Katrina H-Wind Analysis, marginal 3 at landfall

[sponger]

Wow, quite a popular subject. I didnt read through everything, but it looked like this storm was getting better organized right at 2nd land fall. Might account for higher gusts over coastal MS than typical Cat 3 would.

[f5]

the media like to say that its weakening even though Max Mayfield is on that network he does correct that "its weakening"rethoric very quickly

[DoctorHurricane2003]

The tsunami analogy was poor, especially considering that they move anywhere between 200-700 mph, with the global tsunamis in the upper range. Hurricanes don't move that fast.

But yes I do agree with the point stated that it does take longer for the surge to die down vs. the wind. We experienced it in Ivan last year, and Katrina this year. Considering that water is a denser substance than air, once it gets momentum, its going to keep going longer vs. air.

Its almost similar with temperature relations of air vs. water. We all know it takes much longer for water to heat/cool vs. air.........and that same general idea can be used with the movement of both.


Not that I agree that Katrina was a 100 KT storm, that's just bs. I believe it will be the job of this next generation of meteorologists to refine these new tools such as SFMR to show the winds more accurately, and to determine surface winds vs. flight level winds more accurately.

[Derek Ortt]

those H-Wind maps are not only based upon SFMR

Dropsondes from the NOAA aircraft and possibly doppler radar may be showing the same thing, while the AF data is indicating a cat 4. Maybe compromise and go with 110KT at landfall may be the way to go

[MGC]

If Katrina was a 100KT minimal Cat-3 at landfall in Mississippi then 95% of the hurricanes that have hit the US in the past century should be downgraded a couple of Cats. When was the last 927mb 100KT cat-3? Even is you ignore the water damage, the wind damage is some of the most extensive I have witnessed including Camille. Many well constructed homes in Diamondhead had their roofs ripped off.......MGC

[fasterdisaster]

those H-Wind maps are not only based upon SFMR

Dropsondes from the NOAA aircraft and possibly doppler radar may be showing the same thing, while the AF data is indicating a cat 4. Maybe compromise and go with 110KT at landfall may be the way to go

I agree, which is what it is set at.

[Derek Ortt]

one thing about that map that most are missing, the spatial extent of the 90KT winds are enormous, by far the largest I have ever seen. The 90KT winds covered the entire MS coast, which is why it didnt really make much of a difference where at in MS one was located, all areas had 90KT or higher sustained winds, with far higher gusts, for several hours

[Matt-hurricanewatcher]

There was data supporting Rita near 100 knots at landfall. So if Katrina was only 5 to 10 knot stronger...Then why was Katrina a hundred billion with Rita only being a 5 billion dollar storm. They where both cat5s...Which had a very big surge....

[Derek Ortt]

very easy

Rita hit a very unpopulated stretch of coastline. Except for Cameron, there was nothing to damage(or not very much). Compared to Gulfport and Biloxi

[curtadams]

There was data supporting Rita near 100 knots at landfall. So if Katrina was only 5 to 10 knot stronger...Then why was Katrina a hundred billion with Rita only being a 5 billion dollar storm. They where both cat5s...Which had a very big surge....

1) Katrina had a much higher surge. Maybe 35 feet rather than 20 feet. Perhaps because she was larger, perhaps because she approached the shore directly, and perhaps because the shape of the Mississippi Sound trapped the water. Call the surge people in a year or so when they figure it out.

2) Katrina hit a much more developed area. The Mississippi coast had something like 350,000 inhabitants mostly right on the coast, and New Orleans is over 1 million in the metropolitan area. There's little right on the TX-LA border coast - Cameron Parish, ground zero, has but 10,000 and they mostly live somewhat inland. Plus there is *no* major city there.

So more water and more to damage.

[MGC]

Is it possible that Katrina winds were stronger near the surface than at flight level? This has been observed in other strong hurricanes. Still can't believe that Katrina was only 10mph stronger than Georges despite a central pressure difference of about 35mb......MGC

[Anonymous]

Is it possible that Katrina winds were stronger near the surface than at flight level? This has been observed in other strong hurricanes. Still can't believe that Katrina was only 10mph stronger than Georges despite a central pressure difference of about 35mb......MGC

It was not...same thing happened with Ivan. This "data" was brought up, showing Ivan as a Cat 2...and it was an obvious Cat 3. Waveland, Pass Christian, Bay Saint Louis and Plaquemines Parish probably, for a very short amount of time, recieved 140 mph sustained winds. This would be supported by Mark Suddeth's gust to 137 mph on the Mississippi coast.

[Derek Ortt]

before I flew into Rita, I would have not believed it was possible for a 927mb hurricane to have winds of 100KT, or even 918. But we had a 911mb cane with 110KT surface winds. What may have happened, I'd have to look at the vertical velocities to be sure, is that the convective activity had decreased and it was stratiform, as flight level winds near MS were 127KT and 134KT near Louisiana. The 90 percent rule may not have held (this applies only to 1 minute sustained winds, gusts of course may have been 20-25KT higher than the sustained wind, and could have been frequent). More investigation is needed regarding this very interesting internal dynamic of major hurricanes

[Derek Ortt]

Naso,

Just how in the world does a gust to 137 m.p.h. justify sustained winds of 140 m.p.h.?

