Kudos to Derek Ortt and Daniel Stern for recognizing Katrina

[wxmann_91]

...was a Cat 3 at landfall.

They were the only ones to see, with the SFMR and sonde data, that Katrina was in fact a Cat 3 at landfall in Louisiana, and not a Cat 4 as many others here thought. And he stuck to it.

So I guess that's the end of the debate - whether you like the call or not - Katrina was a 3 at landfall.

(Edited since

credit needs to go to graduate student daniel Stern, who processed the NOAA dropsonde data for the wind speeds a few months ago. he brought this to my attention that this was in fact a cat 3 at landfall based upon the dropsondes

)

[quandary]

The wind damage was caused by a Cat 3 then, but the NHC leaves open the possibility that Katrina touched land as a Cat 4 (something about it was a Cat 4 a few hours before landfall and these could've reached the coast in isolated pockets). What does it really mean for a Cat 3 or 4 to hit land? If a Cat 4 hitting land means that the highest 1 minute sustained wind at a single or multiple points will be above 115kts and most people will get 100kt winds if they get a direct impact, then how is Katrina different from this?

[Derek Ortt]

when a cat 4 or 5 hits land, it means that total destruction can be caused by wind alone,. Charley produced less surge than TS Gabrielle did, its winds were powerful enough to devastate everything

I want anyone who still lives in New orleans or is planning to go back to know this. The city did NOT experience a major hurricane. Please do not be lulled asleep into thinking katrina was as bad as it gets. if a 4 moves into the city, vertical evacuation is not possible as the winds will destroy anything above the surge

[DESTRUCTION5]

when a cat 4 or 5 hits land, it means that total destruction can be caused by wind alone,. Charley produced less surge than TS Gabrielle did, its winds were powerful enough to devastate everything

I want anyone who still lives in New orleans or is planning to go back to know this. The city did NOT experience a major hurricane. Please do not be lulled asleep into thinking katrina was as bad as it gets. if a 4 moves into the city, vertical evacuation is not possible as the winds will destroy anything above the surge

Basically with as bad as this season was...We did not see a Cat 4-5 in the US....Period..

[Derek Ortt]

Wilma may be upgraded to a 4 as the FL winds were right on the border of 3/4 at landfall. BT not conclusive yet since it hit between points

[Derek Ortt]

with regards to the first post

credit needs to go to graduate student daniel Stern, who processed the NOAA dropsonde data for the wind speeds a few months ago. he brought this to my attention that this was in fact a cat 3 at landfall based upon the dropsondes

[Tampa Bay Hurricane]

Kudos to Ortt and Stern

[wxmann_91]

with regards to the first post

credit needs to go to graduate student daniel Stern, who processed the NOAA dropsonde data for the wind speeds a few months ago. he brought this to my attention that this was in fact a cat 3 at landfall based upon the dropsondes

Title has been edited to give Mr. Stern credit as well.

[Jam151]

and this is important for the levee designs in New Orleans so it DOES matter. Kudos Ortt.

[Derek Ortt]

what this tells us is... actually design the levees to withstand a category 3 hurricane, and the region will be many times safer. We had levees that failed in cat 1 conditions

[f5]

isn't this the same reliable SFMR record 165 mph sustained winds at landfall?

[vbhoutex]

what this tells us is... actually design the levees to withstand a category 3 hurricane, and the region will be many times safer. We had levees that failed in cat 1 conditions

Did the levees fail in CAT1 wind conditions or CAT1 surge conditions? There is a difference. The last "official" report I heard(on the news) is that the levees did perform to the level they were expected to. That is why I am asking this question. There had been some speculation that they were not designed properly and this report debunked that. We all know that the surge conditions were well above what one would expect from a CAT1 hurricane everywhere in LA and MS from the landfall point East.

