Pressure, Not Wild Speed, Is Better Judge Of Hurricane Destruction, Study Says

Superstorm Sandy wasn't even considered a hurricane when it drowned New York City in 2012, and 2005's Katrina was a Category 3 despite a punch that cleaved homes from foundations along the Gulf Coast, but a new scale proposed by a leading researcher would have elevated the systems to a 4 and 5, respectively, ahead of landfall.

Colorado State University scientist Phil Klotzbach is the lead author of a paper published online last week by the Bulletin of the American Meteorological Society that found the minimum central surface pressure of a tropical cyclone is a better indicator of potential storm damage than wind speed.

Air pressure inside a hurricane is a measure of the storm's intensity, the amount of power in the vacuum formed by winds roaring toward the eye. The lower the pressure, the stronger the storm, but pressure isn't always aligned exactly with how fast the winds are moving.

Swelling storms, those expanding and covering more area, can experience slowing wind speeds but still have low central pressure. That means large storms might get downgraded based on wind speed but maintain the intensity to push a devastating storm surge ashore -- a killer responsible for about half of the hurricane-related deaths between 1963 and 2012, according to the National Hurricane Center.

"I'm guessing people will say that the public doesn't understand pressure, but that they do understand wind," Klotzbach said. "But I don't think people really understand wind."

The decades-old and deeply ingrained Saffir-Simpson Hurricane Wind Scale has been criticized for years for not telling the whole story of a storm. Its 1 to 5 ranking system leaves out storm-surge dangers and torrential rainfall threats.

While Klotzbach's study, which looked at landfalling hurricanes between 1900 and 2018, doesn't address rainfall, it shows a closer correlation between the damage wrought by a storm and its minimum central pressure.

Hurricane Michael would have been a Cat 5 under this scale

Under Klotzbach's pressure-based scale, 2018's Hurricane Michael would have gained Category 5 status ahead of reaching the coast. The powerful storm that wiped out Mexico Beach, Fla. and cut a path of devastation into Georgia, was considered Cat 4 at landfall. A reanalysis of storm data elevated it to a Cat 5 six months after its October landfall.

Sandy was considered a post-tropical cyclone at landfall, but its central pressure of 942 would have made it a Cat 4 storm on Klotzbach's scale.

Hurricane Ike in 2008 was a Cat 2 hurricane when it hit the north end of Galveston Island, Texas, where more than a dozen people died as a 20-foot storm surge pushed ashore. Ike would have been a major Cat 3 hurricane under Kloztbach's scale.

"Ike was a Cat 2 so people said 'we're not going anywhere,'" Klotzbach said.

More hurricanes gained categories when considering pressure, but some were deflated. Barry, which hit Louisiana in July 2019, lost its hurricane status.

James Franklin, the former chief of forecast operations at the National Hurricane Center, said he's not surprised pressure is a better indicator of storm damage, but he's not ready to scrap the Saffir-Simpson scale.

While insurance companies might want to use pressure as a guide, it doesn't help the general public in understanding what is coming, Franklin said.

"People in harm's way need to be concerned with the potential threats to themselves and their property -- that is wind, surge flooding and freshwater flooding," he said. "Emphasizing the minimum central pressure, or changing the categorization from wind to pressure, would be counterproductive to communicating these risks to residents."

Some are reluctant to give up on the Saffir-Simpson scale

The National Hurricane Center has emphasized risks over storm category for years, but officials are reluctant to talk about potential changes or alternatives to the Saffir-Simpson scale, which launched in 1973. Storm surge was included in the scale originally, but was removed in 2010.

The hurricane center now issues specific storm surge watches and warnings individualized for each storm and coastline.

"People are expending a lot of energy trying to improve the Saffir-Simpson scale and I think these efforts are misguided," Franklin said.

Some studies have looked at measuring storms by integrated kinetic energy, which considers the size of the storm as well as wind speed. In 2013, a paper by researchers at Florida State University and the Florida Climate Institute proposed a measurement that includes size, intensity and duration.

Jeff Masters, co-founder of Weather Underground who writes the Eye of the Storm blog for Scientific American, thinks a change to Saffir-Simpson is warranted. He said Europe uses a color-coded system to convey magnitude of the storm threat, but acknowledged that may be too simple.

"Clearly we have to do something different because the current system does not work," Masters said about the Saffir-Simpson scale. "The paper makes a good case that using central pressure to rank hurricanes is superior to using maximum winds."

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