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Old 09-04-2005, 07:28 AM   #1
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Wind Speed Isn't Best Measure......

Portion of article from today's Tampa Tribune:

"The National Hurricane Center looks at wind speed when rating storms. Some forecasters say pressure is a better measure.

...........Atmospheric pressure, the weight of the atmosphere over a specific point on the earth, is given in millibars, a metric measurement. The lower the pressure at the surface, the more intense the storm.

Normal atmospheric pressure at sea level is roughly 1013 millibars. When Katrina made landfall, its pressure was 920 millibars.

Based on that, Katrina was as strong as Category 5 Hurricane Andrew, which demolished a wide swatch of South Florida in 1992. Andrew was 921 millibars at landfall."
"We certainly welcome other ideas in the marketplace of ideas," Hurricane Center spokesman Frank Lepore said. "Write it up then publish it and then give other scientists a crack at it. Eventually the truth comes out."


Interesting article.

Learn from the past, do not dwell on it.

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Old 09-04-2005, 07:53 AM   #2
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Re: Wind Speed Isn't Best Measure......

There is always a certain degree of unpredictability when a hurricane is still at sea and hasn't hit landfall. We were supposed to get Hurricane Dennis but it blew off into the west and didn't affect us. It's impossible to predict anything with a hurricane except that if it hits landfall there is going to be damage.

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Old 09-04-2005, 01:27 PM   #3
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I guess people can understand windspeed better than low pressure.
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Old 09-04-2005, 02:10 PM   #4
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Interesting. I've always been a real weather nerd, but I know a lot more about tornadoes and severe thunderstorms than hurricanes and tropical storms. I know the F-scale used for rating tornadoes is based strictly on the severity of damage ("The Fujita Scale is used to rate the intensity of a tornado by examining the damage caused by the tornado after it has passed over a man-made structure" There are different ground speeds and windspeeds associated with each catagory, but the rating is given based on the damage, so technically, a short-lived F5, based on ground speed, windspeed, path length, etc, could occur out in open fields, but would never receive and F5 rating because the damage would be limited to the prarie grass. In order to receive an F5 rating, the tornado must cause: "Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-inforced concrete structures badly damaged."

Katrina's pressure ratings were pretty amazing, from a scientific POV. I wish I knew more and I'm interested to know what the relationship is between the pressure and the severity of the storm, as far as the damage that would be sustained.
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Old 09-04-2005, 09:06 PM   #5
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We arrived in the Florida panhandle on July 11, the day after Hurricane Dennis had hit on the late afternoon of the 10th. Upon discovering that our condo was condemned due to the surge washing the sand out from beneath the ground floor units and thereby collapsing them and rendering the entire 3 story building untenable, we had to find a hotel room in Niceville at 10 pm that night. We got the last room available at a Hampton Inn, and it seems most of the others were occupied by a large team from the International Hurricane Research Center, based at Florida International University and operated jointly with Univrsity of Florida and Clemson University. The parking lot was full of their 4-door, 4x4 pick-up trucks full of and towing all kinds of meteorological gadgetry. It looked like a scene from the movie TWISTER (which actually deals with tornadoes, another frequent visitor down here):

The team were still up in the hotel lobby when we arrived around 11 pm, and were going over data and the next day's plan. After returning from vacation a week later, I had to look them up to see what they were up to. Their hurricane towers (which the trucks were towing) can withstand up to 200 mph winds, and measured 120 mph gusts in Navarre, near where the eyewall made landfall. Our place was over 60 miles away, which combined with the peak wind gust of (only) 120 mph, indicates that Dennis's damage was credited more to the storm surge than the wind gusts. Destin was without electricity for 3-4 days, but much of Walton, Bay, Okaloosa, Escambia and Santa Rosa Counties experienced serious beach erosion since they were still exposed from Ivan (2004) and Tropical Storm Arlene (2005). The IHRC's article is here, but I don't know if they've published a final report yet.

I doubt if the IHRC's equipment can measure pressure; I recall that is what the C-130 hurricane planes do above the eye. Dennis was one that fluctuated a bit before hitting shore and even shifted in direction a few times after re-entering the Gulf from the Florida peninsula. I'm quite thrilled my wife, brothers and neice evacuated on Saturday morning before The Menace hit on Sunday.

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