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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Zoom in and you can really get a good idea of the stadium effect of the eye. Not to mention you can see the overshooting cloud tops from the most recent convective bursts.

Kirk Visible Flash Loop
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I wish I could say Issac will be the last storm to hit land this year. Sadly to much time left.
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Quoting hydrus:
To boldly go where many canes have gone before...Cane Trek..


lol,


Too bad a tropical cyclone with the name Kirk hasn't made landfall on the west coast of the U.S. ;)
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Quoting clwstmchasr:


Don't know about a fish because it may threaten Bermuda. This is not the same as Isaac. At this point with Isaac is was a considerable threat to the Islands. All of the models want to curve Leslie north. Now having said that, I would not totally rule out it getting pushed back west when it gets north of the islands.


Cool. Thanks. Saw the Euro...that looks pretty interesting. Things have trended west this year..so we'll see.
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It almost looks like a stadium effect is developing. Kirks eye is so small that it appears less distinct then it really is. I would put it near 85 knots right now, but would not be surprised if it is anywhere from 75 to 100 atm.
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Here's our East Pac hurricane:

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Quoting HrDelta:


My thought would to be then to canal to the Mississippi though Lake Marephas to the Mississippi.

Eventually, we need to have a more permanent solution.


Freshwater, sediment diversion from Mississippi River could build wetlands in Barataria Basin

Link

It works, (great I might add) but oyster fisheries are fighting it every step.

I believe, and some data might point to this after this hurricane season, the levees along the Mississippi River (south of New Orleans) made the surge funnel up into Plaquemines Parish.

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After being briefly obscured, the eye of Kirk is becoming better defined. 75 knots is a good starting intensity for now.

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Quoting muddertracker:


jeez taz......whatever.




chill out due get some sleep it seems like you need some for working 12hrs days
Member Since: May 21, 2006 Posts: 5089 Comments: 114051
Quite depressing :

AFTER LESLIE THERE WILL BE PERIODS OF DRY WEATHER AND THE TRADE
WINDS WILL RESUME LATER IN THE WEEK. BUT OVERALL THERE WILL BE
ONLY LIMITED SHOWER ACTIVITY DURING THE AFTERNOONS IN THE WEST AND
THE EARLY MORNINGS ON THE NORTHEAST COASTS. NO SIGNIFICANT
TROPICAL ACTIVITY IS FORESEEN DURING THE NEXT 10 DAYS FOR THE
LOCAL AREA.


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Love that STOP sign photo in Dr Masters post. My new desktop background... For now.
Our front yard has looked like that twice: 1998 and 2005.
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Quoting Tazmanian:



well i cant help it if you are working 12 hrs days


jeez taz......whatever.
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Quoting muddertracker:


Just asking, Taz man...not making a declaration ;)Been working 12 hour days, cut me some slack.



well i cant help it if you are working 12 hrs days
Member Since: May 21, 2006 Posts: 5089 Comments: 114051
look back on the earlier blogs when Issac was coming off the Africa coast and the models were showing it curving well east of Bermuda and a LOT of people were believing the models then..things can and will change especially with our RELIABLE models..
Member Since: August 19, 2006 Posts: 13 Comments: 13451
it looks to me like Kirk had gotten a little bit of moisture shed off earlier from Leslie's moisture pocket.. that's going to end in a little bit, and my thoughts being that surge enhanced development of Kirk, the signs of weakening seem to line up with the timing of the surge ending. dry air is behind that and will soon be squashing convection from both the east and west.. opinions based from observing CIMSS precipitable loops.
Member Since: July 31, 2008 Posts: 0 Comments: 1320
Quoting Grothar:
Leslie has a very large cloud system around it. If it could consolidate, this could be a very large storm.



Hey Grothar, could Leslie be our 1-2 punch? Or you think it will be pulled up where kirk is and not amount to much?

sheri
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mississippi coast, ocean springs

raining hard, but first rain ive seen from isaac coming straight down for a change. end is near.
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Quoting MAweatherboy1:
Gro posted this already but the new Euro brings Leslie much closer to the US... Still offshore, but closer than the other models.



it also shows a TD off the SE coast same as the 00z Euro

Member Since: August 19, 2006 Posts: 13 Comments: 13451
Quoting muddertracker:


That's Norway...right?



Yes!!!!
Member Since: July 17, 2009 Posts: 63 Comments: 23710
Thanks for the blog on the storm, Dr. Masters. I live in Hattiesburg and I can believe that 10 inch measurement.

I believe the last time it wasn't raining was 9pm Tuesday night.
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Quoting Tazmanian:



guys stop calling Leslie a fish its way too early too tell on where its is going even it it dos go out too sea the more W or SW it gos the higher ch of hiting Bermuda so if it hits Bermuda its not a fish


Just asking, Taz man...not making a declaration ;)Been working 12 hour days, cut me some slack.
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Member Since: July 17, 2009 Posts: 63 Comments: 23710
In central Ms here. Getting a bit of a break from the rain, however, winds are still quite strong. Looks like my area will be getting those severe bands coming from Pascagoula later this evening. Seems like this will never end. Keeping fingers crossed that our power stays on. My daughter is almost due with twins, and can not take the heat. Everyone stay safe out there.
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Quoting yonzabam:



Right. Going to Spitzbergen.


