Isaac slamming Gulf Coast with damaging floods, tornadoes

By: Dr. Jeff Masters , 4:44 PM GMT on August 30, 2012

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Slow-moving Tropical Storm Isaac continues to hammer coastal Louisiana, Mississippi, Alabama, and Florida's Panhandle with tornadoes, torrential rains, high winds, and a damaging storm surge. Over the past 24 hours, destructive tornadoes have touched down in Biloxi and Pascagoula, Mississippi, and one person was killed by a tree falling on a car in Pearl River County, Mississippi. A major flood event is occurring in Slidell, Louisiana, where Isaac's storm surge filled Bayou Bonfouca and the W-14 Canal, inundating portions of the city with 1 - 5 feet of water. While Isaac is now a weakening minimal-strength tropical storm, it is still a potent rainmaker, and will cause damaging floods all along its path for the next three days. Major river flooding is occurring or is about to occur on a number of rivers in the landfall area. In north central Tangipahoa Parish in southeast Louisiana and southwestern Pike County in southern Mississippi, a mandatory evacuation has been ordered for all low-lying areas and along the Tangipahoa River, due to the potential failure of the Lake Tangipahoa dam. Audubon Park in New Orleans, recorded 11.19" of rain as of 7 pm Wednesday night. An earlier amount of 19" was found to be erroneous, and this is not a 24-hour precipitation record for the city. According to wunderground's weather historian, Christopher C. Burt, New Orleans' greatest 24-hour rainfall on record is 14.01" on July 24 - 25, 1933. The Louisiana official state 24-hour record is 22.00" on Aug. 29, 1962 at Hakberry, although U.S. Army Corps of Engineers `Storm Studies' mentions a 23.80" falling in a 24-hour period at Millers Island during a TS on Aug 7-8, 1940. Storm total was 37.50" over a 60-hour period there during that event.

A few other rainfall totals from Isaac, through 11 am EDT on Thursday:

15.02" Marion, MS
10.09" Hattiesburg, MS
10.15" Gulfport, MS
9.80" Slidell, LA
9.74" Biloxi, MS
8.52" Mobile, AL
5.57" Baton Rouge, LA


Figure 1. Isaac's winds and storm surge overcomes the seawall and floods South Beach Boulevard in Waveland, Miss., Wednesday, Aug. 29, 2012, the seventh anniversary of Hurricane Katrina hitting the Gulf Coast. (AP Photo/Rogelio V. Solis). Waveland experienced a storm surge in excess of 5' for 36 hours.

Isaac's storm surge winds down
Storm surge levels along the coast of Mississippi and surrounding areas are gradually receding, and the surge has finally fallen below 5' at Waveland, which experienced a storm surge in excess of 5' for 36 hours. Isaac's storm surge levels were characteristic of a Category 2 hurricane, and lasted for an exceptionally long period of time. Waveland, Mississippi experienced a peak surge of 8' and peak storm tide of 9' (surge plus the natural high tide), which beat the levels that occurred during Category 2 Hurricane Gustav of 2008 (7' of storm tide.) The peak 11.06' storm surge at Shell Beach, which is in Lake Borgne, 30 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Gustav. According to an article in nola.com, Isaac pushed a storm surge of 13.6' into Lake Borgne, on the east side of New Orleans. This is not far from the 15.5' storm surge Hurricane Katrina brought to the location. It is quite possible that Isaac's storm surge might have breached levees of the east side of New Orleans, flooding areas inhabited by tens of thousands of people, had the Army Corps of Engineers not completed their $14.5 billion upgrade to the New Orleans flood defenses this year. I estimate that storm surge damage from Isaac will exceed $2 billion. Isaac has likely caused $2.5 billion in insured damage not related to flooding, insurance firm Eqecat estimated yesterday. Here were some of the peak storm surge values that were recorded at NOAA tide gauges during Isaac:

11.1' Shell Beach, LA
8.0' Waveland, MS
3.5' Pensacola, FL
4.6' Pascagoula, MS
3.8' Mobile, AL


Figure 2. A TRMM satellite 3-D view of rainfall on Aug. 28 showed a few very powerful thunderstorms near Isaac's eye were reaching heights of almost 17 km (10.6 miles.) Intense bands of rain around Isaac were occasionally dropping rain at a rate of over 2.75 inches per hour. Image credit: SSAI/NASA, Hal Pierce.

