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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Quoting hurricanehanna:
\
serious? Oy. We need to get Isaac outta here. Supposed to be between us and Baton Rouge around 7. Been having sustained winds around 35 with gusts up to 50 mph. Raining, but not bad. Really feeling bad for those to our East into Mississippi.


Yep! Unfortunately I don't think it is moving at all in my opinion. I'm just basing that on radar though. It is NW of where it was yesterday but not by much..
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Quoting Hurricanes305:


This could be Gustav back in 2008 note the error in the title ''Hurricane Tropical Storm Isaac.'' Anyways Insane video.

Well, it was a Hurricane and a TS.. but yeah.
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744. debrr
Levee problems anywhere near Lake Okeechobee are of great concern, I would think. The Palm Beach County levee mentioned in a recent post is only a couple dozen miles from that massive TOXIC lake.

I don't know the condition of the levees before the rains, but a 1928 hurricane-induced breach of the levees killed 2,500 people and flooded hundreds of square miles.
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Quoting redwagon:

Talk about great good luck if this precip model verifies. Everyone knows the midwest desperately needs rain, which Isaac is sending even now but



That little area of rain falling in smack dab middle of Centex is also where the harshest drought is unrelenting, especially considering that little area provides water to millions.



If we in Centex can borrow Isaac for just a couple of days, we promise we will return him to the cornbelt to resume his rainmaking.

Take him away, please
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742. Skyepony (Mod)
Just east of Bay St Louis, just a few ft off record. Looks like it is going down now that the tide is going out.

Member Since: August 10, 2005 Posts: 226 Comments: 39441
Quoting Articuno:
Dang, is this video REAL? :O


Someone said in the comments it's from 2008's Hurricane Dolly.
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Quoting Articuno:
Dang, is this video REAL? :O



This could be Gustav back in 2008 note the error in the title ''Hurricane Tropical Storm Isaac.'' Anyways Insane video.
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Quoting Michfan:


You can blame all the dams up river for that.


It's Bush's fault (kidding, just carrying on the political trend, forgive me).

yeah, everything I've read points to the lack of beneficial sediment from flooding (i.e. flood-control dams like you said) and continental shifting.
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Quoting Articuno:

Really?
Yes.That is dolly.The video was shot in South Padre Island.
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Quoting TomballTXPride:
Where's Chasey been today? I know she's in Slidell.


Slidell is having some flood issues, though I don't think I've heard anything awful yet. Just might be enough to be keeping her quite busy.
Member Since: August 26, 2012 Posts: 0 Comments: 368
Rapid Scan of Issac
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Quoting Hurricanes305:


Not a really good map but could be verified once this is all said and done!

It's a shocking map, Centex atmo has been running precip away for so long (18 months) it's astonishing to see any map with any accumulation for us.
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Quoting washingtonian115:
No.That is during hurricane Dolly four years ago.


Is anyone else waiting for Isaac to die?.

Really?
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Quoting dhcoop59:


Thank you. It's my friend's MIL who is 76 and she can't reach her by either landline or cell.

doesn't seem like an overreaction to worry, esp given her age. its already flooding, and it will be worse than it is now.
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Quoting alaina1085:
Link

Link to a video from the North Shore


Carolinas and the gulf coast in general have been the targets for tropical system lately. I haven't had a hurricane in Florida since 2005 (pending on if Beryl is going to be upgraded this offseason) and especially South Florida.
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Quoting groundedpilot:
I agree that the dams may be a partial part of the problem but no the sole problem ! If you fly over the coast or use Google Earth, you will see decades worth of canals and channels that were dredged to facilitate oil and gas production. I am definitely not blaiming the oil companies, but it would be nice if they would return the environment to what it was before they arrived ! JMO


Problem is that the natural sedimentary cycle that made most of that land was ruined due to water being diverted to other areas upstream for irrigation, flood control, etc... No one ever thought to think of what this would do in the long run.
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730. Skyepony (Mod)
North side of Lake Pontchartrain, just south of Coventry, LA.
Member Since: August 10, 2005 Posts: 226 Comments: 39441
Quoting Articuno:
Dang, is this video REAL? :O

No.That is during hurricane Dolly four years ago.


Is anyone else waiting for Isaac to die?.
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Dang, is this video REAL? :O

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Quoting alaina1085:
Link

Link to a video from the North Shore


Wow, I really hope everyone is okay.
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Quoting 4waters:


just the most recent from TWC - initial flooding bc of the lake inflow. expect winds to begin pushing the water from the lake, north in a few hours. the combination does not look good. leaving probably a good idea if you can.


Thank you. It's my friend's MIL who is 76 and she can't reach her by either landline or cell.
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I agree that the dams may be a partial part of the problem but no the sole problem ! If you fly over the coast or use Google Earth, you will see decades worth of canals and channels that were dredged to facilitate oil and gas production. I am definitely not blaiming the oil companies, but it would be nice if they would return the environment to what it was before they arrived ! JMO
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Latest from Louisiana

Army Corps of Engineers said it wouldn't be able to lend an opinion until Thursday morning on whether blowing a hole in the east bank levee of Plaquemines Parish would help drain the flooded east side of the parish.
More than 600,000 homes and businesses were without power.
Twenty-two hospitals across the state are operating on generator power.
Storm surge of 11 feet reported in Shell Beach, La.
All flights are canceled at New Orleans International Airport.
Mississippi River at Baton Rouge was up 8.5 feet in 24 hours.
Officials have shut off water to LaPlace after concerns that water from Lake Pontchartrain could contaminate the water system.
Many parishes have extended their curfews and school closures.
Authorities in Plaquemines Parish have ordered a mandatory evacuation for a portion of the west bank of the Mississippi River. The evacuation affects people living from Venice north to the Oakville floodgate on Louisiana Highway 23. A shelter was to open at noon in Belle Chasse.
Member Since: September 5, 2007 Posts: 0 Comments: 3488
is it just me or did the center completly stop/ drift a bit south, it could be the convection easing into the eye though
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Link

Link to a video from the North Shore
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Quoting redwagon:

Talk about great good luck if this precip model verifies. Everyone knows the midwest desperately needs rain, which Isaac is sending even now but



That little area of rain falling in smack dab middle of Centex is also where the harshest drought is unrelenting, especially considering that little area provides water to millions.



