May 7, 2024 - Energy & Environment

Study: Hurricanes intensifying faster near coastlines amid warming

Illustration of waves crashing over a fortified coastline with swirling lines in the background and a pattern of hurricane flags in the foreground.

Illustration: Brendan Lynch/Axios

Hurricanes are intensifying more rapidly — and to a greater extent closer to shore than they used to — in large part because of human-caused climate change, a new study finds.

Driving the news: The study, published in the journal Earth's Future, found that hurricanes have on average gained strength more quickly in recent decades as they draw nearer to coastlines.

  • This impacts pricey real estate along the U.S. East and Gulf coasts and goes against previous trends of weakening near land.

Why it matters: Rapidly intensifying storms close to the coast are especially dangerous since they can leave residents with little time to prepare.

Zoom in: The past few years have featured several high-profile cases of potent storms that held their intensity as they crossed the shoreline, defying previous experience.

  • These include Hurricanes Ida, Ian, Laura and Michael in the U.S..
  • Separately, Hurricane Otis struck Acapulco, Mexico, after exploding from a tropical storm to a Category 5 hurricane in 24 hours — defying all forecast models as winds ramped up by 110 mph in just a day, per National Hurricane Center data.

How they did it: By combining historical data during the 42-year period from 1979-2020 with theory and computer model simulations, the researchers also found evidence for why this trend may have emerged and may continue.

  • Specifically, they point to reductions in vertical wind shear close to the coast, driven in part by climate change-related warming in the upper atmosphere. Also helping, the study says, is increasing humidity from rising sea surface temperatures.
  • Additionally, the researchers, which include well-known specialists on the topic of hurricanes and climate change, used various types of computer model simulations to investigate how climate change may affect key influences on hurricane intensity.
  • They also used models to project future changes in nearshore hurricane activity.

What they found: "Combined with anticipated growth of coastal population and wealth, tropical cyclones striking coastal areas are likely to result in more substantial economic losses, fatalities, and property damages during the late 21st century," the study states.

The intrigue: The paper adds to a growing literature of tropical cyclones becoming more damaging in a warming world.

  • Michael Wehner, who coauthored this study and is a researcher at Lawrence Berkeley National Laboratory, said the new data shows the need to better identify rapid intensification trends.

What they're saying: Karthik Balaguru, lead author of the study and a climate scientist at Pacific Northwest National Laboratory, said the main tropical cyclone intensification rate near the shore was 0.37 knots per six hours during the 1979-1999 period.

  • But this increased nearly three-fold, he said, to 1.15 knots per 6 hours during the 2000-2020 period.
  • "Our analysis suggests that stronger increases in relative humidity and stronger decreases in vertical wind shear are primarily responsible for these changes," he told Axios via email.
  • Wind shear occurs when winds blow in different directions and/or speeds with altitude; they can weaken or dissipate tropical storms and hurricanes.

Yes, but: The study does not indicate that every storm will intensify as it approaches land, but instead looks at aggregate trends.

  • "We are not saying that storms wouldn't weaken anymore as they approach land. Rather, the study indicates that they would weaken less or intensify more, on average," he said.

What's next: This study comes as multiple hurricane forecast groups have issued warnings about an unusually active, possibly record-setting Atlantic hurricane season, which officially begins on June 1.

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