Katrina H-Wind Analysis, marginal 3 at landfall

[Scorpion]

A 918 mb hurricane with 115 mph winds? I don't believe it.

[mtm4319]

I don't see how this is new evidence or anything that would lead to the data becoming "very conclusive" since this is these are the same claims posted at the beginning of the thread from the same sources.

I'll reiterate that if the winds were of category-3 strength, then the SS scale is much less useful than we previously thought and something needs to be done about it.

[timNms]

It appears to me that some on this board like to "Stir the pot" as it were. Read the whole article and you will find some interesting things in it.

From the article: "Powell noted the revised wind analysis was conducted under an experimental program and should not be considered official.He said the new readings could be off by as much as 10 percent, which still would make Katrina a Category 3 at landfall."

I think the key words here are EXPERIMENTAL

From the article: "The National Hurricane Center regularly re-examines storm parameters to determine the validity of initial information. For example, in 2002, 10 years after it made landfall in Miami-Dade County, Hurricane Andrew was upgraded from a Category 4 storm to a Category 5.

In its original reports on Katrina, the hurricane center reported the storm struck near the town of Buras, about 55 miles south of New Orleans, with 145 m.p.h. winds and weakened to 125 m.p.h. when it was about 35 miles east of the city, all the while pounding the levees."
http://news.yahoo.com/s/chitribts/20051 ... sdowngrade

I think I'll stick with the NHC on this one.

Question for those who probably haven't thought about it. According to the article, there were instruments placed along the LA and MS coasts that were supposed to measure the winds. Wouldn't those instruments have been covered by the surge? If that is the case, then how can they have an accurate measurment of the windspeed?

From the article: "The lowered measurements were gleaned from data sources that were unavailable while the hurricane raged, Powell said.

Those include ground-based instruments around southeast Louisiana and the Mississippi Gulf Coast set up by Texas Tech University and the University of Louisiana at Monroe."

[djtil]

yes...we know the "official" nhc intensity at landfall....this wasnt based on anything much really.....except continuity from recon missions about 24 hours before landfall.


no recon, sfmr, nothing really supported the 145mph official landfall intensity.

[LAwxrgal]

Wow, this thread is 14 pages....

I suppose the debate will continue at least until the NHC does its best track -- and maybe after

I haven't looked at much data because I wasn't here, but did this storm have much of a western side at landfall?

[wxman57]

Then I really think some previous storms need to be readjusted. Surge aside, I don't think we can put Hurricane Fran and Opal of 1995, and Hurricane Jeanne of 2004, as also having "marginal cat 3 winds" at landfall. Sheer wind damage from those storms was miniscule compared to Katrina's. I tend to agree with Derek...a sustained 120 mph wind can do tremendous damage...just think how much wind that actually is. I think it's more a matter of revising old storms downward.

Or perhaps if some were to argue that those storms had cat 3 winds, but in tiny spots, like Opal with the one streak near the east end of Choctohatchee Bay, Fran near Camp LaJeune, and Jeanne near Hutchinson Island, the aerial extent of cat 3 winds should be discussed. A storm with 115 mph over a 2 square miles should not be considered an equal hit to one with 115 mph over 80 sq. miles.

Very good points. In most hurricanes, the strongest winds are over only a tiny area. So most people who have "been through a hurricane" never really see actual sustained 75+ mph wind. But Katrina's strongest winds extended over a very large area. More people actually experienced Katrina's full fury than with some of the other hurricanes which have hit the Mississippi coast in the past.

Even 70 mph winds can completely destroy a home if the structure is breeched by flying debris. A window breaks, air rushes in, the roof lifts off, walls fly outward, and all that's left is the foundation. Doesn't take anywhere near a Cat 4 to do that kind of wind damage.

Well, I'll be driving down to Mississippi (Gautier) in a couple of weeks to try to rebuild my mother's home. We're bringing 50 sheets of sheetrock to replace all her walls from 4 ft down. Going to be a lot of work.

I look forward to some interesting hurricane conferences next spring. Hopefully, the AMS Conference on Hurricanes and Tropical Meteorology in Monterrey, CA April 24-28 has a special session on Katrina. You going to attend this year, Derek?

[Agua]

I'll say this, and it will not be popular, but the *wind* damage at my home in Ocean Springs, and I live 4/10 of a mile from the beach, was greater in Georges than from Katrina. Now, bear in mind that the precise center of Georges came right over my home, as compared to Katrina with the eastern most edge of the eyewall some 20 miles away. But a moderate to strong Cat 3 at landfall doesn't surprise me.

[djtil]

I'll say this, and it will not be popular, but the *wind* damage at my home in Ocean Springs, and I live 4/10 of a mile from the beach, was greater in Georges than from Katrina. Now, bear in mind that the precise center of Georges came right over my home, as compared to Katrina with the eastern most edge of the eyewall some 20 miles away. But a moderate to strong Cat 3 at landfall doesn't surprise me.

it pretty much comes down to people for some reason being unable to separate wind and surge and comprehending that the category ranking of hurricanes is only based on wind.

oh well...its not really impt either way.

[Brent]

I'll say this, and it will not be popular, but the *wind* damage at my home in Ocean Springs, and I live 4/10 of a mile from the beach, was greater in Georges than from Katrina. Now, bear in mind that the precise center of Georges came right over my home, as compared to Katrina with the eastern most edge of the eyewall some 20 miles away. But a moderate to strong Cat 3 at landfall doesn't surprise me.

Did the surge not reach your house???

