You'll need a bigger number: Scientists consider Category 6 for the megahurricane era

In 1973, National Hurricane Center introduced the Saffir-Simpson scale, a five-category rating system that classified hurricanes according to 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 a Category 5 for disasters with winds of 157 mph or more.

In the half century since its debut, land and ocean temperatures have steadily risen due to greenhouse gas emissions. Hurricanes are becoming more intense, with stronger winds and heavier rainfall.

With catastrophic storms regularly exceeding the 157 mph threshold, some scientists say, the Saffir-Simpson scale no longer adequately captures the threat posed by the largest hurricanes.

Earlier this year, two climatologists published a paper which compared historical storm activity to a hypothetical version of the Saffir-Simpson scale that included a Category 6 for storms with sustained winds of 192 mph or greater.

Of the 197 hurricanes classified as Category 5 between 1980 and 2021, five fit the description of a hypothetical Category 6 hurricane: Typhoon Haiyan in 2013, Hurricane Patricia in 2015, Typhoon Meranti in 2016 in Sura, and Typhoon Goni in 2012.

Patricia, which made landfall near Jalisco, Mexico in October 2015, is the strongest tropical cyclone ever recorded in terms of maximum sustained winds. (While the article dealt with global storms, only storms in the Atlantic Ocean and North Pacific Ocean east of the international datum are officially rated on the Saffir-Simpson scale. Other parts of the world use different classification systems.)

Although the storm weakened to a Category 4 by the time it made landfall, its sustained winds over the Pacific Ocean reached 215 mph.

“That's a little incomprehensible,” he said Michael F. Wehner, a senior scientist at Lawrence Berkeley National Laboratory and co-author of the Category 6 paper. “It's faster than a live race car.” It's a new and dangerous world.”

In their paper, which was published in the journal Proceedings of the National Academy of Sciences, Wehner and coauthor James P. Kossin from the University of Wisconsin-Madison did not specifically call for the adoption of a Category 6, primarily because that scale is quickly being replaced by other measuring tools that more accurately measure the danger of a particular storm.

“The Saffir-Simpson scale is not as good for warning the public of impending storm danger,” Wehner said.

This category only measures sustained wind speeds, which is just one of the threats a large storm poses. Of the 455 direct U.S. deaths from hurricanes between 2013 and 2023 — a number that does not include deaths from 2017's Hurricane Maria — less than 15% were caused by wind, National Hurricane Center Director Mike Brennan said during a recent public meeting. The rest was caused by storm surges, floods and high tides.

The Saffir-Simpson scale is a holdover from earlier predictions, Brennan said.

“Thirty years ago, pretty much all we could tell you about a hurricane was how strong it was right now.” We couldn't tell you much about where it was going to go, how strong it was going to be, or what the hazards were going to look like,” Brennan said during a meeting organized by the American Meteorological Society. . “Now we can tell people a lot more.

He confirmed that the National Hurricane Center has no intention of establishing a Category 6, primarily because it is already trying to “not emphasize the extent very much,” Brennan said. Other meteorologists said it was the right call.

“I don't see the value in it at this point,” he said Mark Bourassa, a meteorologist at Florida State University's Center for Ocean-Atmospheric Prediction Studies. “There are other issues that could be better addressed, such as the spatial extent of the storm and storms, which would yield more useful information (and) help with emergency management as well as individual decision-making.”

While simplistic, Herbert Saffir and Robert Simpson's categories are the first thing many people think of when trying to understand the scale of a storm. In this sense, the persistence of the scale over the years helps people understand how much the climate has changed since its introduction.

“What the Saffir-Simpson scale is good for is quantifying and showing that the most intense storms are getting more intense because of climate change,” Wehner said. “It's not like before.”