[Derek Ortt]

the industrial canal maybe

but not the 17th street canal. That surge came from the Lake, which received sustained cat 1 winds. The industrial canal, which wiped out the 9th ward, came up the intracoastal waterway, and was an upper 2/lower 3 type surge. however, the 17th street canal... it failed royally

[Margie]

When I get home (which unfortunately will be rather late tonight), I'll post some links, if they still exist. There was a spate of news articles about the design and construction of the canal walls. Apparently construction was not up to par. The company found problems and I believe it was because of the soil. As they were building the walls, they were coming out of alignment. They asked for more money to do the job correctly and usace said no; they then took them to court and usace won, said thank you very much, what you built will be just fine. It was not. Remember that Rita's rains produced an additional break in the Industrial Canal wall.

I took a mental health break from work

Found this article which seems to indicate that Industrial Canal may have been overtopped, thanks to MR GO. Also one of the few mentions of the horrific flooding that occured in St Bernard, inundating the entire parish (hard to understand why this, like the MS Gulf Coast, hardly received any press either), and also around central Plaquemines.

http://2theadvocate.com/stories/092205/ ... e001.shtml

And here is a more recent article on the 17th St Canal slamming usace.

http://www.nola.com/news/t-p/frontpage/ ... 287360.xml

I just want to print part of the article which explains very clearly how inadequate the design was.

Team Louisiana, which consists of six LSU professors and three independent engineers, reached its conclusions by plugging soil strength data available to the corps into the engineering equations used to determine whether a wall is strong enough to withstand the force of rising water caused by a hurricane.

"Using the data we have available from the corps, we did our own calculations on how much water that design could take in these soils before failure," said LSU professor Ivor van Heerden, a team member. "Our research shows it would fail at water levels between 11 and 12 feet -- which is just what happened" in Katrina.

Several high-level academic and professional investigations have found that the sheet piling used in the design to support the floodwalls was too short for the 18.5-foot depth of the canal. In addition to holding up the concrete "cap" on the walls, the sheet piling is supposed to serve as a barrier preventing the migration of water from the canal through the porous soils to the land side of the levee, an event that rapidly weakens the soils supporting a wall and can cause it to shift substantially.

The corps has long claimed the sheet piling was driven to 17.5 feet deep, but Team Louisiana recently used sophisticated ground sonar to prove it was only 10 feet deep.

Van Heerden said Team Louisiana's latest calculations prove investigators' claims that a depth of 17 feet would have made little difference. He said the team ran the calculations for sheet piles at 17 feet and 16 feet deep, and the wall still would have failed at a load of 11 to 12 feet of water.

Investigators have been puzzled by the corps' design since it was made public in news reports. They said it was obvious the weak soils in the former swampland upon which the canal and levee were built clearly called for sheet piles driven much deeper than the canal bottom. It was not a challenging engineering problem, investigators said.

Prochaska said a rule of thumb is that the length of sheet piling below a canal bottom should be two to three times longer than the length extending above the canal bottom.

"That's if you have uniform soils, and we certainly don't have that in the New Orleans area," he said. "It kind of boggles the mind that they missed this, because it's so basic, and there were so many qualified engineers working on this."

Here is the article about the contractor taking USACE to court:

http://www.msnbc.msn.com/id/9532037/

And here was one of the original articles where, after USACE went public with the claim (which they later quietly withdrew) that the failures were due to being overtopped by the surge, LSU expert Van Heerden talking about the certainty that the canal wall failures were due to design or construction errors, just from their surge model results, even before he went out and examined the canal walls directly.

http://www.washingtonpost.com/wp-dyn/co ... 01894.html

[MGC]

The surge that caused the failure of the Industrial Canal levees traved up the Mississippi River Gulf Outlet from Lake Borgne. The surge that caused the 17th Street Canal and London Ave Canal failures was from Lake Ponchartrain.

Having just finished reading the the tropical cyclone report on Katrina, all I can say is thank God that an EWRC was ongoing when Katrina made landfall. A little dry air helped too. Katrina was in the process of reforming a new eye as the hurricane reached the LA/MS coast. It is a pity the Slidell radar went down as much better wind estimates would have been available as the new eyewall crossed the coast in Pass Christian.....MGC

[Jam151]

No comments from those denying it was a three?

