Scientists are calling for a new Category 6 for hurricanes — because they already exist

As climate change supercharges some hurricanes, scientists are exploring how to better communicate their force to the public — including adding an extra category to reflect their power.

The current maximum on the Saffir-Simpson Hurricane Wind Scale is Category 5, which is open-ended to any storm with wind speeds greater than 252 km/h. 

A new peer-reviewed study, published Monday in Environmental Sciences, examined storm data between 1980 and 2021 and found five storms that would have been classified as Category 6 — all of them occurring in the final nine years of the study period.  

"Our intent was to draw attention to the fact that climate change is expected to make the strongest storms more intense," said Michael Wehner, climate scientist at Lawrence Berkeley National Laboratory. 

As the world warms, hotter ocean temperatures and more moisture in the air, both of which fuel hurricanes, are likely to lead to a greater proportion of intense storms, experts say. 

Research also suggests storms are getting more powerful more quickly. Another study published last fall found that tropical storms or a Category 1 hurricane were increasingly likely to develop into a Category 3 or 4 within a 24-hour period.

So far, one of the worst storms that would qualify as a Category 6 was Typhoon Haiyan in the Philippines in 2013, "which caused death and destruction at a massive scale," Wehner said. Hurricanes, typhoons and tropical cyclones are the same type of storm, only differing in where that storm develops in the world. 

Officially, Haiyan killed more than 6,000 people, although the true toll is believed to be much higher. It made landfall at wind speeds of 314 km/h, according to the U.S. Navy Joint Typhoon Warning Center. 

While most recorded storms that would fit this hypothetical category were in the western Pacific, the ingredients — hot ocean temperatures, high humidity, warm atmosphere and low wind shear — all exist in the Atlantic, too. 

"So far, there haven't been any in the Gulf of Mexico," Wehner said, "although that's certainly a place where our analysis suggests they could happen."

Beyond past storms, the study modelled and simulated the potential futures to find a "statistically significant" trend of storms that could reach this hypothetical Category 6. 

The idea has been proposed before. But experts question whether adding another hurricane category would help get across the risks of such storms.

For Tsietsi Monare, a weather presenter with Japanese broadcaster NHK World, using the Saffir-Simpson scale is only a small part of communicating the risks of these giant storms. 

"We rely a lot on pictures, videos and just simplifying the message as best as we can," Monare said, adding that he uses information on a storm's pathway, how and when it will hit certain communities and what previous typhoons have done.