Kudos to Derek Ortt and Daniel Stern for recognizing Katrina

[Stormcenter]

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

Question: How long would it take for the storm surge 'bulge', along with wind-formed waves, to recede after the hurricane drops its winds to a lower category?

I've wondered if there is any accurate way to estimate this, as a storm like Katrina brings the problems to light. Katrina was at one point a strong Cat 5 storm, and during much of her approach to land was still a strong Cat 4 storm. So over the several days that she churned through the gulf at Cat 5 or 4, and considering the large size of the storm's hurricane windfield, she built up a high cat 4 to cat 5 storm surge.

So if hours before landfall, the hurricane's winds were measured at Cat 3 strength, meaning she downgraded just before hitting land, would it not take much more time for the seas ahead of her to 'calm' to a level more appropriate to a smaller storm?

It seems like Katrina downgraded her windspeed before striking land, but her surge was still at Cat 4 level or more as it pushed up on shore. Combined with the shallow ramp up on the gulf coast and the high tide, the surge seemed to be equal to a Cat 4 or 5 storm.

And though New Orleans experienced no more than Cat 1 winds, wouldn't they too have been fecing the effects of a far stronger surge? A ripple travelling across a pond does not greatly diminish in height as it travels...the degredation of strength, speed and height is much slower in water than in air. So despite Katrina's Cat 3 deintensification, it would seem logical to conclude that much of the Mississippi coast received high cat 4 or cat 5 surge, and New Orleans' lakes and canals were bulged by surge of at least Cat 3.

Any opinion?

I still have serious doubts despite what the NHC has stated Katrina's winds were "only" category 1 in the New Orleans area. What she did to the Superdome's roof and other areas around the region were not done by cat. 1 winds. IMO

[wxmann_91]

The winds on the Superdome roof were probably one category higher than the winds at the surface. That would mean that the Superdome roof experinced winds of borderline Cat 2/Cat 3 strength. Certainly possible.

All in all, IMO much of greater New Orleans probably experienced winds of borderline Cat 1/Cat 2 strength, and of course winds at the tops of buildings could be one category stronger. I didn't see any damage windwise that would correlate to anything stronger than that.

[senorpepr]

I still have serious doubts despite what the NHC has stated Katrina's winds were "only" category 1 in the New Orleans area. What she did to the Superdome's roof and other areas around the region were not done by cat. 1 winds. IMO

You can't quite compare the surface winds to what occurred to the top of the Superdome. The winds at 10m is much lower than those at the top of the Superdome at 82m.

Just to give you an idea...
Say a 10m wind of 65kt was recorded. At 35m, it would be expected for the winds to be 80kt. Just in that small difference in altitude, we have gone from a minimal category one to a maximum category one... and that's only a difference from 10m to 35m. It was VERY possible for 10m winds to only be of category one intensity and have category two and three winds at the rooftop of the Superdome. Therefore, it is EXTREMELY possible for "cateogry one" winds to do that much damage to the Superdome.

This is yet another reason why vertical evacuation is dumber than Jessica Simpson's knowledge of tuna.