Isaac pounding Louisiana, Mississippi, Alabama, and Florida

By: Dr. Jeff Masters , 4:01 PM GMT on August 29, 2012

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Hurricane Isaac continues to lumber slowly northwestwards at 6 mph, as it pounds Louisiana, Mississippi, Alabama, and Florida's Panhandle with torrential rains, high winds, and a damaging storm surge. The eye was partially over water for most of the 15 hours after Isaac's official landfall at 7:45 pm EDT Tuesday night, but New Orleans radar shows the eye of the storm is now fully ashore near Houma. The radar echoes show some weakening on the west side of the eyewall, where dry air has infiltrated the storm. Wind shear remains light, and upper level outflow over Isaac is as impressive as we've seen so far, with a strong outflow channel to the north, and a respectable one to the south, as well. Infrared and visible satellite loops show a very large, symmetric, and well organized storm, and Isaac is going to be able to stay near Category 1 hurricane strength all day today. This will allow Isaac to drop rainfall amounts of 15 - 20" in some areas of Louisiana before the storm is over. A few rainfall totals from Isaac through 11 am EDT:

9.26" New Orleans Lakefront Airport
5.59" Belle Chasse, LA
5.21" Mobile, AL
3.65" Hattiesburg, MS
3.42" Gulfport, MS
2.81" Biloxi, MS


Figure 1. Morning radar reflectivity image from New Orleans.

A dangerous storm surge event underway
Isaac is bringing a large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. Late this morning was high tide along much of the coast, and the highest water levels of Isaac are likely being experienced at many locations. At 11:30 am EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

8.0' Waveland, MS
8.2' Shell Beach, LA
2.0' Pensacola, FL
4.6' Pascagoula, MS
3.4' Mobile, AL

The peak 11.06' storm surge at 1:30 am EDT this morning at Shell Beach, which is in Lake Borgne, 20 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. In general, the storm surge heights from Isaac have been more characteristic of a strong Category 2 hurricane, rather than the weak Category 1 hurricane one might suppose Isaac is, based on its top sustained winds of 75 - 80 mph. The Saffir-Simpson Scale for ranking hurricanes is only a crude measure of their potential impacts.

A storm surge estimated at 12' moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. The surge continued upriver, elevating the water levels 10' in New Orleans (103 miles upstream from the mouth of the Mississippi), 8' in Baton Rouge (228 miles upstream), and 1.4' at Knox Landing, an amazing 314 miles upstream. The river was 7' low due to the great 2012 U.S. drought, and I suspect the near-record low flow rate of the river allowed the storm surge to propagate so far upstream. The salt water from the storm surge will be slow to leave the river, due to the continued winds of Isaac keeping the surge going, plus the very low flow rates of the river. One benefit of the heavy rains of 10 - 20 inches expected to fall over Louisiana over the next two days will be to increase the flow rate of the Mississippi River, helping flush the salt water out of the river. The low flow rates of the Mississippi had allowed salt water to move upriver to just south of New Orleans over the past few weeks, threatening the drinking water supply of Plaquemines Parish.


Figure 2. Tide gauge data from Waveland, Mississippi. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.) The storm tide at Waveland currently (9') is 2' higher than that of Category 2 Hurricane Gustav of 2008. Image credit: NOAA Tides and Currents.

Tropical Storm Kirk in the Central Atlantic
Tropical Storm Kirk formed Tuesday night in the Central Atlantic. Kirk's formation at 03 UTC on August 29 puts 2012 in 4th place for earliest formation date of the season's 11th storm. Only 2005, 1995, and 1933 had an earlier formation date of the season's 11th storm. Kirk should stay well out to sea and not trouble any land areas.


Figure 3. Morning satellite image of Tropical Storm Kirk.

Invest 98L in the Eastern Atlantic
A tropical wave (Invest 98L) is about 750 miles west-southwest of the Cape Verde Islands, and is moving west to west-northwest at about 15 mph. In their 8 am EDT Tropical Weather Outlook, NHC gave 98L a 50% chance of developing by Friday morning. Several of the models develop 98L into a tropical depression by this weekend, but none of the reliable models foresee that 98L will be a threat to the Lesser Antilles. The storm may be a threat to Bermuda next week, but it is too early to say if it may threaten the U.S.

