

It's a troubling situation.


Sounds like Allison in Texas.

I think I remember Allison... that's the one that didn't make it past Tropical Storm strength, but it did a boatload of damage. It just sat there spinning and dumping massive amounts of rain. Did it keep its COC just offshore for a long time? I didn't live there, so it's hard to remember.
Member Since: Posts: Comments:
Quoting deepee:


i was actually following it earlier. i'm exaggerating now. but still, good story to tell for the rest of his life!


i bet you are just as nice in person
Member Since: Posts: Comments:
903. etxwx
Quoting TomTaylor:
I'd refer to the NWS, or perhaps more specifically, the HPC for official forecasts...

Thanks Tom, I definitely will do that...looks rain is in the forecast and hopefully that's all. I was just teasing Levi. Had encounters with Rita and Ike - and that was enough for me.
G'nite all...hope everyone stays safe!
Member Since: Posts: Comments:

KBMT 12 News HD Isaac is wobbling southwest. It appears that the storm is farther south than the National Hurricane Center Cone of Uncertainty as of this writing. However, a turn is forecasted...the question is WHEN? Will it begin turning northwards around Morgan City or wait until Lake Charles or not turn at all and be a coastal raker? Every hour that goes by and the storm does not turn, the chances of tropical storm force winds (possibly worse) increase in Southeast Texas. At this pace without a turn, late Wednesday Evening sustained tropical storm force winds could be in Southeast Texas - that's 24 hours from now.
Member Since: Posts: Comments:
Quoting CCkid00:
this hurricane is soooooooo slow. denham springs, la. here, about 10 miles east of BR. winds picked up at daylight this morning (well, actually Tuesday morning). they have been probably 25-30 all evening and night, with gusts to 35. just a sprinkle of rain earlier. strange storm.


In Denham too! Strange is an understatement.
Member Since: Posts: Comments:
Quoting wxchaser97:
You're welcome, it is nice to get ground truth reports from the areas being impacted.


I'm located above vermillion bay in Iberia parish. Been through every storm that hit in this area since I can remember.. Andrew was the worse for me.. As of noe the wind is about 30 mph gusting to 40.. No rain as of yet,
..
Member Since: Posts: Comments:
myrtle grove just reported gust of 110 mph. heard it on channel 8 news
Member Since: Posts: Comments:
Quoting tomas5tex:


I live in Buna. Better to stock now and not need it than wait IMO.


Hmmm i live in Buna too! LOL
Member Since: Posts: Comments:
Quoting GTcooliebai:
That makes sense because after 98L there is another storm showing up in the long range on the GFS coming off Africa and after that the CFS has 2 more waves rolling off Africa and 2 systems in the GOM forming off trough splits and tail ends of fronts.

If 98L forms into a TS before the end of the month then we tie the record for the most storms in August. It has been very active lately. The activity should continue with an active September.
Member Since: Posts: Comments:
Quoting weatherganny:

Thank you for posting that... I had been looking for info and couldnt find any..I guess we are doing the watch and wait thing... I truly hope all of those under the gun now are safe.


If you go to facebook and like KBMT 12 you will get his updates...I do the same for KFDM and Fox 4
Member Since: Posts: Comments:
Quoting AtHomeInTX:


Did you see his comments on Facebook? Put the station call letters in search. Pretty interesting.


Thanks for the info... :)
Member Since: Posts: Comments:
Isaac looks like a big sigh for the oil rigs and refineries as there appear to be no crippling affects from this storm other than a forced vacation for a few days for rig workers....so far
Member Since: Posts: Comments:

It's a troubling situation.


Sounds like Allison in Texas.
Member Since: Posts: Comments:
Quoting SETXborda:
In Bridge City, when should I go stock up? Maybe if it gets as far as Morgan City?


I live in Buna. Better to stock now and not need it than wait IMO.
Member Since: Posts: Comments:
Quoting weatherganny:

Thank you for posting that... I had been looking for info and couldnt find any..I guess we are doing the watch and wait thing... I truly hope all of those under the gun now are safe.


Here is the NWS forecast for Bridge City, Tx....kinda gives you an idea of what to expect with the current NHC track! Guess it could be a little worse if Isaac decides to come further west.

Overnight A 20 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 78. North wind around 20 mph, with gusts as high as 25 mph.

Wednesday Tropical storm conditions possible. Scattered showers and thunderstorms, mainly before 1pm. Cloudy, with a high near 83. North wind 25 to 30 mph, with gusts as high as 35 mph. Chance of precipitation is 40%.

Wednesday Night Tropical storm conditions possible. Rain and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 77. North wind 25 to 30 mph becoming west 20 to 25 mph. Winds could gust as high as 35 mph. Chance of precipitation is 100%.

Thursday Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 80. Southwest wind around 15 mph, with gusts as high as 20 mph. Chance of precipitation is 100%.

Thursday Night Rain and possibly a thunderstorm. Low around 79. South wind 10 to 15 mph. Chance of precipitation is 80%.
Member Since: Posts: Comments:
Quoting GTcooliebai:
That makes sense because after 98L there is another storm showing up in the long range on the GFS coming off Africa and after that the CFS has 2 more waves rolling off Africa and 2 systems in the GOM forming off trough splits and tail ends of fronts.


