Hurricanes slow their roll around the world

By Giorgia Guglielmi

Sluggish hurricanes have become increasingly common over the past 70 years, according to a new study. Storms that linger over a given area for longer periods, such as Hurricane Harvey, which stalled over eastern Texas for almost a week in August 2017, bring more rain and have greater potential to cause damage than ones that pass quickly. Scientists aren’t sure why this is happening, but if the trend continues, future hurricanes could be even more disastrous.

The study1, published on 6 June in Nature, is the first to analyse hurricane speeds globally. It finds that the speed at which tropical cyclones moved across the planet slowed by about 10% between 1949 and 2016. The storms travelled at more than 19 kilometres an hour on average in 1949, compared with an average speed of about 17 kilometres an hour in 2016. The effect was significant over land, with cyclones affecting regions along the western North Pacific slowing by 30% and by about 20% over Australia and landmasses in or near the North Atlantic.

“That’s a big signal,” says study author James Kossin, a climate scientist at the US National Oceanic and Atmospheric Administration’s (NOAA) Cooperative Institute for Meteorological Satellite Studies in Madison, Wisconsin. After studies suggested that atmospheric circulation patterns in the tropics might be slowing as a result of global warming2, Kossin set out to see whether hurricanes, which are carried along by these wind currents, also put on the brakes. “I’m not sure that I was quite prepared for the amount of slowing that I did find,” he says.

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