Jeff Masters

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I was bored and decided to compare Aug 2004 with Aug 2012 (permitting formation of 98L!);

2012 has had all but one day where a functioning cyclone (or its remnants) existed, where 2004 had roughly five days. The way 2004 wins out though is through the power of the individual systems (3 majors, while we nearly made it with one [Gordon]).

Pretty rapid start to August!

P.S. Hurricane Alex (2004) also formed into a named system on 1st August. See any similarities in our current season, with exception of power of the systems as mentioned above.

Found it quite interesting is all.
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Quoting Tazmanian:
if you live in PR or the Lesser Antilles i would keep a vary close eye on 98L has some of the mode runs are start too point tours you




Thanks for the information. I only have access to sfwmd so i appreciate any info from other sources.
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Quoting floridaT:
i thought Jindal was for "smaller gov"


Everyone is until they need help. I'm not sure what else he expects the President to do right now. He already declared a disaster so the funds will be there. Till this thing stops blowing they can't move in rescue people.
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Quoting oracle28:


The cloud shield has reached Galveston Bay? How many miles is that from the center?


200+ miles
Member Since: July 14, 2008 Posts: 1 Comments: 9648
Quoting Tazmanian:
if you live in PR or the Lesser Antilles i would keep a vary close eye on 98L has some of the mode runs are start too point tours you



Thanks, Taz!
I've been watching that today.

Hoping it goes out to sea, but too early to know.....
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ugh, delete. Sorry for the dupe.
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Quoting sar2401:


Much of the water also came from the Lake, into Orleans, and then downstream to Plaquemines, which seems to be experiencing the worst flooding. There are many ways water gets into the rivers and canals in Orleans Parish than from coming straight in from the Gulf. It's the higher and stronger levees and floodwalls in areas where the water also comes in from the east that eventually ends up getting funneled to the south. This is not even counting the rainfall, which is also being sent south, since it's contained further north and can't spread out into the wetlands like it did before all the levee construction.

You obviously know a lot about New Orleans levee systems and drainage . Did you work for the USACE before 2005?
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Quoting doubtit:
CAT 5??



thats wish casting there but will see still a few days a way
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LESLIE
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As bad as this storm has been, imagine if it were a Category 3 or Category 4 like would have occurred if it built up a well-defined core several days before landfall. As it stands, the damage total will likely be over $2 billion.
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Quoting RitaEvac:
Looking east towards Galveston Bay, Isaac cloud shield closing in







The cloud shield has reached Galveston Bay? How many miles is that from the center?
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delete (dupe)
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Quoting Tazmanian:
if you live in PR or the Lesser Antilles i would keep a vary close eye on 98L has some of the mode runs are start too point tours you


CAT 5??
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Quoting GTcooliebai:
This is so sad...Guys this is from a Cat. 1 Hurricane, please leave if you know your area is flood prone.

Plaquemines levee breached.Cant personally authenticate,but very possible (via Carl Parker)

MT @JMLeblanc23 from 3 story Braithewaite home



That's terrible news to hear. It's freaky how this is the same exact day of Katrina.
Member Since: July 8, 2005 Posts: 259 Comments: 24478
Guys I have a question for you..

Did USA and the countries that can be affected by hurricanes like Mexico, Canada, Nicaragua, Costa Rica, Belize (UK), Azores etc. got into an agreement so that the NHC in Miami, FL USA is the sole authority to determine the status and tracking of any tropical cyclone in the Atlantic and Epac and no other country?

who can answer that?
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Quoting JasonRE:
Lafayette still not seeing rain. Wow......where is it?


