The prior month, Hurricane Lee, a major hurricane currently traveling up the Atlantic, meteorologists observed the third-fastest case of rapid intensification ever recorded. On September 7, wind speeds inside Lee more than doubled, boosting it from an 80 mph Cat 1 storm to a terrifying 165 mph Cat 5 storm.

Rapid intensification only crops up in a handful of tropical cyclones each year. However, a study published last year in Nature found that, within 240 miles of coastlines, rapidly intensifying storms are now significantly more common than they were 40 years ago. Examples include Hurricane Ian in 2022 and Hurricane Michael in 2018. The latter leapt from a Category 2 storm to Category 5 the day before making landfall in the Florida panhandle. It claimed dozens of lives and caused $25 billion in damage.

And while some hurricanes intensify over open water, those that grow rapidly before striking landfall pose a major risk to people living on the coast. In such a situation, evacuations ordered under the expectation of, say, a Category 2 or 3 storm could prove wholly inadequate, leaving thousands of people vulnerable—a meteorologist’s worst nightmare.

Large, major storms like Milton and Helene also threaten people further inland; as Helene moved north, it caused catastrophic flooding over North Carolina and parts of the U.S. southeast.

Until very recently, it’s been difficult to forecast rapid intensification, which can emerge suddenly, partly because so many shifting conditions need to align in order to trigger it. Plus, much depends on activity in the very core of the hurricane, from where it is notoriously difficult to gather data. Scientists are now developing new methods to help them warn people of this rising threat.