Many of those 10 hurricanes have not hit the U.S. mainland — and Ophelia isn’t expected to reach America either. But a few others, including Harvey, Irma and Maria, have left dozens in the U.S. dead and caused billions of dollars in damage. Hurricane season continues through the end October, leaving the potential for even more destruction.
This year’s unusually strong storm season comes after years of relative hurricane drought. No major hurricane — a Category 3 storm or stronger with sustained winds of at least 111 mph — had made landfall in the U.S. since 2005.
Strong storm seasons come and go as a result of a variety of factors, including the presence of El Niño and other climate patterns. But scientists say that climate change is also making storms more severe, since warmer ocean water helps storms strengthen.
“A warmer ocean makes a warmer atmosphere,” Gabriel Vecchi, a professor of geosciences at Princeton University, told TIME earlier this year. “A warmer atmosphere can hold more water.”