Isaac's storm surge on the Mississippi River
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. Since salt water is more dense than fresh water, the surge travelled along the bottom of the river, with the fresh water flow of the river lying on top. The surge continued upriver, and before reaching New Orleans, encountered an underwater barrier in Plaquemines Parish. This barrier was constructed by the Army Corps of Engineers beginning on August 15, in order to keep salt water from moving upstream and contaminating drinking water for Plaquemines Parish and New Orleans. Salt water had made it 90 miles upriver to the outskirts of New Orleans, due to the low flow rate of the river (which had dropped 7' below average in height due to the drought of 2012.) According to a spokesperson for the National Weather Service River Forecast Office, this barrier was probably able to completely block the flow of salt water upriver due to Isaac's storm surge, and no salt water made it as far as New Orleans. However, the massive intrusion of ocean water into the river channel caused the mighty Mississippi's fresh water flow to back up for hundreds of miles. Water levels were elevated by 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.

Hurricane Kirk in the Central Atlantic
Hurricane Kirk intensified into a 75 mph Category 1 hurricane this morning, becoming the busy 2012 Atlantic hurricane season's fifth hurricane. With the season's mid-point of September 10 still almost 2 weeks away, we've already had 12 named storms and 5 hurricanes, which is close to what an entire season experiences in an average year (11 named storms and 6 hurricanes.) Kirk should stay well out to sea and not trouble any land areas.


Figure 3. Morning satellite image of Hurricane Kirk.

Tropical Storm Leslie forms in the Central Atlantic
Tropical Storm Leslie has formed in the Central Atlantic. Leslie's formation on August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th storm. Only 1995 had an earlier formation date of the season's 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine)
formed on August 29th. Leslie is organizing quickly, and appears destined to become a hurricane before the week is out. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. In the long term, it remains unclear if Leslie will follow Kirk and fully recurve out to sea. The latest 2 runs of the GFS model have predicted that Leslie will recurve out to sea and not threaten any land areas, but the latest 2 runs of the ECMWF model have predicted that the trough of low pressure pulling Kirk to the northeast will not be strong enough to recurve Leslie out to sea. Instead, the ECMWF predicts that a ridge of high pressure will build in early next week, forcing Leslie more to the northwest, making the storm a potential threat to Bermuda, then to the Northeast U.S. and Canada in 8 - 11 days.

Jeff Masters

Hurricane Isaac Louisiana (apphotos)
Two men walk in the storm surge from Isaac, on Lakeshore Drive along Lake Pontchartrain, as the storm approaches landfall, in New Orleans, Tuesday, Aug. 28, 2012. (AP Photo/Gerald Herbert)
Hurricane Isaac Louisiana
west palm beach flood isaac (alishu)
West Palm Beach flood from Isaac
west palm beach flood isaac
Hurricane Isaac Impacts Navarre Beach & Pier10 (jennjeff1)
Hurricane Isaac versus Navarre Beach Pier, the longest concrete pier on the Gulf of Mexico
Hurricane Isaac Impacts Navarre Beach & Pier10

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Quoting PalmBeachWeather:
I did after I reread it.........Is reread a word?


Only if you read something more than once.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
Quoting JLPR2:
So where do you guys/gals think the center is? Under the deepest convection or in between the two strongest areas ?


You are assuming one center?
Member Since: August 4, 2007 Posts: 0 Comments: 2813
686. mks
Thanks Grothar. Next question now, If Leslie misses the first weakness how much of a chance does she have of impacting the northeast Caribbean?
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Quoting waterskiman:

LOL, I skip the spam, just get the reg ham in a can. In the old days they used to have bacon in a can, haven't seen that in a long time. You still have to cook it though
Beef Jerky is one of my priority meals... Was without power for weeks here after 2004 (Francis & Jeanne) and 2005 (Wilma)
Member Since: Posts: Comments:
Quoting Relix:
That subtropical ridge seems a tiny bit stronger in the new steering layers.



The new 18z models pick up on the weakness that Kirk is creating north of Leslie thus having to storm follow the weakness. I must add the weakness has shrunk as the subtropical ridge have strengthen some in the latest steering layers. Because it shrunk leaves a tighter window of recurvature so in order to have a complete recurve out to sea like the early 18z model suggest a sharper turn must occur. However the storm is racing west at 20mph (which seems to be the norm since Ernesto) which mean if it miss a tightening window of recurvature it might get trap under the strengthen ridge before a second trough tries to pick it up but we shall see how strong the second one will be.
Member Since: May 25, 2012 Posts: 0 Comments: 2043
Quoting JLPR2:
So where do you guys/gals think the center is? Under the deepest convection or in between the two strongest areas ?