[MGC]

Margi, the article on the 17th street levee is wrong. The sheet pilings were the correct depth when a few were pulled out. What apparently happened was the weight of the water forced the earth behind the levee to migrate away from the canal allowing the surge to pour in. Once the water started flowing though a seam in the levee it erroded the earth which led to additional segment failure.

The levees in St. Benard and NO East were overtopped.......MGC

[Jim Cantore]

at the location of her first gulf landfall it may have been difficult to tell wind from surge damage

but 3, 4, or 5 its still the most catastrophic disaster in U.S history

[Derek Ortt]

while I would have perferred 105 and 100KT at the two landfalls to be in better agreement with the data, taking any speculation out of the matter, I can accept 110 and 105KT much more than I can accept Ivan as 105KT. 100 for Ivan is even stretching it based upon the data and Katrina showed that it was more intense than Ivan

[HurricaneJoe22]

Hurricane Katrina weaker than first thought when it slammed Gulf Coast

By John Pain
Associated Press Writer
Posted December 20 2005, 9:11 PM EST

MIAMI -- Katrina hit the Gulf Coast as a Category 3 hurricane, not a Category 4 as first thought, and New Orleans and Lake Pontchartrain likely were spared from the storm's strongest winds, the National Hurricane Center said Tuesday.

New Orleans' storm levees were generally believed to be able to protect the city from the flooding of a Category 3 storm. But portions of the levee system were either topped or failed in the storm, leaving up to 80 percent of the city under water.

Katrina made landfall Aug. 29 with top sustained wind of about 125 mph, not the 140 mph that was calculated at that time, the hurricane center said in its final report on the costliest U.S. hurricane of all time.

New Orleans was also on the west side of the storm, which normally has weaker winds. Although an accurate reading of the highest winds in the New Orleans area were made difficult by the failure of measuring stations, the NASA Michoud Assembly Facility in eastern New Orleans measured a sustained wind of only about 95 mph, the report said.

Jim Taylor, a spokesman for the Army Corps of Engineers, said the levee system that protects New Orleans was built before the creation of the Saffir-Simpson scale of classifying hurricanes, so different parts of the system protect against varying levels of wind speed, storm surge and barometric pressure.

Generally, officials said the levees would protect against a fast-moving Category 3. Katrina was generally a slow-moving storm, Taylor said.

An investigation into why the system failed is under way. Taylor said the change in category won't affect the fixes being made now or plans for future changes, which are still be debated.

But Louisiana Sen. Mary Landrieu, a Democrat, said: ``This news further highlights the need for a full federal commitment to build the highest level of protection through levees and coastal restoration for New Orleans, South Louisiana and the Gulf Coast.''

Category 3 ranges from 111 mph to 130 mph, so Katrina was on the higher edge of that ranking. Category 4 runs from 131 mph to 155 mph. Katrina was a top-scale Category 5 with 175-mph winds while in the Gulf of Mexico.

The revision of its strength came after forecasters studied data from devices that were dropped into Katrina from hurricane hunter aircraft, hurricane specialist Richard Knabb and forecasters Jamie Rhome and Daniel Brown said in the report.

The change also came from reviewing readings from a device called a stepped frequency microwave radiometer, which measures wind speed by examining how sea foam is blown. Radar images taken by hurricane hunter aircraft also were used.

Accurate measurements of the height of Katrina's storm surge were also difficult because of instrument failures, the report said. An unofficial observation of a 27-foot storm surge in Hancock, Miss., was included in the report.

Katrina also showed that wind speed and minimum central pressure are not related on a one-to-one basis. A hurricane's winds are blown because higher-pressure air rushes toward the lower-pressure eye to equalize the difference. Typically, the lower the pressure, the faster the air speeds in.

Because the pressure around each storm is different, lower pressure doesn't always correspond to a specific wind speed. With Katrina's pressure of 920 millibars at landfall, the storm would have been thought to be stronger. But Katrina's pressure field was spread over a much larger area than normal, so the pressure around it wasn't as high. Katrina killed more than 1,300 people in Louisiana, Mississippi, Florida, Georgia and Alabama. It was expected to cost insurers at least $34.4 billion in claims. ___

Associated Press writer Michelle Roberts in New Orleans contributed to this report.