That's Norway...right?
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Quoting muddertracker:
Leslie is supposed to be a fish...right?



guys stop calling Leslie a fish its way too early too tell on where its is going even it it dos go out too sea the more W or SW it gos the higher ch of hiting Bermuda so if it hits Bermuda its not a fish
Member Since: May 21, 2006 Posts: 5089 Comments: 114051
Quoting muddertracker:
Leslie is supposed to be a fish...right?



Right. Going to Spitzbergen.
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Portlight getting ready to remove a tree from a house. Live Feed
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To bad we can't get a good microwave pass, it would help us understand the inner core a little better.

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Quoting Grothar:
Leslie has a very large cloud system around it. If it could consolidate, this could be a very large storm.



Yes, and seems to be getting her act together quicker than most systems have this year.
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Issac is still a very big boy. I am in Houston and just looked at our area weather and it looks as though the bands of weather are reaching into the Beaumont area now. If we get anything here, I sure hope it is later tonight, my son has his first HS football game this evening.
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It seems the storms that have formed this year around Leslie's latitude or south have had a hard time separating from the monsoonal troughs that have accompanied them. Leslie seems to be right on the border line . I guess will know more in the next 12 to 24 hrs.
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Leslie is supposed to be a fish...right?
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This sounds like a broken record, but here's a picture of yet another tornado in Mississippi (Pascagoula). Isaac has been quite the multifaceted storm.

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Quoting tropicfreak:


Ummmm, pressure is still lowering.

So? Nothing supports more than 75kts.

Lots of dry air near Kirk... The NHC has noted that it will be vulnerable to occasional intrusions of it, slowing down strengthening.

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Quoting MAweatherboy1:
Kirk may have peaked, the eye is not as clear as earlier and convection has weakened... No evidence to support anything over 75kts.



UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 30 AUG 2012 Time : 181500 UTC
Lat : 27:37:19 N Lon : 49:49:12 W


CI# /Pressure/ Vmax
4.5 / 981.6mb/ 77.0kt


Final T# Adj T# Raw T#
4.5 4.5 4.1
Frame-by-frame will get you nowhere.
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Last nights run of the Euro shows a very interesting scenario:

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Quoting MAweatherboy1:
Gro posted this already but the new Euro brings Leslie much closer to the US... Still offshore, but closer than the other models.



Wait until you see the new models. :)
Member Since: July 17, 2009 Posts: 63 Comments: 23710
Link


guys here is a link to 12z euro
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Quoting wxchaser97:

I agree with that, I had him becoming a cat2 but that was in 1-2 days.


Storms of this size can really react quickly to the changing environment.

And it is doing just that.
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Quoting tropicfreak:


And at the speed she is moving at, that might keep her in check for a little while, and she may miss that weakness, and be forced further west. I don't like the looks of this at all.

Btw, this is NOT a 75 mph storm. A cat 2 at least.



I agree with that, I had him becoming a cat2 but that was in 1-2 days.
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Quoting MAweatherboy1:
Kirk may have peaked, the eye is not as clear as earlier and convection has weakened... No evidence to support anything over 75kts.



UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 30 AUG 2012 Time : 181500 UTC
Lat : 27:37:19 N Lon : 49:49:12 W


CI# /Pressure/ Vmax
4.5 / 981.6mb/ 77.0kt


Final T# Adj T# Raw T#
4.5 4.5 4.1


Ummmm, pressure is still lowering.
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Leslie has a very large cloud system around it. If it could consolidate, this could be a very large storm.

Member Since: July 17, 2009 Posts: 63 Comments: 23710
Kirk is a rather symmetrical hurricane.

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Kirk may have peaked, the eye is not as clear as earlier and convection has weakened... No evidence to support anything over 75kts.



UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 30 AUG 2012 Time : 181500 UTC
Lat : 27:37:19 N Lon : 49:49:12 W


CI# /Pressure/ Vmax
4.5 / 981.6mb/ 77.0kt


Final T# Adj T# Raw T#
4.5 4.5 4.1
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Quoting MonsterTrough:

you're confusing me. Are you talking about Kirk(the picture you posted) or Leslie (referring to she)?


The 1st paragraph was on Leslie.

2nd was on Kirk.
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Quoting Doppler22:

I agree... Kirk= much stronger then cat 1

I'm thinking 90-100 mph Hurricane Kirk as of now, but we shall see tonight, next advisory should go up as long as he maintains his current structure.
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Quoting tropicfreak:


And at the speed she is moving at, that might keep her in check for a little while, and she may miss that weakness, and be forced further west. I don't like the looks of this at all.

Btw, this is NOT a 75 mph storm. A cat 2 at least.



you're confusing me. Are you talking about Kirk(the picture you posted) or Leslie (referring to she)?
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Quoting tropicfreak:


And at the speed she is moving at, that might keep her in check for a little while, and she may miss that weakness, and be forced further west. I don't like the looks of this at all.

Btw, this is NOT a 75 mph storm. A cat 2 at least.



I agree... Kirk= much stronger then cat 1
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Isaac still looks pretty good.

Member Since: July 17, 2009 Posts: 63 Comments: 23710

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About JeffMasters

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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