Tropical Storm Aletta grows stronger in Pacific

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Tropical cyclones have generally slowed more in the Northern Hemisphere where they are also known as hurricanes and typhoons and where more of these storms typically occur each year. While this sounds like good news, it isn't: It's not that hurricanes' wind speeds are diminishing, but instead how fast the entire storm moves, a new study reports.

In the wake of Hurricane Harvey's torrential rains, which dumped several feet of water on sections of Houston, Texas, last August, scientists showed that warmer sea and air temperatures pumped more moisture into the storm-which then fell as rain.

In the western north Pacific, the slowdown's been 30 percent; in the "Australian" region it's 19 percent. But when Atlantic storms hit land - like Harvey did in 2017 - the study said the slowdown is a significant 20%.

Study author James Kossin of the National Oceanic and Atmospheric Administration says Harvey is a great example of what he found.

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Experts believe that continued global warming will increase the severity of tropical storms, but they also believe this anthropogenic warming will increase rainfall.

The globe's hurricanes have seen a striking slowdown in their speed of movement across landscapes and seascapes over the past 65 years, a finding that suggests rising rainfall and storm-surge risks, according to research reported Wednesday.

Christina Patricola, a scientist with the climate and ecosystem sciences division of California's Lawrence Berkeley National Laboratory, called Kossin's work "important and new" and says she found it "pretty convincing".

The trend has all the signs of human-caused climate change, Kossin said.

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"Kossin is right that a 10 percent change in tropical cyclone motion would be an important change due to its effect on accumulated precipitation", Texas state climatologist John Nielsen-Gammon said in an email.

The result is more rainfall and more damage to buildings as hurricanes hover over population centers for longer periods of time.

"What we're seeing nearly certainly reflects both natural and human-caused changes", Kossin said.

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