SAN JUAN, Puerto Rico — Hurricane Erin exploded in strength to a Category 5 storm in the Caribbean on Saturday, rapidly powering up from a tropical storm in a single day, the National Hurricane Center said.

Heavy rains were forecast to start late Friday in Antigua and Barbuda, the U.S. and British Virgin Islands and southern and eastern Puerto Rico.

While the hurricane’s center wasn’t expected to hit land, it threatened to dump flooding rains in the Caribbean.