In Case Of Emergency, Read Blog

With storm season beginning in earnest and the first named Atlantic hurricane heading towards the Texas coast, I thought I would mention that the National Oceanic and Atmospheric Administration has altered the way it will report the five-category Saffir-Simpson Wind Scale eliminating estimates on storm surge and inland flooding from rainfall.

According to an Associated Press story by Jennifer Kay in USA Today:

The scale was changed to alleviate confusion over storm surge and flooding predictions that didn’t match what actually happened as a hurricane made landfall, said Chris Landsea, science operations officer at the National Hurricane Center and leader of the team that made the changes.

The new scale still classifies hurricanes by maximum sustained wind speeds, starting at 74 mph with Category 1. Category 3 and above is considered a “major hurricane,” and the strongest with winds greater than 155 mph is Category 5.

More importantly, it tells people how strong a storm it will take to bring down the trees, fences, power lines and walls around them. The damage descriptions to homes, shopping centers and industrial buildings are more specific than the previous version and updated to reflect more coastal development.

Hurricane Alex approaches land as seen from a NOAA satellite photo (Associated Press)

Officials hope the new approach will alleviate public confusion:

The revised Saffir-Simpson scale eliminates references to flooding caused by rain and estimates for storm surge, or the mound of seawater pushed ahead by a hurricane’s winds. This simplifies the scale and shows that forecasters now have a better understanding of how storm surge works, said Florida’s state meteorologist, Amy Godsey. The problem with the previous version was how inconsistent it proved to be when it came to storm surge, she said.

For example, a compact Hurricane Charley made landfall in 2004 in southwestern Florida with Category 4 winds, but it had the storm surge previously expected from a much weaker hurricane. A very large Hurricane Ike made landfall just outside Galveston, Texas, in 2008 as a Category 2 hurricane with a storm surge of 15 to 20 feet a peak associated with a Category 4 or 5 hurricane on the old scale. If Ike made landfall in Daytona Beach, it only would have produced a storm surge around 8 feet, Landsea said.

On the U.S. Atlantic coast, the deep waters offshore produce a smaller storm surge than the more shallow Gulf of Mexico.

“It’s like the difference between having a plate full of water and a bowl full of water,” Landsea says. “Put a fan next to them, and the water will be pushed off the plate, but the water will just swirl around in the bowl.”

…Storm surge and flooding forecasts will remain in hurricane advisories and statements issued by the National Hurricane Center and local National Weather Service offices.

The hurricane center is considering adding a storm-surge warning to its list of watches and warnings during hurricane season. Sometimes places outside the cone of a hurricane warnings can still be vulnerable to storm surge, hurricane center director Bill Read said. No decision on adding storm-surge warnings will come for another two or three years.

The revision to the Saffir-Simpson scale took more than a year. Five wind engineers submitted updated descriptions of wind damage, and a draft was released for public comment last year. It’s the first update to the scale since barometric pressure was removed from it about a decade ago, Landsea said.