You are in the west, or weaker side of the storm. Isaac as always had better outflow east. Now that he has bugun to weaken, the west outflow looks even more anemic. If he tracks more to the west when he finally gets moving, you may get some rain, but I think some showers are going to be about it for Lafayette,
Member Since: October 2, 2004 Posts: 0 Comments: 16302
Quoting geestar3:
I'm looking forward to finding out Isaac's impact on the "dead zone" (hypoxic area) of the Gulf Coast this year. The area (actually two smaller zones along the Louisiana coast)was quite small this year, because of the low flow of the Mississippi (the zone is driven by excessive nutrients that wash out of the river). It's possible that the storm will have mixed the waters of the zone enough to increase oxygen levels and reduce or even eliminate the zones.
http://www.treehugger.com/ocean-conservation/silv er-lining-gulf-mexicos-dead-zone-smaller-thanks-dr ought.html


I'm worried about the amount of oil from the Deep Horizon spill that will be stirred up by the storm.


There is more oil from people's garages in Plaquemines P. than from BP.
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Quoting HurricaneHunterJoe:
his eye looks to be improving and shrinking?

falling apart
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Quoting FOREX:


Sure looks like a fish storm. GFS says so anyway.


GFS said that about Isaac, then killed it off, then had it developing in the Caribbean and then all the drama we saw happened began. Euro doesn't even want to develop 98L. Euro seems to do the best with fully developed cyclones from what I've seen, as it has dropped a lot of storms this season.
Member Since: July 8, 2005 Posts: 259 Comments: 24478
read after ,me all 98L will not be a fish storm it is too early too tell where it is going
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Quoting CCkid00:
Denham Springs, La. here. about 10 miles due east of Baton Rouge. press conference about 30 minutes ago....they said the NWS is saying that very shortly we will begin experiencing combination tropical storm force/hurricane force winds and they will last until appx. 7 tomorrow morning. had a funnel cloud near our house early this morning. we still have power but has flickered since last night. heavy rain and near TS force winds, sustained now. wind started here yesterday morning with a breeze and we had TS gusts starting early last night. that is a lot of wind for a long time and saturated grounds. not a good mix with the trees. don't know which is worse....Gustav moving quickly through here, or this slow slow slow Isaac. gutters in subdivision were backed up very shortly after the rain started. never seen that here before, not even in Gustav. gonna be a long night.....


Hi CCkid, Alexandria, LA here. Still nothing here yet...but they say it should go downhill starting late tonight...
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Quoting redwagon:



What a stunning visual. I'll go read the write-up, because I'm willing to pay for this.


Don't need to it's completely free
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Quoting Grothar:
If some of you ever went back and re-read your blogs, you might be embarrassed. If not, there are enough of us who are already embarrassed for you.


As the old expression says.. its better to have someone think your a fool... then to make a statement that proves it ;)

Hows it going old timer :)
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Quoting USCGLT:
Notice the 70 MPH speed limit sign!!!

Meh, just a small puddle. These Michelins will plow right through that. lol
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I'm looking forward to finding out Isaac's impact on the "dead zone" (hypoxic area) of the Gulf Coast this year. The area (actually two smaller zones along the Louisiana coast)was quite small this year, because of the low flow of the Mississippi (the zone is driven by excessive nutrients that wash out of the river). It's possible that the storm will have mixed the waters of the zone enough to increase oxygen levels and reduce or even eliminate the zones.
http://www.treehugger.com/ocean-conservation/silv er-lining-gulf-mexicos-dead-zone-smaller-thanks-dr ought.html


I'm worried about the amount of oil from the Deep Horizon spill that will be stirred up by the storm.
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Quoting syn627:
I-10 near LaPlace, LA closed
Notice the 70 MPH speed limit sign!!!
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Quoting Tazmanian:
if you live in PR or the Lesser Antilles i would keep a vary close eye on 98L has some of the mode runs are start too point tours you




I have one eye taking a nap while the other one is watching....
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Quoting LAlurker:

Downstream? The water came from the Gulf.


