Warming Powering Stronger Hurricanes, While Making Their Behavior Far More Unpredictable

Fuelled by heat from ocean waters, hurricanes are sometimes known as nature's steam engines. As they barrel over the oceans, they turn its heat into brutal kinetic energy that flattens islands and inundates coastal cities, taking months of urgent repair work to heal. Ocean temperatures are now breaking all records, and these "engines" are responding accordingly, cutting different paths across the ocean, slowing down, and becoming less predictable and more dangerous. Now there's a race to understand exactly how hurricanes are rewriting the rules and patterns we've seen before, in the hope of learning how we can adapt.

There's a distinct seasonal cycle to hurricanes in the Atlantic, with very few or none at all in winter, and a peak in September. A strong, early start to the hurricane season is in line with what we would expect with climate change, says James Kossin, a climate and atmospheric scientist retired from the US National Oceanic and Atmospheric Administration (NOAA). "Hurricanes themselves just respond to the environment that they're sitting in," Kossin says. "And so if you make the environment in June look like the environment that would normally be in August or September, then the hurricanes will simply behave as though it's August or September. They don't have a calendar."

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One of the strongest storms to form recently in the Atlantic did so under conditions that ought to have prevented a hurricane from forming, says Hugh Willoughby, research professor in earth and environment at Florida International University. In September 2023, at the peak of the Atlantic season, Hurricane Lee rapidly intensified into a category five storm. At the time, an El Niño was in effect, which generally has a stifling effect on storms in the Atlantic due to greater wind shear and atmospheric stability.

"Shear is death for hurricanes," says Willoughby. Vertical wind shear is the change in wind speed and direction at different heights – high wind shear disturbs the structure of a hurricane. "Imagine you've got a turbine engine – shear knocks some of the blades out," says Willoughby. So for a category five like Hurricane Lee to form despite considerable shear came as "a nasty surprise". The extraordinary ocean warmth in September 2023 may have somehow overwhelmed the influence of shear, says Willoughby, though it's not entirely clear why.

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https://www.bbc.com/future/article/20240712-modern-hurricanes-are-rewriting-the-rules-of-extreme-storms