question for experts concerning saffir-simpson scale

[timNms]

http://www.aoml.noaa.gov/general/lib/laescae.html (posting a link as not to take up so much space)

On the scale, for example, for a cat one storm, with sustained winds of 74-95 mph, the damage is this: "No real damage to building structures. Damage primarly to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage"

My question is this: Wouldn't sustained winds of that magnitude for a prolonged period of time tend to cause more damage than is being claimed on the scale? The reason I ask is because during a recent storm, our sustained winds were of cat. one (according to our local met. our winds were about 95 mph sustained). Yet we had much more damage than is listed under cat one conditions. Does the scale not take into consideration wind gusts? If not, then the scale is truly misleading, correct? I mean, if one only got winds of 74-95 mph sustained and in gusts, wouldn't the damage still exceed what the scale says it would?

I'm not trying to turn this thread into a "my storm was a cat 5" kind of thing. I'm just curious to know what the pros think about this scale and if they think the damage that the scale claims a one will do is perhaps a bit misleading.

[caneflyer]

Those damage descriptions are meant only to be rough guides of typical damage. Actual damage depends on many things, such as the length of time the winds last, the variation of wind direction during an event, the gustiness of the wind, etc. Then there are non-meteorological factors like construction practices, bathymetry (for surge/wave damage), and so on.

Although Herb Saffir's original scale was based on gusts, he very quickly modified it to be based on sustained (1-min mean) winds. The scale is based on sustained wind speed only. Everything else (pressure, surge, damage) is approximate.

[SouthAlabamaWX]

Those damage descriptions are meant only to be rough guides of typical damage. Actual damage depends on many things, such as the length of time the winds last, the variation of wind direction during an event, the gustiness of the wind, etc. Then there are non-meteorological factors like construction practices, bathymetry (for surge/wave damage), and so on.

Although Herb Saffir's original scale was based on gusts, he very quickly modified it to be based on sustained (1-min mean) winds. The scale is based on sustained wind speed only. Everything else (pressure, surge, damage) is approximate.

Most wind observations are 2 min averages.

[caneflyer]

Some are, some aren't. In tropical cyclones, you can have 2 min winds from ASOS, 8 min from buoys, who knows from ships. Dropsondes measure instantaneous winds, although layer averages are used to approximate the 1 min mean. Aircraft recon winds are averaged over 10 seconds, which is meant to approximate the 1 min mean.

But most importantly, TPC's estimated storm intensity is meant to represent a 1 min mean.

[wxman57]

They're rough estimates of potential damage. Most structures should survive Cat 1 sustained winds with only damage to shingles (unless trees fall on them). What's not taken into consideration with SS is storm size and speed of movement. A large hurricane would result in a greater duration of those winds, increasing damage.

[EmeraldCoast1]

Would you rather have a 100-mile wide cat.3 moving at 12 mph come over your house or a 200-mile wide cat.1 moving at 3 mph come over your house?

After experiencing Erin, Opal, Ivan, Dennis and Katrina as well as numerous tropical storms, I may lean more toward the faster moving, smaller more intense hurricane. My unscientific observations support my theory that trees and structures (especially fences and shingles) suffer less damage with the quick, hard punches versus the relentless beating of wind for hour and hours.

Just my opinion.

[CrazyC83]

For land damage when there is no measurements to back it up, I find that the Fujita scale is better used to compare damage and potential.

[timNms]

They're rough estimates of potential damage. Most structures should survive Cat 1 sustained winds with only damage to shingles (unless trees fall on them). What's not taken into consideration with SS is storm size and speed of movement. A large hurricane would result in a greater duration of those winds, increasing damage.

I think this has been discussed before, but considering what you are saying, it appears to me that the SS scale needs to be revamped to take into consideration these things.

[brunota2003]

The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region. Note that all winds are using the U.S. 1-minute average.
Source: http://www.nhc.noaa.gov/aboutsshs.shtml

[DanKellFla]

My question is this: Wouldn't sustained winds of that magnitude for a prolonged period of time tend to cause more damage than is being claimed on the scale?

Really great question. I can't speak to the scale as a professional, but I always took it as a guide. But, I can address wind loads, buildings and damage as a Mechanical Engineer. (Disclaimer: Most of my work is with jet engines. But the laws of physics are the same everywhere.)

A short answer to your question is, "maybe." Buildings vary in construction quality so it is hard to predict damage. On bit on knowledge to remember is that wind damage increases with the SQUARE of the speed. That is:
Force= Pressure X Area
and
Pressure = P , Wind pressure (Psf), = .00256 x V^2
(V= wind speed in Mph)
The constant of .00256 changes depending on what Code you use.
Then, there is the durration of the high wind loads. A well built building could survive a fast moving Cat 3 with minor damage but a cat 1 that sits over it for 12 hours could cause a lot of damage.

