Category 6 Hurricanes? They've Happened

May 21, 2006 — -- There is no official Category 6 for hurricanes, but scientists say they're pondering whether there should be as evidence mounts that hurricanes around the world have sharply worsened over the past 30 years -- and all but a handful of hurricane experts now agree this worsening bears the fingerprints of man-made global warming.

In fact, say scientists, there have already been hurricanes strong enough to qualify as Category 6s. They'd define those as having sustained winds over 175 or 180 mph. A couple told me they'd measured close to 200 mph on a few occasions.

The Saffir-Simpson hurricane category scale is based on wind speed: A Category 1 hurricane has sustained winds from 74 to 95 mph, Category 2 has sustained winds from 96 to 110 mph, Category 3 has sustained winds from 111 to 130 mph, Category 4 has sustained winds from 131 to 155, and a Category 5 storm has sustained winds greater than 155 mph.

The categories run in roughly 20 mph increments, so a Cat 6 would be greater than 175 or 180 mph.

To put this all in perspective, Katrina was a Category 5 hurricane out over some hot spots in the Gulf. But when it hit New Orleans, scientists now know, Katrina had winds at a low Category 3, and much of them Category 2, including the "left side winds" that then came down from the north and pushed the surge-swollen waters of Lake Pontchartrain over and through NOLA's levees. (Hurricanes spin counterclockwise in the northern hemisphere, so when Katrina came ashore just east of New Orleans, its winds hit the city from the north.)

Only three Category 5s have come ashore in the United States in the past century -- the 1935 Labor Day Hurricane, Camille in 1969 and Andrew in 1992.

But because of man-made global warming, most hurricane scientists say now we will probably be getting Category 4 and 5 hurricanes more frequently in the coming decades.