The idea of a slow-moving storm isn’t exactly a new one. Hurricane Harvey in 2017 bore a similar signature. A recent study showed that the speed of tropical cyclones worldwide over land has decreased by ten percent in the last 70 years, between 1949 and 2016. The science isn’t settled on the cause of the slowdowns, but, if these trends continue, hurricanes like Harvey and Florence -- and the devastating flooding they caused -- could become increasingly common.