That isn’t enough data to analyze strong cyclones globally, but we can find trends in the intensity of the weak tropical cyclones.

Here’s how: Winds transfer momentum into the surface ocean water through frictional force, driving water currents. The relationship between wind speed and ocean current, known as Ekman theory, provides a theoretical foundation for our method of deriving wind speeds from the drifter-measured ocean currents.

Our derived wind speeds are consistent with wind speeds directly measured by nearby buoy arrays, justifying the new method to estimate tropical cyclone intensity from drifter measurements.

In analyzing those records, we found that the ocean currents induced by weak tropical cyclones became stronger globally during the 1991-2020 period. We calculated that the increase in ocean currents corresponds to a 15% to 21% increase in the intensity of weak tropical cyclones, and that intensification occurred in all ocean basins.

In the Northwest Pacific, an area including China, Korea and Japan, a relatively large amount of available drifter data also shows a consistent upward trend in the intensity of strong tropical cyclones.

We also found evidence of increasing intensity in the changes in water temperatures measured by satellites. When a tropical cyclone travels through the ocean, it draws energy from the warm surface water and churns the water layers below, leaving a footprint of colder water in its wake. Stronger tropical cyclones bring more cold water from the subsurface to the surface ocean, leading to a stronger cooling in the ocean surface.

It’s important to remember that even weak tropical cyclones can have devastating impacts. Tropical Storm Megi, called Agaton in the Philippines, triggered landslides and was blamed for 214 deaths in the Philippines in April 2022. Early estimates suggest Hurricane Nicole caused over $500 million in damage in Volusia County alone when it hit Florida as a Category 1 storm in November 2022.

The 2022 Atlantic hurricane season officially ends on Nov. 30, after 14 named storms and eight hurricanes. It isn’t clear how rising global temperatures will effect the number of tropical cyclones that form, but our findings suggest that coastal communities need to be better prepared for increased intensity in those that do form and a concurrent rise in sea level in the future.

This article is republished from The Conversation, an independent nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Wei Mei, University of North Carolina at Chapel Hill and Shang-Ping Xie, University of California, San Diego. The Conversation has a variety of fascinating free newsletters.

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The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.