Measuring hurricanes

The venerable Saffir-Simpson scale for measuring hurricane strength is so simple to use, it's not really adequate for the task of assessing risk and estimating damage.

"If I could wave a wand and make it go away, I would," said Bill Read, at the National Hurricane Conference in Austin on Friday. "It made sense in the era it was conceived, four decades ago, and now it's ingrained in the culture."

Attendees at the hurricane center have buzzed about the Saffir-Simpson scale's inadequacies.

KHOU-TV's chief meteorologist Gene Norman said it needs to be modified to better account for surge.

Greg Bostwick, a meteorologist at KFDM-TV in Beaumont, said his viewers couldn't believe how "only" a Category 2 storm striking 90 miles away could flood one-third of Orange County.

Some hurricane scientists, such as Mark Powell of the National Oceanic and Atmospheric Administration's Hurricane Research Division, have been arguing in recent months to replace the Saffir-Simpson scale entirely.

Powell said the scale is especially deceptive when it comes to storm surges, and when you review the data there's simply no correlation between the category of a hurricane and the amount of land it inundates.

[...]

Based upon maximum sustained winds, the scale ranges from Category 1, the weakest hurricane classification, to the fearsome and rare Category 5, with winds greater than 155 mph.

But the scale fails to take a host of factors into account -- such as physical size and rainfall potential -- that are critical to determining whether a particular storm will have a large surge or cause inland flooding, like Houston experienced during Tropical Storm Allison in 2001.

No big surprise here. The Saffir-Simpson scale is essentially one-dimensional, so of course it can only capture so much information in it. I'm a little incredulous that anyone who watched any of the Ike coverage from last year could have seen the satellite pictures showing just how massive it was and not imagined how much havoc it would wreak. Having said that, the words "at least it's just a Cat 2" escaped my lips more than once during the run-up. Perhaps another number, one that's more evocative than just a storm surge size, would help. If we can replace the Richter scale with something better, surely we can do it for the Saffir-Simpson as well.

Posted by Charles Kuffner on April 12, 2009 to Hurricane Katrina