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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:)
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Quoting wxchaser97:

He sure has been difficult and will continue to be.
Now I see who he takes after, that's Debby's brother.
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Quoting Momnick8BR:


Heard they were under water.


That makes me want to type a sadface...but I'll refrain on the blog...
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Quoting TexNowNM:


You remember well, actually. Over 40 killed and unbelievable damage. It just sat there, half on land and half over the Gulf just sucking up water to dump out as rain. Some even said it didn't strictly qualify as a tropical storm due to the questionable closed circulation. There were multiple counties under disaster declaration. It just rained for ever!

Oh, wow, I did not know it killed that many people. More than the vast majority of hurricanes ever do, I think.

I didn't remember the designation controversy, either, but I do remember it just raining and raining.
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Quoting Momnick8BR:


Heard they were under water.




They soon will be if they aren't now.


Storm tot should be up to a foot by morning if current rates keep up.
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Wasn't there a model a couple of days ago that stalled it out over south Louisiana.... I know that I didnt dream that
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Quoting greene47:
I wonder what the fate of Grand Isle is


Heard they were under water.
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Quoting GTcooliebai:
It sure does he has been one tough sun of a gun to track and a head scratcher even for the experts.

He sure has been difficult and will continue to be.
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Tornado Warning


ORNADO WARNING
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

$$
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Looks like Isaac is all but settled in here as a basic landfalling TS. He did good work to match the records of the big kitty Kat 7 years ago and after coming up a few hours short he has headed of to a different story.

Catch you all in a few weeks for the next special event!
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Quoting tennisgirl08:


Things are getting creepy here. Clouds are moving extremely fast and tornado sirens loud as ever. VERY gusty winds!

Stay safe then, got to be a sight to see.
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Quoting tennisgirl08:


Things are getting creepy here. Clouds are moving extremely fast and tornado sirens loud as ever. VERY gusty winds!
It sounds like the winds are finally working there way down.
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Will Isaac be retired?
A) Yes
B) No
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With that ridge building back again, im expecting a continue west or WSW movement
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Quoting GTcooliebai:
Isaac looking a little ragged, but don't let this appearance fool you as storm surge and flooding remain the primary threats.


He is still a major threat and he could easily bounce back.
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Quoting tennisgirl08:


Things are getting creepy here. Clouds are moving extremely fast and tornado sirens loud as ever. VERY gusty winds!


Stay safe!
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REPOST
(click to enlarge)

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Quoting wxchaser97:
Tornado warning in Mobile, take shelter.


Things are getting creepy here. Clouds are moving extremely fast and tornado sirens loud as ever. VERY gusty winds!
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HURRICANE ISAAC FORECAST/ADVISORY NUMBER 32
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
0300 UTC WED AUG 29 2012

CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

THE TROPICAL STORM WATCH FROM WEST OF CAMERON LOUISIANA TO SABINE
PASS TEXAS HAS BEEN REPLACED WITH A TROPICAL STORM WARNING.

...

HURRICANE CENTER LOCATED NEAR 29.0N 89.7W AT 29/0300Z
POSITION ACCURATE WITHIN 15 NM

PRESENT MOVEMENT TOWARD THE NORTHWEST OR 310 DEGREES AT 7 KT
Member Since: September 19, 2007 Posts: 0 Comments: 287
Quoting GTcooliebai:
Isaac looking a little ragged, but don't let this appearance fool you as storm surge and flooding remain the primary threats.



It could easily flare back up in short order.
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Extrapolated surface pressures from the last recon pass bottomed out at 969.6

055530 2901N 08955W 8428 01234 9696 +212 +206 104009 015 004 003 03
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Quoting wxchaser97:
The definition of the name Isaac is he who laughs. That fits so well with this storm.
...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
It sure does he has been one tough sun of a gun to track and a head scratcher even for the experts.
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Quoting DataNerd:




With that setup may get shoved back out into the gulf.


Ridge is building back in it seems and/or new trough approaching.


Going to be a mess for the next 5 days easily.

Could this continue west??
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No rain here in Baton Rouge, just gusts in the 30s. Most of us have power, though most of NOLA is without. My brother's near the Garden District went out around 9:30 Central time.
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I wonder what the fate of Grand Isle is
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Quoting sunlinepr:
Very strange surroundings... looks like he can go either way... E or W
But dry air is all around.... specially now on the North...






With that setup may get shoved back out into the gulf.


Ridge is building back in it seems and/or new trough approaching.


Going to be a mess for the next 5 days easily.
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Quoting LeopardMoth:

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.


You remember well, actually. Over 40 killed and unbelievable damage. It just sat there, half on land and half over the Gulf just sucking up water to dump out as rain. Some even said it didn't strictly qualify as a tropical storm due to the questionable closed circulation. There were multiple counties under disaster declaration. It just rained for ever!
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Looks like he's wobbling north again. Might not last. He needs to hurry up and spread the rain across the areas that really need it.
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Isaac looking a little ragged, but don't let this appearance fool you as storm surge and flooding remain the primary threats.

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I wouldn't look for any track changes coming up from this wording. But I could be wrong. It has happened. :)

HURRICANE ISAAC TROPICAL CYCLONE POSITION ESTIMATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
100 AM CDT WED AUG 29 2012

...CENTER OF ISAAC STILL OVER WATER...

AT 100 AM CDT...0600 UTC...THE CENTER OF HURRICANE ISAAC WAS
ESTIMATED NEAR LATITUDE 29.0 NORTH...LONGITUDE 90.0 WEST...OR ABOUT
60 MILES SOUTHEAST OF HOUMA LOUISIANA...AND ABOUT 70 MILES SOUTH OF
NEW ORLEANS LOUISIANA. ISAAC HAS MOVED LITTLE OVER THE PAST COUPLE
OF HOURS...BUT A SLOW NORTHWESTWARD MOTION IS EXPECTED TO RESUME
LATER THIS MORNING.

A SUSTAINED WIND OF 62 MPH WITH A GUST TO 71 MPH WAS RECENTLY
REPORTED AT SHELL BEACH LOUISIANA. A SUSTAINED WIND OF 57 MPH WITH
A GUST TO 79 MPH WAS REPORTED WITHIN THE PAST HOUR AT PILOTTOWN
LOUISIANA. A SUSTAINED WIND OF 54 MPH WITH A GUST TO 68 MPH WAS
REPORTED AT NEW CANAL STATION IN NEW ORLEANS. A WIND GUST TO 80
MPH WAS REPORTED BY A HAM RADIO OPERATOR AT ALGIERS IN JEFFERSON
PARISH LOUISIANA.

A STORM SURGE OF 4.3 FEET WAS RECENTLY REPORTED AT A NATIONAL OCEAN
SERVICE TIDE GAUGE AT NEW CANAL STATION ON THE SOUTH SHORE OF LAKE
PONTCHARTRAIN.
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Quoting WaterWitch11:


here kitty kitty. oh sorry i mean here puppy puppy.


oh well if that isn't creepy i don't know what is.
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Quoting GTcooliebai:
The 12-17 named storms that the NOAA released on Aug. 9 doesn't seem too far off now. I'm actually going to up my numbers to 18/9/3

Since I only started posting in July I didn't make an early season prediction. Now I have to say 16/8/2.
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(click to enlarge)

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Quoting sarahjola:
no i don't and i want to thank you for answering my questions. i have 2 girls and i am getting a bit nrevous. so thanks! :)
You're welcome. I know the weather can get scary, especially at night.

All right then - the radar. Search for Mandeville, LA in the search box at the top of any wu page. When you get the forecast page, page down and you'll see a small radar box. Click on the "nexrad" option inside the radar box. (On classic wu, just click the box.) You will have local radar with a little "x" on it for Mandeville's location. Look and you'll see many options. Find and click the animate option and you can see the storm rain bands that might be moving toward you. These bands show rain but the wind may be stronger in these bands also. The wu radar updates by itself and will stay current. You shouldn't have to refresh. That is the simplest way to keep up with what might be coming. It's looking like SE LA will be getting a lot of rain and wind in the coming hours.

Also listen to your media people and local authorities for any updates on the situation. If your power goes out, well, I hope you got a battery radio and/or a NOAA weather radio, but if you don't, just hunker in for the duration. The emergency management folks in NOLA and LA have their acts together. You'll be okay.
:)
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Joyce = Fish.

Kirk = Fish

Now Lesli will also be a fish???!!!

Meanwhile we in the Leewards are experiencing drought conditions again!! August have been dry! Everything fell on island south of Guadeloupe.

WTF!
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Very strange surroundings... looks like he can go either way... E or W
But dry air is all around.... specially now on the North...


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The definition of the name Isaac is he who laughs. That fits so well with this storm.
...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
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Quoting STXHurricanes2012:
Not good...stationary now!!


