Hurricane scaling

A better way to categorize storms?

The destruction wrought by Hurricane Isaac — with its 11-foot surge, seven dead, power knocked out in half of Louisiana and nearly $2 billion in damage - has renewed debate among forecasters about how best to warn people of coming storms.

Isaac, after all, was only a Category 1 hurricane, right?

And there lies the problem. First, there’s the inadequacy of the Saffir-Simpson Scale, which ranks hurricanes on the strength of their winds from Category 1 to 5. It often fails to capture the destructive surge, as Galveston experienced during Hurricane Ike four years ago to the day on Thursday, or the inland flooding potential of a storm.

Secondly, people misuse the scale because they believe the weakest hurricanes are manageable from a risk perspective and don’t cause much damage.

“By stating that any hurricane is manageable, you underplay the potential for loss,’’ said Bill Read, the recently retired director of the National Hurricane Center. “Since this myth has been perpetuated even by us professionals, the misuse of the Saffir-Simpson Scale is now engrained in our culture.”

So what’s the point of using the ubiquitous scale?

Many forecasters and emergency managers agree that it’s because at its most fundamental level a warning scale needs to be simple.

For thunderstorms, there’s just a watch, and a warning. The same goes for tornadoes, with watches and warnings, and the Enhanced Fujita scale ranks the twister from 0 to 5 after the fact. Earthquakes go from 2.0 to 10.0 on the Richter Scale.

And in an age when people are bombarded with advertising and warning messages all day long, and they are getting their news from Facebook, Twitter, emails, text messages and short conversations with friends and neighbors, there needs to be simple messaging on hurricanes, says Tim Heller, chief meteorologist with ABC-13 TV in Houston.

“The public wants to know if it’s going to be a bad hurricane in 140 characters or less,’’ Heller said. “Like it or not, people want a very simple answer to a complicated question: Is this a bad hurricane?’’

That viewpoint is backed up by research done by political scientist Bob Stein at Rice University, who has surveyed Houston residents after hurricanes Rita and Ike to determine their attitudes toward storm preparation and evacuations.

Generally, people will not prepare for the specific threat posed by a hurricane but for the magnitude of the risk. In other words, they react to how dangerous a storm is overall, not to its specific surge, wind, power loss or inland flooding threat.

“What we’re seeing is some evidence, when you give people a generic notion of risk, they’re much more compliant and it makes the task of making a community more prepared easier,” Stein said.

He has advised Houston Mayor Annise Parker and Harris County Judge Ed Emmett to make their messages generic, to essentially say there’s a dangerous storm approaching, rather than to prepare for specific risks.

After Hurricane Ike — a Category 2 storm that nonetheless produced a devastating storm surge and damage more characteristic of a Category 4 hurricane — the National Hurricane Center removed storm surge from the Saffir-Simpson scale. It’s now based on wind speed alone.