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hurricane's w/ gustier winds

Posted: Wed Aug 06, 2008 9:25 pm
by cpdaman
i was thinking that most of the damage in hurricane's is done in gusts.

From watching Wilma outside my front door (in a protected overhang) in pembroke pines, fl.... i was amazed at how the winds would be blowing (what i would consider strong) and then all of a sudden, it was like someone turned on the accelerator sharply and the winds force nearly doubled or tripled ( i believe a 100mph gust has much more than double the force of a 50 mph wind but anyhow).

I was wondering if there are certain characteristics that make a storm have higher wind gusts (relative to it's maximum sustained winds) because so far as i could tell it was the 5-10 second gusts that i saw which were really tearing tiles and roofing up. Not saying that wilma was a particular gusty hurricane because i haven't been in that many (but i do remember it being more gusty than hurricane jeane. And also i find this significat because it seems the higher gusts are what we have to watch out for, especially

Re: hurricane's w/ gustier winds

Posted: Thu Aug 07, 2008 4:41 pm
by Aslkahuna
The average gust ratio for a storm once over land is much higher in the 1.5-1.6 range thus for 100 mph sustained winds it's possible to get gusts of 150+ mph. The key to the gustiness lies in what the storm is doing at landfall. If you have a storm that is intensifying then the gusts will be higher since the stronger convection will surface the stronger winds easily. Weakening storms tend to be less gusty since the convection has already weakened and surfacing is not as effective.

Steve

Posted: Sat Aug 23, 2008 9:49 pm
by DanKellFla
Vp = 0.6V² is a generic equation (metric) describing the pressure from wind. Vp is the pressure. V is the wind velocity. As you can see, the pressure increases with the SQUARE of the wind velocity. Doubling the wind speed increases the pressure 4 times.

Posted: Sun Aug 24, 2008 2:56 pm
by Cyclenall
So the basic idea is how gusty (in frequency) and how strong the gusts are depends on what changes to the TC are occurring at the time? Does the growth in size affect how gusty a tropical cyclone is?

Posted: Mon Aug 25, 2008 7:02 pm
by DanKellFla
I am not educated in weather, so, I will leave the question about TC growth and gusts to the professionals. But, I am an engineer. (At least I play one in my cube every day.) The idea that most of the damage comes from gusts over simplifies the situation in a storm. Now, I am going to simplfy things some more. Hopefully, this will help.
Wind loading happens in two ways, a gust or a gradual increase in wind speed. A gradual increase in wind speed will allow a building to tolerate a higher wind load than a sudden increase. All things being equal, what you observed with gusts causing most of the damage is true. Of course, all things are not equal. All storms are different. Some storms have higher steady winds than others. Some are gustier than other storms. Damage to a building has a lot to do with the quality of its initial construction as well as the quality of nearby buildings.


I could go on and on about this. There is a whole other concept that has to do with vibrations on large flat panels that I could talk about. But, I won't. It is really dull and I don't feel like writing equations. Suffice to say, winds can induce vibrations in a structure that causes self destruction.

Nothing is simple..... Sorry if I babled on too long.