I can say with 100% certainity, 140 m.p.h. is not going to be the MS landfall intensity

[Radar]

Whether or not Katrina's winds were Cat 3's or Cat 4's is irrelevent here. Obviously we have seen Cat 4 damage well inland and Cat 5 near the beach which can be contributed to several different factors....

1. A Cat 5 storm surge (the worst in the history of the U.S.)
2. Many many tornados (I havent heard an official count but I know from what I have seen there had been alot and several people I had talked too witnessed them)
3. Being hammered relentlessly for hours by her winds (sustaining Cat 3 winds over an extended period of time with higher gusts can certainly cause Cat 4 type of damage).

So it seems to me to argue is futile and for those of you who say there is not Cat 4 damage I would love to invite you down for a weekend and take a grand tour...

[jasons2k]

(pulls up a chair)
I have to say this is one of the best threads we have going. A great debate without it spiraling out of control (so far).

[StormSkeptic]

I must agree this a very interesting intellectual discussion. Been following it all day. Let me see if I can add my take on it - and keep it going for another 6 pages:

1. Saying somthing is Cat 4 damage seems a bit of a misnomer. While the Saffir-Simpson scale relates the Cat to typical damage, the scale is based on the 2 minute top sustained wind speed. Not sure how the damage level was determined, but likely subjective and based on a more typical hurricane, where the top winds are confined to a small area. As was noted earlier in the thread, the wind damage is related to both the speed and duration (not to mention how well the structures are made.) So a 100mph sustained wind for an hour might very well cause the same damage as as sustained 135 mph wind for 2 minutes. This same debate happens over the Fujita scale, which comes at it from the other angle and is based on damage assessments - which are very subjective and also subject to the top speed vs. duration problem.

2. Sustained winds over land at the surface seem to rarely live up to the Cat rating unless the storm has very strong convection ongoing that can bring the winds right down to the surface. This kind of convection is usually only present in strong eyewalls, which are associated with strengthening systems at landfall (e.g., Charley, Andrew.) This was clear in the Charely videos I saw where the stongest winds only occured during the heaviest precipitation. Otherwise, the winds tend to be much lower and only gust to the Cat level. This is especially true in weakening systems, like Katrina, where the wind reduction to the surface may be 30% (the more stratiform stomrs like Derrick points out.) Weakening systems tend to produce winds of about a Cat lower then the flight level would suggest.

3. Storm surge is also a product of many things - not just top sustained winds over a small area. Surge depends on the wind speed, fetch ( distance of the wind over the water), the topology of the near shore waters and teh angel of approach. Like wind damage, surge can not always be directly related to just the Cat - which is based only on the max sustained wind (which may exist over a small area.) Once again, Katrina's winds were very strong over a large area for a long time - which led to a cat 5 surge - even with maybe cat 3 winds at landfall.



Bottom line is:
- As Derrick pointed out - the objective analysis would indicate that the top winds were low end Cat 3 - by the Saffir-Simpson scale definition -but the extent and duration could very well have produced Cat 4 or 5 damage over a wide area. The Saffir-Simpson scale is narrowly defined by one dimension, but wind damage and surge depends on more dimensions - so the cat rating may not be in sync with the resultant damage. The two-minute max sustained wind just doesn't fully capture the destructive potential of a storm. A new, or supplemental, rating system should really be developed to acount for these other dimensions.
- Katrina's top winds were lower than the barometer reading would suggest because it was weakening and the windfield was spreadout. The energy represented by the low pressure had to manifest itself somehow - in this case by the large windfield. So while the top winds may not have been extreme - the extent of the storm created extreme damage.

[Droop12]

I agree Derek, how in the world does one gust to 137mph correlate with sustained winds of 140mph? I would associate that type of gust (considering it was the strongest gust during landfall which it probably wasnt) with winds near 110-115mph. IMO, there were probably stronger winds in a small area centered around Bay St. Louis near 125mph or so. I think some people cant comprehend how strong winds of just 74mph are. Next time your driving around 70mph or 80mph on the interstate, stick your arm out the window (carefully ) and see for yourself. Im guessing its the same effect as having winds blowing that strong. Anyways, just thought I'd share one of my wierd expirements with ya'll, have a good weekend everyone.

[Derek Ortt]

The SS category is based on 1 minute sustained wind speed, which means that an even smaller area receives the maximum winds, since just a 1 min reading of 120KT makes something a 120KT hurricane

Maybe what we could do is a mean sustained wind, along with a maximum sustained wind

[Matt-hurricanewatcher]

The SS category is based on 1 minute sustained wind speed, which means that an even smaller area receives the maximum winds, since just a 1 min reading of 120KT makes something a 120KT hurricane

Maybe what we could do is a mean sustained wind, along with a maximum sustained wind

Would that make reaching cat5 much harder...So they would become rare only the strongest like Gilbert,Allen,Mitch,Camille would be cat5s???