Sigh...September...
Member Since: Posts: Comments:
889. ryang
Quoting CaribBoy:
Pre 98L nooo I need your rain!!! Don't turn north


Urrr...it is 98L lol
Member Since: Posts: Comments:
Quoting Jay5711:


Thanks, I've been lurking since before Katrina days, but decided to join since the storm is in our area and I may be able to give some insight to ppl about the current conditions..
You're welcome, it is nice to get ground truth reports from the areas being impacted.
Member Since: Posts: Comments:
Quoting TexasHurricane:
Channel 12 - SETX

"The next 12 hours will be crucial in the forecast for Southeast Texas. The storm is forecasted to gradually turn towards the northwest and then north. If it does not turn, or that turn is later than forecasted, then tropical storm force winds (or worse) could occur in Southeast Texas by Late Wednesday Night. The latest radar imagery actually shows a southwest movement the last hour or so. It is unclear if this is temporary.:


Did you see his comments on Facebook? Put the station call letters in search. Pretty interesting.
Member Since: Posts: Comments:
Quoting stormchaser19:
He wants to come again in september OH boy!!!!!!!
That makes sense because after 98L there is another storm showing up in the long range on the GFS coming off Africa and after that the CFS has 2 more waves rolling off Africa and 2 systems in the GOM forming off trough splits and tail ends of fronts.
Member Since: Posts: Comments:
Thanks to all giving info about SE Texas. Especially appreciate updates from local ABC and CBS affiliates.
Member Since: Posts: Comments:
Quoting stormchaser19:
He wants to come again in september OH boy!!!!!!!

Can you please explain this map to me? I don't understand it.
Member Since: Posts: Comments:
Quoting Bielle:

Good that you recognize the important stuff! :>)


i was actually following it earlier. i'm exaggerating now. but still, good story to tell for the rest of his life!
Member Since: Posts: Comments:
Pre 98L nooo I need your rain!!! Don't turn north
Member Since: October 6, 2007 Posts: 0 Comments: 6455
Quoting weatherganny:

Thank you for posting that... I had been looking for info and couldnt find any..I guess we are doing the watch and wait thing... I truly hope all of those under the gun now are safe.


Your welcome... :)
Member Since: Posts: Comments:
Interesting. Latest steering maps show the Bermuda high weakening a bit and backing off eastward. This becomes more evident if Isaac weakens a little.

What this will mean for Isaac track...idk??
Member Since: Posts: Comments:
Quoting TexasHurricane:
Channel 12 - SETX

"The next 12 hours will be crucial in the forecast for Southeast Texas. The storm is forecasted to gradually turn towards the northwest and then north. If it does not turn, or that turn is later than forecasted, then tropical storm force winds (or worse) could occur in Southeast Texas by Late Wednesday Night. The latest radar imagery actually shows a southwest movement the last hour or so. It is unclear if this is temporary.:

Thank you for posting that... I had been looking for info and couldnt find any..I guess we are doing the watch and wait thing... I truly hope all of those under the gun now are safe.
Member Since: Posts: Comments:
patrap! can i get one of the puppies? if it's the male i promise to name it Issac!
Member Since: Posts: Comments:
Quoting wxchaser97:

Isaac is just battering Louisiana and wont stop for a couple days, stay safe. Been good to see a lot of new people join over the past week due to Isaac.


Thanks, I've been lurking since before Katrina days, but decided to join since the storm is in our area and I may be able to give some insight to ppl about the current conditions..
Member Since: Posts: Comments:
Quoting etxwx:

As someone in extreme East Texas, I'm gonna hold you to that, Levi. ;-)
I'd refer to the NWS, or perhaps more specifically, the HPC for official forecasts...

Here's your forecasted rainfall from Isaac. You probably won't end up with as much as shown on this map, but there you have it

Member Since: Posts: Comments:
Quoting deepee:



STOP THE PRESSES.

I AM CURIOUS AS WELL.

THINK WE CAN GET THIS ON THE WEATHER CHANNEL?

SOMEONE CALL JEFF!

Good that you recognize the important stuff! :>)
Member Since: Posts: Comments:
Quoting sarahjola:
bet i get an answer to the "thanks for a major fail" comment, but nothing on the weather comments.


Well, I'm a lurker myself, but I find Isaac to be the most fascinating storm in a year of fascinating storms.

He is essentially, as has been mentioned before by other people who are regulars here, stuck.

He's strong enough to feel a trough and want to go poleward, but weak enough so that the ridge (that isn't deteriorating so much as it was supposed to) is powerful enough to not let it, so he keeps getting pulled north, and then forced back to the west. That's what I've seen. It's a complicated pattern, and I fear that Isaac will meander there and cause havoc until whenever such a pattern decides to let up.

Perhaps if he stays there and weakens enough due to upwelling and land interaction, he may go west, but he doesn't seem to want to weaken either, he's moving around enough, with such a large rotation, that he's getting all the warm water he can muster.

It's a troubling situation.
Member Since: Posts: Comments:
Quoting xtremeweathertracker:


2 pups so far..one male..one female!!


get this on the weather channel ASAP!
Member Since: Posts: Comments:
Check 845 sara
Member Since: Posts: Comments:
Quoting Bielle:
I've had to be AFK for several hours: did Patrap's puppies arrive safely?



STOP THE PRESSES.

I AM CURIOUS AS WELL.

THINK WE CAN GET THIS ON THE WEATHER CHANNEL?

SOMEONE CALL JEFF!
Member Since: Posts: Comments:
Quoting Bielle:
I've had to be AFK for several hours: did Patrap's puppies arrive safely?


indeed
Member Since: Posts: Comments:
Quoting TexasHurricane:
Channel 12 - SETX

"The next 12 hours will be crucial in the forecast for Southeast Texas. The storm is forecasted to gradually turn towards the northwest and then north. If it does not turn, or that turn is later than forecasted, then tropical storm force winds (or worse) could occur in Southeast Texas by Late Wednesday Night. The latest radar imagery actually shows a southwest movement the last hour or so. It is unclear if this is temporary.:


WOW figured they were asleep!! LOL
Member Since: Posts: Comments:

Viewing: 919 - 869

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44Blog Index

Top of Page

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.

Local Weather

Overcast
22 °F
Overcast

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron