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 Felix2007:
So neither Isaac nor Kirk will be the big bad wolf of the hurricane season, but Leslie will??? Doesn't sound like a very threatening name.
Well Katrina didnt sound so formidable as a name either did it?
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Quoting TropicalAnalystwx13:

Thank god it didn't have that attitude when it moved off the coast of Cuba.

We could be talking about another Katrina, Isaac is still bad though.
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omg...jimbo just says "size matters" on the air.
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Quoting 1900hurricane:

Yeah, it looks to me he has taken at least a little sip of it, just enough to halt intensification or weaken him a little bit, but his eyewall is still (mostly) intact, and it wouldn't surprise me to see him mix it out fairly soon. Dry air is going to be looming though from here on out with a good portion of Isaac's circulation over land.


Yeah, that makes sense. It'll be interesting to see what will happen. I'm sure the folks going through this are hoping for a break of any kind.
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Quoting CybrTeddy:
Via Grand Isle Mayor: Island has significant damage and water on the island is waist deep

Bad News...
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Rain and wind has picked up again and from the looks on radar will be here for awhile. Guess it was about time - lol
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Quoting DavidHOUTX:


LOL This is completely slacking. NOLA current conditions... SNOW???



I remember seeing some weather station in NE Texas report something like 105 degrees with blowing snow during the summer.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Please refrain from talking about kirk fplease
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Quoting HopquickSteve:
"Hurricane Isaac is ashore over Southeast Louisiana..."

*was ashore.


Those maps under the radar are VERY deceiving. That's not 'land'. That finger of 'land' that it crossed when they called 'landfall' is Southwest Pass. SW Pass is literally rip rap and water hyacinths. That's it. There's no 'land' there.
Amazingly, even the met in NOLA on WWL reported it as landfall, of course parroting the NHC. But he took it a step further that he should know better than to do. He said it would start weakening now that it's made 'landfall'. And he's been a met there for 20+ years. Poor reporting. At landfall, I usually try to watch local news, because you SHOULD be able to get info from someone that SHOULD know the local terrain/area. Apparently Mr. Arredondo does not. Of course it's back over water now. It never WAS over land.
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Quoting Diabellical:
IN NOLA:

power still up
midcity orleans/bayou st. John
70119

992.8mb



That's good news
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Shell Beach water level:
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Thanks Dr. Masters
...DEPRESSION UPGRADED TO A TROPICAL STORM...
11:00 PM AST Tue Aug 28
Location: 23.9°N 45.0°W
Moving: W at 12 mph
Min pressure: 1007 mb
Max sustained: 45 mph
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Quoting ProgressivePulse:
Weakening may be short lived. Isaac shut out that dry air pretty quick and is continuing to close off.


Thank god it didn't have that attitude when it moved off the coast of Cuba.
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Via Grand Isle Mayor: Island has significant damage and water on the island is waist deep
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things are picking up here in Mobile and looks like the rain has settled in for awhile..
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So neither Isaac nor Kirk will be the big bad wolf of the hurricane season, but Leslie will??? Doesn't sound like a very threatening name.
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Link

not good
Member Since: July 10, 2005 Posts: 3 Comments: 1279
Quoting TropicalAnalystwx13:
Thanks Dr. Masters.

Dang...somebody's slacking tonight.



LOL This is completely slacking. NOLA current conditions... SNOW???

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Does look to be moving again. Possible second landfall on Grand Isle overnight.
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Thanks again Dr. Masters.
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Dr. Masters was just on The Weather Channel again! :)
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Quoting Tazmanian:
Hmmm how can dr m be at TWC and updated his blog at the same time

Taz, remember? TWC bought Weather Underground.
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Weakening may be short lived. Isaac shut out that dry air pretty quick and is continuing to close off.

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The prediction was that Issac would slow down after landfall. But it seems that it didn't quite get inland before that happened.

Is the thinking on track of Issac basically unchanged? Or is the blocking high looking like it will significantly change the track?
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Thanks Dr. M!
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Quoting Tazmanian:
Hmmm how can dr m be at TWC and updated his blog at the same time


from his laptop or use of one of the TWC computers
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Still possible?



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http://www.nhc.noaa.gov/

TS Kirk?
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Quoting mcmurray02:
Checking the various satellite and radar presentations, it looks as if some dry air has made some quick integration into the center (or near it.)

Yeah, it looks to me he has taken at least a little sip of it, just enough to halt intensification or weaken him a little bit, but his eyewall is still (mostly) intact, and it wouldn't surprise me to see him mix it out fairly soon. Dry air is going to be looming though from here on out with a good portion of Isaac's circulation over land.
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Jeff back on TWC
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BULLETIN
TROPICAL STORM KIRK ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
1100 PM AST TUE AUG 28 2012

...DEPRESSION UPGRADED TO A TROPICAL STORM...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...23.9N 45.0W
ABOUT 1230 MI...1980 KM ENE OF THE NORTHERN LEEWARD ISLANDS
ABOUT 1440 MI...2315 KM SW OF THE AZORES
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


WATCHES AND WARNINGS
--------------------
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM KIRK WAS
LOCATED NEAR LATITUDE 23.9 NORTH...LONGITUDE 45.0 WEST. KIRK IS
MOVING TOWARD THE WEST NEAR 12 MPH...19 KM/H...AND THIS MOTION IS
EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS. A TURN TOWARD THE WEST-
NORTHWEST IS FORECAST BY LATE WEDNESDAY.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 45 MPH...75 KM/H...
WITH HIGHER GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT
48 HOURS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 80 MILES...130 KM
TO THE NORTH OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB...29.74 INCHES.


HAZARDS AFFECTING LAND
----------------------
NONE


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM AST.

$$
FORECASTER KIMBERLAIN
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Quoting TropicalAnalystwx13:
TROPICAL STORM KIRK FORECAST/ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
0300 UTC WED AUG 29 2012

THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.

TROPICAL STORM CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
POSITION ACCURATE WITHIN 30 NM

PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB
MAX SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT.
34 KT....... 70NE 0SE 0SW 50NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
AT 29/0000Z CENTER WAS LOCATED NEAR 23.8N 44.5W

FORECAST VALID 29/1200Z 24.2N 46.6W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 0SE 0SW 40NW.

FORECAST VALID 30/0000Z 24.5N 48.6W
MAX WIND 50 KT...GUSTS 60 KT.
34 KT... 70NE 30SE 0SW 50NW.

FORECAST VALID 30/1200Z 25.0N 50.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 31/0000Z 26.0N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 01/0000Z 29.0N 55.3W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 50SE 30SW 60NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 175 NM
ON DAY 4 AND 225 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 02/0000Z 34.8N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.

OUTLOOK VALID 03/0000Z 42.3N 44.9W
MAX WIND 55 KT...GUSTS 65 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 23.9N 45.0W

NEXT ADVISORY AT 29/0900Z

$$
FORECASTER KIMBERLAIN/CANGIALOSI


The NHC suddenly became much more peachy on Kirk's future.
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...DEPRESSION UPGRADED TO A TROPICAL STORM...
11:00 PM AST Tue Aug 28
Location: 23.9°N 45.0°W
Moving: W at 12 mph
Min pressure: 1007 mb
Max sustained: 45 mph
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I'm watching Dr. Masters on TWC right now. Busy man. :)
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Kirk is on the NOAA website
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Hmmm how can dr m be at TWC and updated his blog at the same time
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2nd lanfall into grand isle then on to houma




thanks for update doc
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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.

whew...

A night to remember
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TROPICAL STORM KIRK FORECAST/ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
0300 UTC WED AUG 29 2012

THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.

TROPICAL STORM CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
POSITION ACCURATE WITHIN 30 NM

PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB
MAX SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT.
34 KT....... 70NE 0SE 0SW 50NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 23.9N 45.0W AT 29/0300Z
AT 29/0000Z CENTER WAS LOCATED NEAR 23.8N 44.5W

FORECAST VALID 29/1200Z 24.2N 46.6W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 0SE 0SW 40NW.

FORECAST VALID 30/0000Z 24.5N 48.6W
MAX WIND 50 KT...GUSTS 60 KT.
34 KT... 70NE 30SE 0SW 50NW.

FORECAST VALID 30/1200Z 25.0N 50.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 31/0000Z 26.0N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 40SE 20SW 60NW.

FORECAST VALID 01/0000Z 29.0N 55.3W
MAX WIND 55 KT...GUSTS 65 KT.
34 KT... 70NE 50SE 30SW 60NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 175 NM
ON DAY 4 AND 225 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 02/0000Z 34.8N 52.9W
MAX WIND 55 KT...GUSTS 65 KT.

OUTLOOK VALID 03/0000Z 42.3N 44.9W
MAX WIND 55 KT...GUSTS 65 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 23.9N 45.0W

NEXT ADVISORY AT 29/0900Z

$$
FORECASTER KIMBERLAIN/CANGIALOSI
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IN NOLA:

power still up
midcity orleans/bayou st. John
70119

992.8mb

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I thought they would,for cover,cuz if they didn't and it ends up in Texas,they would look bad.
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Quoting TropicalAnalystwx13:
Thanks Dr. Masters.

Dang...somebody's slacking tonight.



They show a small patch of either ts watch or ts winds in Texas there.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Thanks, Dr. Masters.

This is a very serious storm. I hope the levees hold.
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Quoting TomTaylor:
Latest Rapid Scan Loop over Isaac shows that cloud tops have warmed rather significantly over the last hour (although there is about a 45 minute gap in coverage). The latest recon pass showed that Isaac's intensity has leveled off and Isaac may have slightly weakened since then (although we'd need recon to confirm this) based off satellite imagery showing the cloud tops continue to warm over the center.

Latest SRSO GOES-14 Image (click for loop!)



Hey Tom but still in the water is a big problem any way
Member Since: June 20, 2012 Posts: 0 Comments: 2159
Quoting GTcooliebai:
Hey Dr. Masters do you see any chance of upwelling from Isaac if he stalls out long enough?
There is no cooler water to upwell along the coast. The water is shallow and warm all the way to the bottom.
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Does anyone have an idea of the lowest pressure of any landfalling Category 1 in the Atlantic basin? I'm guessing Isaac should be up there within the top 10?
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Greetings. Good timing, this !

What a weirdo Isaac is and has been, all along.
Great storm !

But really, I'm hoping for minimal trouble for the people there.
Could get pretty nasty !
Stay safe, all.
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Thanks, Jeff !
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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.

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