Hurricanes Are Declining, and That's Bad News
While hurricanes batter coastal regions with destructive wind speeds, study author James Kossin says the speed at which hurricanes track along their paths -- their translational speed -- can also play a role in the damage and devastation they cause. Their movement influences how much rain falls in a given area.
This is especially true as global temperatures increase.
"Just a 10 percent slowdown in hurricane translational speed can double the increase in rainfall totals caused by 1 degree Celsius of global warming," says Kossin, a researcher at the National Oceanic and Atmospheric Administration's (NOAA) Center for Weather and Climate. He is based at the University of Wisconsin-Madison.
The study compared 68 years (1949-2016) of worldwide hurricane track and intensity data, known as best-track data, from NOAA to identify changes in translational speeds. It found that, worldwide, hurricane translational speeds have averaged a 10 percent slowdown in that time.
One recent storm highlights the potential consequences of this slowing trend. In 2017, Hurricane Harvey stalled over eastern Texas rather than dissipating over land, as hurricanes tend to do. It drenched Houston and nearby areas with as much as 50 inches of rain over several days, shattering historic records and leaving some areas under several feet of water.
How much hurricanes have slowed depends on where they occur, Kossin found. "There is regional variation in the slowdown rates when looking at the 10 percent global average across the same time frame," he says.
The most significant slowdown, 20 percent, occurred in the Western North Pacific Region, an area that includes Southeast Asia. Nearby, in the Australian Region, Kossin identified a reduction of 15 percent. In the North Atlantic Region, which includes the U.S., Kossin found a 6 percent slowdown in the speeds at which hurricanes move.