As for windfield diameter, gusts, length of gusts and rainfall, I will let the pros deal with that. From the storms I have been in, one thing I have learned is that each storm is different. There are monster storms like Katrina with a huge wind field, and there are small storms like Charley that had a tiny windfield. Yet, they are classified as similar storms.

[Recurve]

One thing that I wonder about: If you are in a location where the eye of a hurricane traverses, the backside of the eye has a diffferent profile than the front. That is, winds increase somewhat gradually as the storm approaches, reaching maximum at the eyewall and then dropping suddenly as the eye is overhead. Then, when the "back" of the eye passes, you are suddenly in the eyewall with the max winds in a matter of seconds. I am not a scientist, but I believe there can be very different effects from a receiving winds that build gradually to 100 mph, and getting blasted by 100 mph winds (from the opposite direction) almost instantaneously.
For one thing, many trees in subtropical regions have evolved to take increasing winds and survive -- they shed leaves, then small branches, then larger branches, so they are never uprooted. But if they get intense winds very suddenly, they can't come apart in stages, and are more likely to be blown over.
From Wilma, I saw many Australian pines (a non-native tree) uprooted; native trees (such as mahoganies) appeared to have more damage here, with a lot of broken branches, which saved them from being destroyed completely.

[DanKellFla]

Recurve, You are correct. You are describing something called "impulse." If memory serves correct, that is equal to Force X Time. The couple of times I have been in the eye, the wind picked up fast, but not fast enough to be considered an impulse load. When something hits the floor, that is considered an impulse. A civil engineer would answer this question. My wild guess is that 30 seconds from 0 to 100 mph on a wall, while sever, is still a static load.
A pox on you Recurve. Now I will have to ask my friends at lunch on Monday. Interesting question.

As for trees. You make a good argument for planting native plants.

[Lowpressure]

One thing that I wonder about: If you are in a location where the eye of a hurricane traverses, the backside of the eye has a diffferent profile than the front. That is, winds increase somewhat gradually as the storm approaches, reaching maximum at the eyewall and then dropping suddenly as the eye is overhead. Then, when the "back" of the eye passes, you are suddenly in the eyewall with the max winds in a matter of seconds. I am not a scientist, but I believe there can be very different effects from a receiving winds that build gradually to 100 mph, and getting blasted by 100 mph winds (from the opposite direction) almost instantaneously.
For one thing, many trees in subtropical regions have evolved to take increasing winds and survive -- they shed leaves, then small branches, then larger branches, so they are never uprooted. But if they get intense winds very suddenly, they can't come apart in stages, and are more likely to be blown over.
From Wilma, I saw many Australian pines (a non-native tree) uprooted; native trees (such as mahoganies) appeared to have more damage here, with a lot of broken branches, which saved them from being destroyed completely.

Frederick did this same thing in Ocean Springs MS, 1979. Of note is that is also from the exact opposite direction, so almost a whiplash affect occurs. Rainfall does alot to tree root strength as well. Saturated soils let loose easier of trees. Also alot of damage to our house was due to debris from other homes, ie. bricks from fire places and plywood, as well as tree limbs.

[Jim Cantore]

The scale covers wind damage, It doesnt really bring surge into play, which is very misleading.

[HurricaneHunter914]

"No Real Damage"

That quote should be taken out from the description of Cat-1 winds. I've seen Cat-1 winds do bad damage before, AKA: Hurricane Ophelia-5 Million Dollars in damage-Didn't even make landfall.

[Jim Cantore]

Hurricane Ophelia-5 Million Dollars in damage-Didn't even make landfall.

Ophelia was 70 Million, Alex was 5 million although I heard it was up to 7.5

[Extremeweatherguy]

"No Real Damage"

That quote should be taken out from the description of Cat-1 winds. I've seen Cat-1 winds do bad damage before, AKA: Hurricane Ophelia-5 Million Dollars in damage-Didn't even make landfall.

yeah, they really do need to change that. Though some isolated spots saw Cat. 2 winds, most of Orlando during Charley, Miami during Wilma, and New Orleans during Katrina only recieved Cat. 1 force winds; and we all know how bad the resulting damage was in those places.

http://www.floridabaptistwitness.com/13 ... .jpg.image
^^Damage in Orlando following Charley^^

http://images.ctv.ca/archives/CTVNews/i ... 051025.jpg
^^Damage in Miami following Wilma^^

http://img168.imageshack.us/img168/5008 ... out2bo.jpg
^^Damage in New Orleans following Katrina^^