Much of the water also came from the Lake, into Orleans, and then downstream to Plaquemines, which seems to be experiencing the worst flooding. There are many ways water gets into the rivers and canals in Orleans Parish than from coming straight in from the Gulf. It's the higher and stronger levees and floodwalls in areas where the water also comes in from the east that eventually ends up getting funneled to the south. This is not even counting the rainfall, which is also being sent south, since it's contained further north and can't spread out into the wetlands like it did before all the levee construction.
Member Since: October 2, 2004 Posts: 0 Comments: 16302
If some of you ever went back and re-read your blogs, you might be embarrassed. If not, there are enough of us who are already embarrassed for you.
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This is so sad...Guys this is from a Cat. 1 Hurricane, please leave if you know your area is flood prone.

Plaquemines levee breached.Cant personally authenticate,but very possible (via Carl Parker)

MT @JMLeblanc23 from 3 story Braithewaite home

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Quoting TropicalAnalystwx13:
Isaac may have had Category 1 winds, but the storm surge was that of a Category 3. Unbelievable pictures coming in.


Maybe this will jump- start the discussion about a more meaningful classification system.
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Quoting icmoore:


As has been asked by many today can't you guys wait to play the blame game after this disaster is over?


Not blaming any agency, neither government.... blaming personal decision, the ability to learn from the past....

Look in YTube for info, and you will see how many irresponsible videos of hurricane parties and nonsense.... while there is disaster around...
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finally saw dr. masters on TWC. awww...
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459. FOREX
Quoting Tazmanian:
98L is looking better and better evere sac

i have too say i think 98L is a TD now








we could be looking at TD 12 by 5am and am thinking 98L could be up too 70 too 80% at the next two


wow this is looking good 98L has in tell friday at 12am too make it too a name storm


The models are showing a fish storm right??
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I would say probably about a 75-80% chance that 98L recurves out to sea, probably even before Bermuda... We saw models shift west with Isaac, but I really don't see that happening with 98L... It's gonna be a great storm to just sit back and watch it strengthen... It will likely be a TD tomorrow if it keeps its current satellite appearance.

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Lafayette still not seeing rain. Wow......where is it?
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422. I'm thinking we will continue to see Isaac wobble slowly WNW for now, then hook up through LA probably clip maybe the east & the NE edge of TX, east side of OK may get a bit of rain, then move North up the west side of the MS River..leaving the moister east side to improve shipping, over MO and on to IL to kick off the fall planting season. I'm leaning just a touch west of OFCL.

Not much fall planting around here in IL. Very little wheat. Most fields still have standing corn and soybeans.
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Quoting redwagon:

When do you suppose Isaac might begin the turn NW or N?


Already is NW according to radar
Member Since: July 14, 2008 Posts: 1 Comments: 9648
ATCF says Kirk is up to 50mph (45kt) and down to 1005mb.

Prayers to all those out there in Isaac's path.
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if you live in PR or the Lesser Antilles i would keep a vary close eye on 98L has some of the mode runs are start too point tours you


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Quoting cwolfsheep:


Most of the system is on land now. A blogger did a nice writeup on the data viz for this.



What a stunning visual. I'll go read the write-up, because I'm willing to pay for this.
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Quoting sunlinepr:


The lesson that should have been learned from Katrina, for some, has been forgoten...

In NOLA, when there is a Hurricane, if your home is in inundable areas and there is a MANDATORY evacuation... you have to leave... How come we see people being rescued from the roofs... - "the ones that could breach throug it"... what about the old ones or dissabled who didn't had the strenght to open an escape in the roof?.... Right now, many houses are completly under water, you can't even see the roof... That irresponsibility puts in danger those who have to go and rescue those who didn't leave...


As has been asked by many today can't you guys wait to play the blame game after this disaster is over?
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448. CJ5
98l is going to have to find away to avoid the sweeping trough. All models show it being picked up and swept away. There are a few days to go so we shall see.
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Quoting DavidHOUTX:
Cool Radar Loop goes out to about 120 hours.


http://weatherspark.com/#!maps;a=USA/LA/New_Orlea ns


I forgot to add that this loads really fast too.
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Quoting VirginIslandsVisitor:
Is it just me or is the blog suffering from a major lag?


Very quiet considering.
Hope everyone is out of harm's way.
I assume that some of our bloggers don't have power.
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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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