[wxman57]

I agree. The angle of landfall is paramount. Look at Georges at Cat 2 with a 14 foot storm surge in 1998. But surge aside, when has a Cat 3 storm ever caused a 25-30 ft. storm surge, at any angle? A good example is Lili in 2002. Lili reached 145 mph/Cat 4 status in the central Gulf before weakening to a 105mph/Cat 2 at landfall in LA. There was no huge storm surge there. The surge in Katrina reflects it 923 mb pressure, not a dramatically weakened hurricane. Even Ivan was said to have 135 mph winds at landfall and Ivan's surge wasn't like Katrina's. The debate will continue but I would really like to know how a 125 mph storm could totally obliterate 80+ miles of coastline in Mississippi regardless of it's windfield size.

If you compare Lili's wind field side-by-side with Katrina's then you will see that Lily was TINY in comparison. Katrina had a huge are of hurricane force sustained wind compared to Lili. It's this large area of strong 50+ knot winds that built up the large storm surge (and 60-80ft waves). Lili just didn't have that kind of wind field, so the surge was much lower.

And you also have to consider that the coastal topography storm surge multiplier for where Katrina made landfall was 1.9 vs. 1.1 or 1.2 east or west of that location. Katrina hit in just about the worst place along the Gulf as far as storm surge potential goes.

As for Ivan, it had a huge wind field as well, as big as Katrina's. Ivan also produced huge waves offshore. But I think that actual wind measurements at landfall indicated that Ivan was weaker than Katrina at landfall, and Ivan was weakening very quickly at landfall. That, combined with a much lower surge mu;tiplier for Pensacola than western Mississippi probably accounted for the much lower surge there.

[Derek Ortt]

'I'll be at the conference again this year

[Anonymous]

As will I.

FYI...Katrina was a Cat 4...infact, from what I heard...winds are being increased at landfall from 120 kt to 125 kt.

[Agua]

I'll say this, and it will not be popular, but the *wind* damage at my home in Ocean Springs, and I live 4/10 of a mile from the beach, was greater in Georges than from Katrina. Now, bear in mind that the precise center of Georges came right over my home, as compared to Katrina with the eastern most edge of the eyewall some 20 miles away. But a moderate to strong Cat 3 at landfall doesn't surprise me.

Did the surge not reach your house???

Nope. I live in old downtown OS. The beach runs at a SSE - NNW angle, forming the eastern edge of the inlet to Biloxi Bay; it's not an east-west orientation. The water stopped about a block and a half from my house.

[Edited to include the following:] Glancing blow from surge against the western OS waterfront rather than head on.

[Derek Ortt]

I do not know what you have heard, but do not be surprised absed upon the data that even the Louisiana landfall is a cat 3. The doppler radar does not lie

Scorpion, you can believe what you want to, but that does not change the fact that it did occur, or the fact that the flight I was one into Rita showed a 911mb cat 3

[wxman57]

As will I.

FYI...Katrina was a Cat 4...infact, from what I heard...winds are being increased at landfall from 120 kt to 125 kt.

Floydbuster, were you at the AMS 26th conference on tropical meteorology in 2004 in Miami? I know I saw Derek there. Should be some interesting discussions next April in Monterrey, CA.

[Derek Ortt]

this is not the national hurricane conference. Typically, this conference is intended for the scientific community to discuss the latest research results, though anyone who pays the $350 can attend

[curtadams]

Some people are complaining about the SS scale. I'm not a big fan of the SS scale but, simply, the danger from a hurricane doesn't fit into a one-dimensional scale. Hurricanes kill and damage from at least *4* major mechanisms: surge, wind, flooding rain, and waves. Although they correlate, the correlation is very rough. It's pretty much possible to have major damage from any combination of the above while others are negligible, at least on a large scale. Safford-Simpson is used because the winds can be measured (although as this discussion reminds us hurricanes aren't homogenous over time or space) but none of the others can until it's too late. We forecast the others - but no forecast is perfect and all of them are tough to forecast.

To give an idea of how hard forecasting can be, Ivan made landfall about 80 miles from my parent's beachfront condo (in a complex) and utterly demolished the first floor and garage - 3 feet of sand in the lobby, doors ripped off, utilities and mechanicals ruined, milllions in damages. Dennis was about 30 miles closer and had the same windspeed at landfall - and didn't even wet the carpet. YET - Dennis flooded out a small fishing community nearly 200 miles further east of here! How do you predict that?

It would be nice if we could have a multigrade scale - surge/wind/flood - that people could use and respond to. But, at present, we can only give good estimates for wind - and even those have substantial error variance. It's not clear that a multidimensional scale would be properly interpreted by the public anyway. So, we use Safford-Simpson- it just behooves us to be aware of its limitations.

[JTD]

I just read that article from Yahoo.

It is an outrage that the NO levees failed for a category 1 hurricane

Who on earth designed these levees? They seem to have been incompetent at best.

Also,

I am wondering if the NGOM can sustain a category 4/5 hurricane at landfall (Opal, Lili, Dennis, Katrina, Rita all weakened) To me the westerlies and the CONUS atmospheric patterns prevent it.

Based on Katrina being a weak 3 but doing much more damage than Camille, I am very skeptical that Camille was a cat 5. I can't wait to see the re-analysis report on Camille or has it already been released? If so, please provide a link.

The implications of a borderline cat 2/3 as 115 is not that far away from 110 (cat 2) causing this much damage is staggering. I wonder how much of it is faulty bullding codes and I also wonder if a storm like this hitting Florida would have done the same level of damage to Fla as MS/Southern LA received.

[Derek Ortt]

the reanalysis of Camielle has not been done, but I am going to check to see what in the world the 190 m.p.h. winds were based on (my suspicion would be that was the 850mb flight level winds

[Derek Ortt]

I am going to start a new thread about Camielle, but the sustained winds at landfall WERE NOT 190 m.p.h. The report says those were the gusts