Under the deepest convection.
Member Since: Posts: Comments:
Quoting washingtonian115:
D.
C.The state of Washington is really boring.Except for Seattle and if your in to Pine cone trees.

Washington is not boring.
-.-

It's one of the most beautiful states in the country IMO.
Member Since: Posts: Comments:
Quoting PalmBeachWeather:
If you have never tried the "Spam Lite" in the light blue can, it isn't too bad.... During a catastrophe one still has to watch one's weight

LOL, I skip the spam, just get the reg ham in a can. In the old days they used to have bacon in a can, haven't seen that in a long time. You still have to cook it though
Member Since: June 6, 2010 Posts: 0 Comments: 4371
Quoting TheHurricaneDundee:
oh. Hello lady ;)


LOL (JL)
Member Since: July 17, 2009 Posts: 64 Comments: 23749
679. JLPR2
So where do you guys/gals think the center is? Under the deepest convection or in between the two strongest areas ?

Member Since: September 4, 2007 Posts: 7 Comments: 8459
Quoting CosmicEvents:
Ocean interests=Fish storms in NHC parlance.
And rightfully so...there are ships at sea that are at risk. There's no risk for the fish.
Unless I can snag a Hogfish (Hog Snapper)
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Quoting WeatherNerdPR:

No. :(
dont worry, the carribean plate is moving ENE.
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Quoting mks:
Grothar, do you think that Leslie will get picked up by the through or might she miss the weakness and continue heading west?


There appear to be a number of weaknesses in the ridge. One could be caused by the wake of Kirk and another in a few days with a very strong trough expected. Now there could be different reasoning with the ECMWF moving a little more west than the other models right. One could be they expect Leslie to miss the first impulse, or just be pulled a little North and resume a west motion, then begin to get pulled North by the 2nd weakness a little later.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
Ocean interests=Fish storms in NHC parlance.
And rightfully so...there are ships at sea that are at risk. There's no risk for the fish.
Member Since: August 3, 2005 Posts: 10 Comments: 5462
Quoting waterskiman:

Totally agree. I have more stuff than you can poke a stick at. What ever is on sale can wise or rice, beans coffee I buy it a bit at a time. vaccum pack the beans and the rice throw them in my food locker on the boat, even if it sinks I can recover all of it.
If you have never tried the "Spam Lite" in the light blue can, it isn't too bad.... During a catastrophe one still has to watch one's weight
Member Since: Posts: Comments:
Quoting NEWilmNCTP:
Here on the East coast as well as the Gulf coast we are told to have at least 3 days worth of water and food supplies on hand. To complain after 8 hours sounds like someone just wants to make a political statement against a governor. Take responsibility for yourself and family.


You should read and understand the context of the post before responding. The EOC took 8 hours to arrive with the water after they initially called 2 DAYS AFTER IT STOPPED RAINING.

Granted it wasn't 3 days later and I'm not here to discuss their lack of planning. What I am here to discuss is the county's lack of following through with what they communicate to the public.

"We'll get you what you need quickly." - 8 hours later
"We're going door to door to make sure everyone is ok" - Haven't seen anyone for the past 3 days since it stopped raining.
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Quoting mitthbevnuruodo:


As some may know, I live in the UK, def not hurricane country...not even tornado or earthquake country. Ok, it is a bit of rain and wind country, and maybe cause I grew up in earthquake country, I am always prepared for 'something'. I live at the top of the hills, so not in a flood risk area (always avoid those if I can), 'can' get snow in the winter...but nothing like the northern US. I'm def not rich, I'm pretty poor at the moment from various circumstances...but I still manage to be prepared 'just in case'. So, I do have a hard time seeing people in a hazardous area not having enough supplies for 2 or 3 days. I have enough supplies for a few weeks, and I'm not anywhere hazardous compared to many places in the US. Maybe I'm just paranoid and they're optimistic!??!


