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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This blog has gotten so slow I think because of the number of users/lurkers on line. I will bid everyone adieu and head for home and the TV. God help all of you in Isaac's way.
Member Since: March 28, 2008 Posts: 0 Comments: 1532
Weather Research and Forecasting Model (WRF)

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Quoting alaina1085:

Thats north of new orleans.
Belle river/Pierre part was on the west side of Isaac where more of the dry air was, I think their fine. I have friends that live there and so far they are all ok.
Thank you so much for the info.
Member Since: September 7, 2005 Posts: 0 Comments: 274
Isaac IMO will probably be retired this year only if the USA nominate him because I don`t trust Haiti with nominations.Haiti and Mexico are only the countries that I don`t trust when nominations occur Haiti with Gordon and Hanna and Mexico with Karl and Alex I am shock that this 4 names continues.
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BULLETIN
TROPICAL STORM ILEANA ADVISORY NUMBER 9
NWS NATIONAL HURRICANE CENTER MIAMI FL EP092012
200 PM PDT WED AUG 29 2012

...ILEANA JUST BELOW HURRICANE STRENGTH...


SUMMARY OF 200 PM PDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...18.5N 113.0W
ABOUT 365 MI...585 KM SW OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...991 MB...29.26 INCHES
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Quoting cajunkid:

Link please....water in our house
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BULLETIN
TROPICAL STORM KIRK ADVISORY NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112012
500 PM AST WED AUG 29 2012

...KIRK STRENGTHENS A LITTLE OVER THE OPEN WATERS OF THE ATLANTIC...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...25.3N 47.6W
ABOUT 1110 MI...1785 KM ENE OF THE NORTHERN LEEWARD ISLANDS
ABOUT 1490 MI...2400 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES
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Quoting TropicalAnalystwx13:

And it's FREE! How cool is that.
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Is it just me or is it that Isaac has had landfall that the blog is slow? I'd really like some thoughts on what others think the track might be for the next day or two. And I mean the ones who have looked into it with all the factors incorporated.
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Quoting alaina1085:

About 45 minutes ago...


Hey is that pic near Lakeland Ave?
Member Since: July 14, 2008 Posts: 1 Comments: 9630
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Quoting gbreezegirl:
how far is that from you? I am worried about Belle River and Pierre Part.

Thats north of new orleans.
Belle river/Pierre part was on the west side of Isaac where more of the dry air was, I think their fine. I have friends that live there and so far they are all ok.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting dexware:
Baton Rouge here... not much rain to this thing yet, hope it will hold out like this.

Power went out this morning due to on little ole tree that Entergy should have cut a LONG time ago that I've been asking them to cut from around their lines. Very poor design. So I sit and look at my neighbor across the street with his motion light kicking off an on. Their power comes from another side of the neighborhood.

i'm in Denham Springs and it has been raining for several hours now.
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Quoting carpentergrl:



That area is sparsely populated but full of high dollar homes.


Thanks. I know basically nothing about the area, so I have no idea what sorts of impacts would be expected. But I do live in a place where a levee break would be unthinkably bad, so my heart goes out to anybody in that situation.
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That big trough looks like it may be gone before it can completely pick it up which then means it can get caught under the High if I was the Lesser Antilles and Puerto Rico I would keep a close eye on 98L. Could be stronger than Isaac.
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Quoting HurricaneHunterJoe:


Pretty amazing huh?


ok... i've been trying to understand this all day. that really is an eye, right?
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Quoting KatyMan:


I will be on St John over the Labor Day weekend for my daughters wedding. Saw a post about a 5.4 earthquake and 98 is off the coast of Afreca. Any comments about my coming week that you could give.


That's a yes on the earthquake.

Your guess is as good as anyone's at this point. We're supposed to go to Water Island for a long weekend camping trip and we're on hold too. We're giving it until tomorrow night before we make the decision.

I'll keep my fingers crossed for you though!

Keep an eye on Link as it has updated info on all the islands and can be a very big help in seeing the big picture when there's a storm coming in.

Lindy
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Quoting yoboi:


what time did ya take that pic???

About 45 minutes ago...
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting LurkyMcLurkerson:
Madisonville levee break

Just the basic news right now, search and rescue under way. No photos or updates about how bad the flooding is yet.



That area is sparsely populated but full of high dollar homes.
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Quoting alaina1085:

Thats where Drew Bree's lives!
how far is that from you? I am worried about Belle River and Pierre Part.
Member Since: September 7, 2005 Posts: 0 Comments: 274
Man, also, our friends in Mississippi have been hammered with strong winds, spot tornadoes, and a pretty massive storm surge inundating beach road and the surrounding business and casinos.....plenty more water coming that way too
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Thanks for the replys !! We didn't get it real bad. We have 36 mph sustained with a max gust of 54 mph. Just a little over 1/2" of rain.
leicaman, Hwy 14 area floods pretty readily with surge. I don't think we have the surge here. Maybe he lost power. If I hear anything from that area, I'll let you know !! I hope he's ok !
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Quoting JLPR2:
Clearly 98L's center is to the SE of the convection, here you can see a wind barb that also indicates a 1005mb pressure, 98L is organizing decently and pretty quickly, opposed to what has been the rule for this year's storms.


Most have struggled with dry air this year. Mid-level relative humidity values are in the 70s for this storm. Definitely favorable.
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Baton Rouge here... not much rain to this thing yet, hope it will hold out like this.

