Hurricane Melissa strengthened to Category 4 with potential to reach Category 5, threatening Jamaica, Haiti and other Caribbean islands with catastrophic flooding and torrential rain.

The slow-moving Melissa strengthened into a major Category 3 hurricane late Saturday as it threatened catastrophic flooding in the northern Caribbean.

Areas of Jamaica could “already be experiencing tropical storm force winds & heavy rains,” with conditions expected to “get much worse there through Monday and Tuesday,” the NHC said.