Hurricane Idalia’s arrival on Florida’s Gulf Coast on Wednesday signaled activity in the Atlantic’s hurricane alley might not be as quiet this year as meteorologists had once predicted.

Scientists initially forecast in May that the U.S. would see a near-normal Atlantic hurricane season, but raised that forecast in mid-August, projecting a more dangerous storm season.

That is because worldwide surface ocean temperatures have been exceedingly warm this year, with temperatures in and around the Florida Keys mirroring a hot tub this summer.