If we in Centex can borrow Isaac for just a couple of days, we promise we will return him to the cornbelt to resume his rainmaking.


Not a really good map but could be verified once this is all said and done!
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Quoting TropicalAnalystwx13:
Hearing reports that a second levee has broke...this time on the north side of Lake Pontchartrain.
North shore on the lake(slidell and environs) also need to be on high alert. Thanks TA.
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It is really crazy how good he looks still. And he's moving _just a little faster_ than an average horse at a nice, steady walk, if anybody wants to use _that_ picture.

I really hope something in that ridge changes soon, or that someplace in his eye suddenly grows a mountain range. There is only so long structures can generally take this kind of thing, including levees. Any small, undetectable weaknesses that were there are getting hammered for days.

This sucks, y'all.
Member Since: August 26, 2012 Posts: 0 Comments: 368
From what I'm seeing and hearing from others who know the weather better than I....I'd advise all between NO and Baton Rouge to be on guard. Could be an extended heavy rain event next 24 hours in an area known for downed trees.
Stay safe.
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Quoting redwagon:

I sense an alarming Cerebellum.
Cerebrum would be more accurate.
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Quoting Hurricanes305:


Hope everything is fine with your family. hope this help:

Talk about great good luck if this precip model verifies. Everyone knows the midwest desperately needs rain, which Isaac is sending even now but



That little area of rain falling in smack dab middle of Centex is also where the harshest drought is unrelenting, especially considering that little area provides water to millions.



If we in Centex can borrow Isaac for just a couple of days, we promise we will return him to the cornbelt to resume his rainmaking.
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Quoting tatoprweather:
See the string of clouds in front of 98L....that's where 98L is going.


Can't base where a a system goes by cloud formation. You gotta look at the patterns and models that change constantly.
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Hearing reports that a second levee has broke...this time on the north side of Lake Pontchartrain.
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Here in Lake Chuck, LA, winds are 24mph with up to 37mph gusts and no rain yet. I hope this slow moving puppy peters out soon. Y'all stay safe on the other side of the state.
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Quoting oracle28:
scary photo


good example of why Isaac has done so well. He made more of a "swampfall" than a landfall. And the coastline just keeps eroding....
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Quoting dhcoop59:
It's hard to wade through the political crap to get info on affected areas. I have a friend that's desperately trying to get some info out of Slidell. Does anyone have a report from that area about conditions?

a lot of flooding there. i'm an hour west. a lot of roads flooded over. not hearing anything about wind damage.
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Quoting oracle28:
scary photo



You can blame all the dams up river for that.
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Quoting JLPR2:


Well according to that pass, the center is at 12.5n.


Quite low in latitude this trough may allow it to gain some latitude by tugging on it poleward. How if its not a deep system it might not be able to pick it up complete leaving it behind with the subtropical ballooning over it. However still too early the new 18z GFS run should come out any minute now.
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707. JLPR2
Hmm...

At least the eye is almost gone.
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...TROPICAL UPDATE:...

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scary photo

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Hello everyone, I live in a town right outside of Mobile,Al called Satsuma it has rained and rained all day. Sometimes just a little and sometime pretty durn hard like right know, wind is blowing and can't even see across Hwy 43. All our creeks and bayou are out in the woods or in folks houses. I wanted to say folks be very careful with this because of gators and snakes. All the creepy crawlys. I hope Pat and everyone in Louisiana are ok. I have prayed for you all all day. God Bless you all.

Sheri
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As Hurricane Isaac continues to push storm surge onto the north shore of Lake Pontchartrain, a number of houses are flooding in Slidell's Palm Lake subdivision, a Slidell Police Department spokesman said Wednesday afternoon.

Link
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Quoting DavidHOUTX:
Weather Channel just mentioned strong High Pressure to north of Isaac (100 degree Temp) -blocking N. Movement
Watch for S.W. Jogs
\
serious? Oy. We need to get Isaac outta here. Supposed to be between us and Baton Rouge around 7. Been having sustained winds around 35 with gusts up to 50 mph. Raining, but not bad. Really feeling bad for those to our East into Mississippi.
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Thanks for that!

I was hoping to find more of a street or neighborhood-level map, as the flooding in Laplace is varying by neighborhood. One of my cousin's houses is a loss, and the other is worrying about her home. Both houses are in LaPlace.

Quoting Hurricanes305:


Hope everything is fine with your family. hope this help:
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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
See the string of clouds in front of 98L....that's where 98L is going.
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698. JLPR2
Quoting Tropicsweatherpr:


Really PR? Where do you see it?


Well according to that pass, the center is at 12.5n.
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I see Isaac surpassed Ernie in ACE. Well done Isaac.
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Quoting JLPR2:


Actually a bit to the south of where the NHC has it, which is 13.3N.


Really JLPR2? Where do you see it?
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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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