This means a strom that will start falling apart and winds will subside. However, rains will only increase for areas currently getting rain. This also means that the storm is more likely to move in a north eastward direction eventually and less help the the drought areas.
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The following just went up, relayed from NWS NOLA

FLASH FLOOD WARNING
LAC051-071-075-087-089-290845-
/O.NEW.KLIX.FF.W.0050.120829T0557Z-120829T0845Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000 Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1257 AM CDT WED AUG 29 2012

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* FLASH FLOOD WARNING FOR...
JEFFERSON PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...TIMBERLANE...METAIRIE...MARRERO...
KENNER...HARVEY...AVONDALE...
ORLEANS PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...NEW ORLEANS...EAST NEW ORLEANS...
NORTHWESTERN PLAQUEMINES PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...PORT SULPHUR...BELLE CHASSE...
WESTERN ST. BERNARD PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF CHALMETTE...
ST. CHARLES PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITY OF HAHNVILLE...

* UNTIL 345 AM CDT

* AT 1248 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS
DETECTED FLASH FLOODING IS LIKELY FROM PERSISTENT TROPICAL
RAINBANDS FROM HURRICANE ISAAC ACROSS THE SOUTHSHORE AREAS OF
METROPOLITAN NEW ORLEANS...AND COASTAL AREAS TO THE EAST AND
SOUTHEAST.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF
CANALS...HIGHWAYS...UNDERPASSES...AND POOR DRAINAGE AREAS. DRAINAGE
LIMITATIONS BECAUSE OF GATE CLOSURES AND VERY HIGH STORM TIDES WILL
AUGMENT THE FLASH FLOOD POTENTIAL DURING PERSISTENT HEAVY RAIN.

A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING.
IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY.
RESIDENTS LIVING IN AREAS SUBJECTED TO FLOODING SHOULD TAKE
IMMEDIATE PRECAUTIONS TO PROTECT LIFE AND PROPERTY. DO NOT ATTEMPT
TO CROSS SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN DEPTH BY FOOT
OR BY AUTOMOBILE.

&&

LAT...LON 2950 9010 2967 9016 2980 9044 3002 9054
3007 9038 3003 9011 3014 8972 3003 8971
3004 8981 2995 8984 2997 8973 2989 8959
2963 8948 2965 8963 2959 8971 2946 8951
2939 8951 2938 8936 2931 8953

$$

22/TD
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Well Texas u can breathe easy. The storm is now stationary no ,ore western component to it. When it ramps up again should have a north or north north west direction before the recurve.. Sleep easy texas
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That eyewall is looking pretty raggedy but it doesn't look on radar likes its moved hardly at all in the last hour (at least not the east side) and the feeder bands on the east don't show any sign of letting up. Slidell radar only shows about 2.5" of rain in the metro area, and the winds are not what they were two hours ago. At these rainfall rates we've see worse at least one afternoon a week for the last month.

Still, if it camps where it is long enough and the feeder bands keep coming through with just enough winds to keep the trucks in there's going to be some very unhappy utility customers.

My poplarnemometers are about Force 6 at worst and the airport is reporting winds around 38-43, down from sustained 50 earlier.
Member Since: September 19, 2007 Posts: 0 Comments: 287
Quoting Jay5711:


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,
..

Keep us posted, we appreciate it.
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Winds about steady as they were.


Good eye returns on radar:

Link
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ON THE FORECAST
TRACK...THE CENTER OF ISAAC WILL CONTINUE MOVING NEAR OR OVER THE
SOUTHEASTERN COAST OF LOUISIANA THIS MORNING...AND MOVE INLAND OVER
SOUTHEASTERN LOUISIANA DURING THE NEXT DAY OR SO.

Isaac is still laughing...
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Quoting wxchaser97:

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.
The 12-17 named storms that the NOAA released on Aug. 9 doesn't seem too far off now. I'm actually going to up my numbers to 18/9/3
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NHC says 'stationary'
969mb
80mph
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Quoting deepee:


are you flirting with me on dr. m's blog?


here kitty kitty. oh sorry i mean here puppy puppy.
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Tornado warning in Mobile, take shelter.
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Rainfall going to be an issue for the next 48 hrs in NOLA however, storm should resume NW course (we hope) and eventually get moving out of there.


Turn to the west and stall would result in rain problems for all of SE Texas and Houston as well as the circulation begins to open up.

If the stall was long enough, it could present an opportunity for interaction with a trough next week.


Hopefully, no stall occurs. I don't expect one to.
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Quoting xtremeweathertracker:


Hmmm i live in Buna too! LOL


Good! No storm surge up there! South of I10 it is always an issue.
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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
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About JeffMasters

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