Power went out this morning due to on little ole tree that Entergy should have cut a LONG time ago that I've been asking them to cut from around their lines. Very poor design. So I sit and look at my neighbor across the street with his motion light kicking off an on. Their power comes from another side of the neighborhood.
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620. JLPR2
Quoting Gearsts:
You think we should watch 98L or is it going out to sea? Pattern is not as west as it was with Isaac plus 98L is orginizing quickly.


The models could change, but considering the agreement of the models on the track, it will most likely stay out of the Caribbean.
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Also, I-10 near LaPlace, and I-55 near the LaPlace are under water....those highways are cutoff
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Madisonville levee break

Just the basic news right now, search and rescue under way. No photos or updates about how bad the flooding is yet.
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Quoting gustaveye:
confirmed levee break in Madisonville just now on FOX 8 new orleans

Thats where Drew Bree's lives!
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Quoting JLPR2:
Clearly 98L's center is to the SE of the convection, here you can see a wind barb that also indicates a 1005mb pressure, 98L is organizing decently and pretty quickly, opposed to what has been the rule for this year's storms.



After the string of close to land storms, that we haven't really been able to enjoy from a meteorological standpoint, and had to worry about in terms of land impact, there is nothing I would love more than a beautiful Cat 4 that recurves east of Bermuda.
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Quoting alaina1085:

I have heard of it but cant place it exactly. Its around here tho. They would have been better off staying here lol, Lutcher got it worse then us.
So I heard, and Gramercy. Also have folks on Belle River near Pierre Part haven't heard from since this a.m.
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Quoting gustaveye:
confirmed levee break in Madisonville just now on FOX 8 new orleans

Oh wow, thats the northshore! No good.
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Quoting Bluestorm5:
Even though it's only a Category 1, this was a Category 3 surge IMO. Look at this video from Reed Timmer... hate him or not, he had captured the true force of what big Cat. 1 hurricanes could do with Category 3 surge.

Link


That was it? A boat still floating at a dock, some kind of tank or tank car off in the distance, and some water in the bottom of a parking structure? They were hiding out in the same parking structure that was shown? I didn't know Reed Timmer before but, if this is an example of his work, I'm not impressed.
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deleted...
One of them thar political thangs that I tend to type out, and nearly always delete before posting.
This time I accidentally clicked Submit when I meant to Cancel.
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Quoting gbreezegirl:
don't know but street address is Cypress Bend NE in Gonzales - they went to Lutcher to ride it out with some others in the family.

I have heard of it but cant place it exactly. Its around here tho. They would have been better off staying here lol, Lutcher got it worse then us.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
This is terrible... A heartbreaking situation.
Quoting gustaveye:
confirmed levee break in Madisonville just now on FOX 8 new orleans
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Quoting GTcooliebai:
That is true, sometimes if a trough is too weak and the storm is too far south it won't be able to feel the influence from the trough and continue on a westward track, as the high builds in over head after the trough lifts up or passes.


Thank you and if you all keep saying these things it's possible that one day my old brain will be able to wrap itself around all of it, heck they say anything is possible, right? :)
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Quoting USCGLT:
Notice the 70 MPH speed limit sign!!!


Good to see that Isaac saw the sign and decided to slow down a bit.
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EVERYBODY SHUT UP ABOUT POLITCS NOW
Member Since: February 11, 2012 Posts: 0 Comments: 9731
Quoting JLPR2:
Clearly 98L's center is to the SE of the convection, here you can see a wind barb that also indicates a 1005mb pressure, 98L is organizing decently and pretty quickly, opposed to what has been the rule for the year's storms.

You think we should watch 98L or is it going out to sea? Pattern is not as west as it was with Isaac plus 98L is orginizing quickly.
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confirmed levee break in Madisonville just now on FOX 8 new orleans
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Isaac doing quite a number on the gulf coast
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Quoting FOREX:


Right. I learn a lot from your posts. Where do you live?
Largo, FL. in the Tampa Bay area.
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Quoting alaina1085:

Do you know what their neighborhood is called?

Yes Reed
don't know but street address is Cypress Bend NE in Gonzales - they went to Lutcher to ride it out with some others in the family.
Member Since: September 7, 2005 Posts: 0 Comments: 274
Quoting MrMixon:


I thought radar tended to underestimate precipitation... and isn't it still raining?


im seeing numerous reports of 7"+ so far as of midnight last night per news stations in new orleans
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Quoting groundedpilot:
Just got power back in New Iberia ! Anybody hear about a levee break around Madisonville ?


I have a good friend on Hwy 14 in New Iberia - cannot reach him. How bad is it? Thanks for the reply
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Quoting gbreezegirl:
that is where all my husbands family is - I have a niece lives on Cypress Bend Ave on a pond that looks just like that in Gonzales.

Do you know what their neighborhood is called?
Quoting RitaEvac:


Gonzales?


Yes Reed
Member Since: August 2, 2006 Posts: 0 Comments: 1240
597. JLPR2
Clearly 98L's center is to the SE of the convection, here you can see a wind barb that also indicates a 1005mb pressure, 98L is organizing decently and pretty quickly, opposed to what has been the rule for this year's storms.

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Quoting groundedpilot:
Just got power back in New Iberia ! Anybody hear about a levee break around Madisonville ?

Haven't heard anything about Madisonville, there was a significant breach in Braithwaite.
Member Since: July 24, 2008 Posts: 0 Comments: 156

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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.