Good strategy mate! Same here, I live in the UK, weatherwise in a 'boring' area, not flood prone nor will I get snowed in in winter. Nonetheless I always have non perishables for at least 4-5 days in my flat.
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Quoting Hurricanes305:


Find that unlikely the storm needs to slow down and intensify quickly to do a sharp turn. However there is excellent model consensus through 5 days.


It is possible that at the current speed she would near the weakness much faster. Many storms do quick turns at that speed; depending on the strength of the weakness and the steering currents.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
Quoting sar2401:


Yes, you are paranoid....but in a good way. :) In todays world of terrorist attacks, there may be no government that's able to help you. Assuming you're on your own for at least three days just makes sense. It doesn't even cost that much. Every time you shop, just pick up one extra item. In a couple of months, you'll have a basic stock of food and water that will get you through. I'm glad to hear that even people who don't face reoccuring hazards are prepared for one, just in case.

Totally agree. I have more stuff than you can poke a stick at. What ever is on sale can wise or rice, beans coffee I buy it a bit at a time. vaccum pack the beans and the rice throw them in my food locker on the boat, even if it sinks I can recover all of it.
Member Since: June 6, 2010 Posts: 0 Comments: 4371
Quoting JLPR2:


Why? I like my tropical climate.
Also, if we see snow the world should be ending. xD

You'll need some significant global cooling to get snow down there :)
Member Since: Posts: Comments:
667. JLPR2
Quoting stoormfury:
The track and speed of Leslie is begining to be one of ooncern for the lesser antilles. IF the storm is at 50w and still south of 15n by tomorrow
morning then this could spell trouble for th islands.


I'm thinking it could cross 20n around 60w, but that is just my opinion.
Member Since: September 4, 2007 Posts: 7 Comments: 8459
Quoting Grothar:
The early 18z models have Leslie turning sharply North.



Find that unlikely the storm needs to slow down and intensify quickly to do a sharp turn. However there is excellent model consensus through 5 days.
Member Since: May 25, 2012 Posts: 0 Comments: 2043
Quoting TheHurricaneDundee:
Wait a minute are you saying you think im a woman or are you?
LOL......No, I am the she
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664. mks
Grothar, do you think that Leslie will get picked up by the through or might she miss the weakness and continue heading west?
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Quoting CASANOVA7823:
How can I obtain a satellite image loop for Leslie on my mobile device? Thanks..
http://www.ssd.noaa.gov/PS/TROP/floaters/12L/imag ery/swir-animated.gif
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Quoting CybrTeddy:
Eye becoming increasingly better defined in Kirk.


Nice work Kirk!
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Other models also reflect a sharp Northern turn.




The trickiest part of a Hurricane is always the intensity. But most are in agreement of a very potent storm.


Member Since: July 17, 2009 Posts: 64 Comments: 23749
660. JLPR2
Quoting WeatherNerdPR:

I want snow in PR.


Why? I like my tropical climate.
Also, if we see snow the world should be ending. xD
Member Since: September 4, 2007 Posts: 7 Comments: 8459
658. Relix
That subtropical ridge seems a tiny bit stronger in the new steering layers.

Member Since: August 3, 2006 Posts: 0 Comments: 2639
Quoting Grothar:
As I did write earlier, this is going to be a very large storm and I think perhaps stronger than a Cat 3.

Looks like all this wish-casting Leslie West is starting to pan out.
Member Since: August 4, 2007 Posts: 0 Comments: 2813
I've also been rooting for El Nino... I want snow.
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Quoting interstatelover7165:
Do you live where I think you live? DC or State?
D.
C.The state of Washington is really boring.Except for Seattle and if your in to Pine cone trees.
Member Since: Posts: Comments:
Here on the East coast as well as the Gulf coast we are told to have at least 3 days worth of water and food supplies on hand. To complain after 8 hours sounds like someone just wants to make a political statement against a governor. Take responsibility for yourself and family.
Member Since: Posts: Comments:
Quoting sar2401:


Yes, you are paranoid....but in a good way. :) In todays world of terrorist attacks, there may be no government that's able to help you. Assuming you're on your own for at least three days just makes sense. It doesn't even cost that much. Every time you shop, just pick up one extra item. In a couple of months, you'll have a basic stock of food and water that will get you through. I'm glad to hear that even people who don't face reoccuring hazards are prepared for one, just in case.
Oh my
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HPC precip map

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The early 18z models have Leslie turning sharply North.

