Sunday, August 28, 2005

Kat 6...

Mr. Atos

As Hurricane Katrina approaches the Lousianna coast with maximum sustained winds of 175 mph, The Mayor of New Orleans has ordered the immediate evacuation of the entire city.

NEW ORLEANS - Mayor Ray Nagin ordered an immediate evacuation Sunday for all of New Orleans, a city sitting below sea level with 485,000 inhabitants, as Hurricane Katrina bore down with wind revved up to nearly 175 mph and a threat of a massive storm surge.

Acknowledging that large numbers of people, many of them stranded tourists, would be unable to leave, the city set up 10 places of last resort including the Superdome arena.

"This is a once in a lifetime event," the mayor said. "The city of New Orleans has never seen a hurricane of this magnitude hit it directly."

The mayor called the order unprecedented, but said Katrina's storm surge would likely top the levees that protect the city from the surrounding water of Lake Pontchartrain, the Mississippi River and marshes. The bowl-shaped city must pump water out even during normal times, and the hurricane threatened pump power.

In a scene reminiscent of Deep Impact, News images show thousands of cars jammed into the outbound lanes of the interstates. Rumor has it that the President himself ordered local authorities to issue evacuation orders, breaking the paralysis of political fear in the face of approaching danger.

Some are pegging this storm as a Category 6, suggesting it to be a monster beyond anything seen since a similar behemoth snuck out of the Gulf and pounced on Galveston in 1900. Either way it goes at this point Katrina will be a killer. With landfall expected early Monday morning, the August Gulf will only continue to lend her strength. God help them.

Here are a few links for those interested or concerned:

Live Storm Thread
Live Storm Analysis
NOAA Storm Data
Lousianna State Police (Info, Shelters, and Evac Routes)

The worst is upon Louisianna as Kat's eye approaches shore along the delta. She is a firm cat 5, with sustained winds in excess of 160 mph. Feeder band thunderstorms are gusting in excess of 60 miles an hour and already dumping a fair amount of rain. Expectations are that only around 50% of area residents have actually evacuated. Hugh Hewitt links to a frightening warning from AP News.

Estimates have been made of tens of thousands of deaths from flooding that could overrun the levees and turn New Orleans into a 30-foot-deep toxic lake filled with chemicals and petroleum from refineries, and waste from ruined septic systems.

The storm looks to be approaching slightly to the left of the city which would slam the peak surge of the anti-cyclonic circulation directly up the mouth of the Mississippi delta. The storm surge could be in excess of 30 feet before the torential area rains are even a factor. This looks to be catastrophic. Lets hope for the best and expect the worst.

The impact looks to be felt nationwide as a major portion of U.S. oil production in this region of the Gulf is expected to be shut down if not, in fact, decimated by this storm. Bloomberg suggests the pain at the pump will be immediate and will hit the nation even as Kat's eye hits land in the morning.

Additional links:
Josh Britton
New Live Thread
Live Local News Feed - WWL

Dr. Jeff Masters posts a very interesting overview of the consequences of Kat's landfall. But, this point in particular caught my attention.

High rise buildings may offer good refuge, but Katrina has the potential to knock down a high-rise building. A 25 foot storm surge and 30 - 40 foot high battering waves on top of that may be able to bring down a steel-reinforced high rise building. I don't believe a high rise building taller than six stories has ever been brought down by a hurricane, so this may not happen Monday, either. We are definitely in unknown waters with Katrina.
In building design, wind loads are considered similar to earthquake loads in the calculation of lateral forces for resistance. Most people realize that a building is designed to withstand vertical gravitional forces. It is built to stand up. But, a building is also designed like a cantilevered beam meant to resist lateral forces, such as wind and vibration. When a tower is designed, the maximum sustained wind taken from historic data assembled with charts provided in the applicable building code, is applied across the face of the building to calculate it's overturning moment. The building is then designed structurally to resist that moment. The wind speeds accompanying Katrina could be in excess of the maximum known winds for the towers designed in New Orleans. The lateral forces presented by this storm could very well be in excess of the resisting moments of these buildings. Add to that the additional force of waves battering the lower floors and the danger is exponentially worse.

Understand this. In structural design for lateral loads in modern buildings, maximum wind loading is never, repeat never, considered in conjuntion with a seismic event. The odds are so great against the possibility that it is simply not required. Combine sustained winds in excess of the maximum design load, with lateral wave loads striking the building in similar fashion to a seismic event, and there is a very real possibility of building collapse during this storm... ESPECIALLY highrises. I repeat, catastrophic building failure is a very real possiblity.

I will supply supporting references in future updates, but do take this into consideration. I'm no storm expert. But, I do design buildings for a living.

New Orleans NOAA Weather Radio
Baton Rouge Radio (Live Coverage)
New Live Thread
NOAA Weather Radar for New Orleans

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