The new hurricane scale doesn't take storm surge into account but includes damage estimates
The National Weather Service is using a revised Saffir-Simpson Wind Scale for the upcoming hurricane season.
The new Saffir-Simpson Hurricane Wind Scale retains the same wind speed ranges as the original but no longer addresses the potential for storm surge, rainfall-induced flooding and tornadoes. Rather, it provides the level of damage that can be expected within the five hurricane categories, along with examples of the kind of damage that may be caused.
"It's been in the works for the past couple years," says Dr. Michael Brennan, senior hurricane specialist. "Storm surges are dependent on very localized characteristics of the coastlines," he says, "not just how strong the storm is but the size of the storm and the size of the wind field."
The original Saffir-Simpson scale was created in 1971 by consulting engineer Herbert Saffir and Robert Simpson, director of the National Hurricane Center from 1967 to 1973. It was designed to tie central pressure and specific storm surge and flooding effects to each of the five hurricane categories.
"In the 1970s and 1980s, primarily central pressure was used as a proxy for intensity," says Brennan. "We did not have wind measurements from aircraft like we do now."
Brennan says NOAA decided to update the scale because storm surge values and effects are dependent on a combination of factors, including intensity, size and motion of the storm; barometric pressure; and depth of coastal waters.
NOAA compares Hurricane Ike (2008) and Hurricane Charley (2004) to highlight the discrepancy in the original scale. Ike made landfall on the upper Texas coast as a Category 2 hurricane (sustained winds of 96 to 110 mph, 6- to 8-foot surge) and produced peak storm surge values of 15 to 20 feet. Charley struck Palm Beach, Fla., as a Category 4 hurricane (sustained winds of 131 to 155 mph, 13- to 18-foot surge) but produced a storm surge of 6 to 7 feet. These values are way outside the ranges in the original scale, so a change was needed, Brennan says.
While the wind speeds within the five categories remain the same, NOAA updated the descriptions of the impact of those winds. "This was based on input from the wind engineering community and the meteorological community to better represent impacts that those types of winds would produce specifically in the United States," says Brennan.
Another change for this year is extended lead times for hurricane watches and warnings. The National Hurricane Center will issue watches and warnings for tropical storms and hurricanes along threatened coastal areas 12 hours earlier.
"A hurricane watch will be issued up to 48 hours before the onset of tropical storm force winds," says Brennan. "Anyone who lives along the coast knows there are more people to move out of the way, more traffic, and all that needs more time."
For information, visit www.nhc.noaa.gov and click on "Saffir-Simpson Scale" under "Hurricane Awareness" on the left side of the home page.
A measure of strength
(sustained winds 74-95 mph)
Very dangerous winds will produce some damage.
(sustained winds 96-110 mph)
Extremely dangerous winds will cause extensive damage.
(sustained winds 111-130 mph)
Devastating damage will occur.
(sustained winds 131-155 mph)
Catastrophic damage will occur.
(sustained winds 156-plus mph)
Catastrophic damage will occur.
This article originally appeared in the May 2010 issue.