Member Since: July 17, 2009 Posts: 64 Comments: 23749
Quoting mitthbevnuruodo:


As some may know, I live in the UK, def not hurricane country...not even tornado or hurricane country. Ok, it is a bit of rain and wind country, and maybe cause I grew up in earthquake country, I am always prepared for 'something'. I live at the top of the hills, so not in a flood risk area (always avoid those if I can), 'can' get snow in the winter...but nothing like the northern US. I'm def not rich, I'm pretty poor at the moment from various circumstances...but I still manage to be prepared 'just in case'. So, I do have a hard time seeing people in a hazardous area not having enough supplies for 2 or 3 days. I have enough supplies for a few weeks, and I'm not anywhere hazardous compared to many places in the US. Maybe I'm just paranoid and they're optimistic!??!


Yes, you are paranoid....but in a good way. :) In todays world of terrorist attacks, there may be no government that's able to help you. Assuming you're on your own for at least three days just makes sense. It doesn't even cost that much. Every time you shop, just pick up one extra item. In a couple of months, you'll have a basic stock of food and water that will get you through. I'm glad to hear that even people who don't face reoccuring hazards are prepared for one, just in case.
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Quoting WeatherNerdPR:

No. :(

:C
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Quoting Skyepony:
"I was posting back them but I heard the term as a kid."

Skye,
Maybe you typed it and the wu bloggers picked it up from you then. Wish I knew who said it on TWC today. Maybe he grew up with the term as you did. My ignorance is showing, as I grew up with earthquakes, not hurricanes, and never heard it before wu where it is used extensively.
;)

580. FunhouseFX 11:03 PM GMT on August 30, 2012
Thanks. Haven't seen Reed Timmer's TV show, but I do follow on i-net where he's chasing - just in case it's near me. lol I respect his knowledge.
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Quoting PalmBeachWeather:
I did after I reread it.........Is reread a word?
Yes.
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Quoting mitthbevnuruodo:


Sorry, I think he mistook you as making a statement...not asking a question
BTW..He is she
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Quoting Articuno:

Have you even been in snow?

No. :(
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Quoting mitthbevnuruodo:


Sorry, I think he mistook you as making a statement...not asking a question
I did after I reread it.........Is reread a word?
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Quoting WeatherNerdPR:

I want snow in PR.
Quoting WeatherNerdPR:

I want snow in PR.

Have you even been in snow?
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Quoting washingtonian115:
I personally want El nino so i can have a cold and snowy winter.
Do you live where I think you live? DC or State?
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Quoting NortheastGuy:
Moving at 21 MPH - It doesn't seem Leslie will be turning Northwest anytime soon. It would really have to slam on the brakes and take a sharp turn


New steering layer maps suggest that the subtropical high is becoming better define. As the trough over the Central Atlantic is flattening some. Lets see if this trend continues thus the model could shift west in response. IMO I believe this will gain more latitude than Isaac and Ernesto. this wont make it far in the Caribbean and at best it may graze the the NE Caribbean. However its quite likely that it will miss the Caribbean by 18-21 degrees before the ridge catch up to it and traps the system and forces it back west. However time will tell for the Northern Lesser Antilles should watch in cast the situation changes.
Member Since: May 25, 2012 Posts: 0 Comments: 2043
Quoting mitthbevnuruodo:


As some may know, I live in the UK, def not hurricane country...not even tornado or hurricane country. Ok, it is a bit of rain and wind country, and maybe cause I grew up in earthquake country, I am always prepared for 'something'. I live at the top of the hills, so not in a flood risk area (always avoid those if I can), 'can' get snow in the winter...but nothing like the northern US. I'm def not rich, I'm pretty poor at the moment from various circumstances...but I still manage to be prepared 'just in case'. So, I do have a hard time seeing people in a hazardous area not having enough supplies for 2 or 3 days. I have enough supplies for a few weeks, and I'm not anywhere hazardous compared to many places in the US. Maybe I'm just paranoid and they're optimistic!??!
Very nice and emotional statement...Thank you
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Quoting TheHurricaneDundee:
oh nothing nevermind


Sorry, I think he mistook you as making a statement...not asking a question
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The track and speed of Leslie is begining to be one of ooncern for the lesser antilles. IF the storm is at 50w and still south of 15n by tomorrow
morning then this could spell trouble for th islands.
Member Since: Posts: Comments:

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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.