Hurricane Dorian, which devastated the Bahamas this summer, could have been a Category 6.
Or at least that's an argument made recently by Weather Underground co-founder and meteorologist Jeff Masters. If the traditional Saffir-Simpson scale of hurricane intensity were extended to its next logical step, Dorian, with winds reaching 185 miles per hour, would have qualified for the new category.
The reasoning, laid out in a recent article by Masters, focuses heavily on the impacts of climate change, which leading scientists say is changing tropical cyclones in a number of ways.
Among those changes are more-intense cyclones, storms that may drift farther north, and wetter storms that devastate areas far inland with flooding. There has been no strong proof, however, that there will be more hurricanes in total as global average air and sea temperatures rise.
"My argument is that strictly from a climate change communication point of view, it would be valuable to have a Category 6," Masters said in an email. "That alone is not enough justification to add one, though."
Indeed, many weather scientists and communicators agree that an additional category misses the point.
A Category 5 storm, which earns the designation when winds breach 157 miles per hour, is considered so destructive that there's no use in adding another step. The National Hurricane Center, the federal office that produces benchmark forecasts for tropical weather, says damage from such a storm would be catastrophic, leaving many framed homes destroyed, power out for weeks or months and fallen trees and power lines cutting off residential areas.
"Any landmass hit by a Category 5 hurricane is devastated," said Phil Klotzbach, of the Tropical Meteorology Project at Colorado State University. "Whether it is Dorian in the northwest Bahamas, Michael in the Florida Panhandle, or Irma on several different Caribbean islands, the rebuilding process from a Category 5 hurricane takes years."
Klotzbach added that another step seemed "unintuitive," and that if a Category 6 were added, "people might respond, 'well, it's a Category 5, but at least it's not a Category 6.'"
Researchers in South Carolina have established in the past that many people already ignore evacuation orders for low-category storms.
There are many more criticisms of the Saffir-Simpson Scale, which since 2010 has been based solely on a storm's sustained wind speed. The scale thus ignores other major threats from hurricanes: storm surge, or the water pushed onto land by an oncoming storm, and freshwater flooding generated when a hurricane dumps water inland.
The second problem has been a particular threat to South Carolina after Hurricanes Matthew and Florence, in 2016 and 2018, respectively. It's a challenging one for emergency officials, because unlike with storm surge, it's not always clear where flooding may happen and who should be evacuated in advance.
"There is certainly room for improvement on the current scale," Klotzbach said.
But, at least for now, the traditional scale of Category 1 to 5 is here to stay, in part because the Hurricane Center doesn't agree with adding another step.
"I agree that it is a moot point, since there is no support for it from NHC, and they would have to spearhead such an effort," Masters said.