How Hurricane Helene quickly grew to a Category 4: NPR

Waves from the Gulf of Mexico push against the shore as Hurricane Helene rages offshore in St. Pete Beach, Florida, September 26, 2024.

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Follow The latest live updates from NPR about the impact of Helene.

In the two days before Hurricane Helene hit Florida, it developed from a relatively weak tropical storm to a major Category 4 hurricane.

When a storm becomes strong so quickly, scientists speak of rapid intensification. Such rapid intensification is relatively normal for major hurricanes that form in the Atlantic, according to federal hurricane data. For example, every Category 5 hurricane that hit the United States in the last century was a tropical storm three days earlier. according to Ken Grahamthe director of the National Weather Service.

However, there is evidence that as the planet warms due to human-caused climate change, rapid intensification of storms may also become more common. One reason for this is that storms are forming over warmer sea water than in the past because Oceans absorb much of the additional heat stored on Earth from planet-warming pollution.

Hot seawater is the fuel for hurricanes and helps them gain strength.

When Helene recovered, the water in the Gulf of Mexico was around 30 degrees Celsius – like a warm bath.

“The key ingredient in virtually all rapidly intensifying events is an incredibly warm ocean surface.” explains Jill Trepaniera hurricane climatologist at Louisiana State University.

But while many climate models suggest that storms will become more intense as the Earth warms, it is still unclear whether this trend is already underway. It is an active area of ​​research.

Unusually warm seawater also causes storms like Helene to suck up large amounts of moisture as they approach land. This moisture then falls as rain. Previous storms that caused catastrophic flooding, such as Hurricane Harvey in 2017 and Hurricane Florence in 2018, It rained more than it would without human-caused climate changescientists found out.

This story originally published as part of NPR’s live coverage of Hurricane Helene, September 27, 2024.