Hurricanes slowing down in just about every ocean on Earth

Just a 10 percent slowdown doubles volume of local rainfall, a study shows

By Mark Collins - Meteorologist
Joe Raedle/Getty Images

PONTE VEDRA BEACH, Fla - A new study shows tropical cyclones are slowing down, a development that could carry huge implications for future flooding.

That research was presented for the first time Wednesday at the 33rd annual Conference on Hurricanes and Tropical Meteorology held in Ponte Vedra.

Research shows slower storms in recent years have produced heavier rainfall, according to the presentation by James Kossin of NOAA's National Centers for Environmental Information.

Hurricane Harvey, for instance, dumped record rain in Texas and underscores why speed matters when tropical systems see their pace slow to a crawl.

In fact, just a 10 percent slowdown results in double the local rain impacts. That could make flooding potentially catastrophic since storms typically slow by 20 percent over land.

Even though Harvey occurred after the study was completed, Dr. Kossin said the hurricane falls in line with the study's trend. Over 67 years of research, there was a clear slowing trend.

That trend coincides with the planet warming nearly 1 degree, and it supports growing evidence that a warming planet triggered the slowdown.

Climate change is weakening the planet's atmospheric circulation pattern, which is the mechanism that guides storm systems across oceans.

The pattern is also modifying hurricanes rain distribution. Observations indicate the heaviest rain no longer centers around the eyewall, but rather it is spread throughout the storm structure.

Slower storms have turned up in every ocean basin, except the North Indian Ocean. North of Australia has seen the greatest decrease in storm speed slowing 30%.

The implications this trend holds for future tropical rainfall are staggering. According to Dr. Kossin's calculations, rainfall becomes 20 percent heavier for nearly each degree Fahrenheit the planet warms.

As hurricanes get wetter and the overall tracks migrate poleward, hurricane flood exposure could expand to areas outside of traditionally hurricane-prone regions.

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