In 1973, the National Hurricane Center introduced the Saffir-Simpson scale, a five-category rating system that classified hurricanes by wind intensity.
At the bottom of the scale was Category 1, for storms with sustained winds of 74 to 95 mph. At the top was Category 5, for disasters with winds of 157 mph or more.
In the half-century since the scale’s debut, land and ocean temperatures have steadily risen due to greenhouse gas emissions. Hurricanes have become more intense, with stronger winds and heavier rainfall.
This week, a research team at the University of Pennsylvania led by climate scientist Michael Mann predicted that the North Atlantic will see an unprecedented 33 named tropical cyclones from June 1 to Nov. 30.
Some scientists argue that with catastrophic storms regularly blowing past the 157-mph threshold, the Saffir-Simpson scale no longer adequately conveys the threat the biggest hurricanes present.
Earlier this year, two climate scientists published a paper comparing historical storm activity to a hypothetical version of the Saffir-Simpson scale, including a Category 6, for storms with sustained winds of 192 mph or more.
Of the 197 hurricanes classified as Category 5 from 1980 to 2021, five fit the description of a hypothetical Category 6 hurricane: Typhoon Haiyan in 2013, Hurricane Patricia in 2015, Typhoon Meranti in 2016, Typhoon Goni in 2020, and Typhoon Surigae in 2021.
Patricia, which made landfall near Jalisco, Mexico, in October 2015, is the most powerful tropical cyclone ever recorded in terms of maximum sustained winds.
(While the paper looked at global storms, only storms in the Atlantic Ocean and the northern Pacific Ocean east of the International Date Line are officially ranked on the Saffir-Simpson scale. Other parts of the world use different classification systems.)
Though the storm had weakened to a Category 4 by the time it landed, its sustained winds over the Pacific Ocean hit 215 mph.
“That’s kind of incomprehensible,” said Michael F. Wehner, a senior scientist at the Lawrence Berkeley National Laboratory and co-author of the Category 6 paper. “That’s faster than a racing car in a straightaway. It’s a new and dangerous world.”
In their paper, which was published in the Proceedings of the National Academy of Sciences, Wehner and co-author James P. Kossin of the University of Wisconsin–Madison did not explicitly call for the adoption of a Category 6, primarily because the scale is quickly being supplanted by other measurement tools that more accurately gauge the hazard of a specific storm.
“The Saffir-Simpson scale is not all that good for warning the public of the impending danger of a storm,” Wehner said.
