Time to rethink hurricane categories
Louisiana state climatologist Barry Keim says it’s time for people to stop thinking of Category 1 hurricanes as less dangerous than storms of higher wind categories.
Two of the hurricanes that slammed into the U.S. mainland this year — Hurricane Isaac in southeast Louisiana and Hurricane Sandy on the East Coast — caused major damage, but they were “only” Category 1 storms.
The only “major hurricane” of this hurricane season, which ran from July 1 through Nov. 30, was Hurricane Michael, a Category 3 storm that clocked winds of 115 mph but stayed out at sea.
The 2012 hurricane season, from July 1 to Nov. 30, certainly was a busy one, surpassing forecasters’ expectations by producing 19 named storms, of which 10 became hurricanes.
“This is a third year in a row with 19 named storms,” Keim said.
The August forecast update from the National Oceanic and Atmospheric Administration’s Climate Prediction Center had called for between 12 and 17 named storms, with five to eight of those becoming hurricanes and two to three of those becoming “major hurricanes” with winds of 111 mph or more.
Despite the large number of storms, there hasn’t been a major hurricane with winds of 111 mph or more that has made landfall in the U.S. since 2005, when hurricanes Katrina and Rita, both Category 5 storms, devastated south Louisiana. Keim said that makes seven consecutive years of no U.S. landfall of a major hurricane, beating the record of the previous longest stretch, five years without a major hurricane.
One reason forecasters thought there would be fewer named storms this year was because of the forecast that there might be an El Niño climate pattern, which hampers the formation and strengthening of storms in the Atlantic Ocean.
“But, that El Niño never happened,” Keim said.
But that didn’t mean the U.S. got away free this hurricane season.
“The two Category 1 storms we had this year were major in their own way,” Keim said.
Hurricane Sandy, which caused widespread devastation on the East Coast, was an unusual storm because of its size, the damage it caused and the track it took, which kept it over water for most of the storm’s trip up the coast. Tropical storms draw energy from the water, so the extended time over the water allowed Hurricane Sandy to generate a large storm surge.
“This was so far out of line with what is expected with a Category 1,” Keim said. The National Weather Service stopped connecting a particular storm surge to a category of storm several years ago because the Saffir-Simpson scale of categories counts only a storm’s wind speed, and much more than that goes into figuring out the height of a storm surge.
In a similar way, Hurricane Isaac surprised some people by the large storm surge it pushed into southeast Louisiana because “it was only a Category 1 storm.”
Under the old Saffir-Simpson scale, a Category 1 storm was said to produce between a 4-foot and 5-foot surge, but Hurricane Isaac pushed 13 feet of surge into some areas of the coast, Keim said.
The Saffir-Simpson scale, he said, tells people nothing about the size of the storm or the geography over which the storm will pass, which is important for storm surge.
So, some new thinking is in order.
“I think we’re all somewhat guilty of saying, ‘Well, this is only a Category 1 hurricane,’ ” Keim said.
Amy Wold is the environmental reporter with The Advocate. She can be reached at firstname.lastname@example.org. Follow her on Twitter @awold10.