SAN JUAN, Puerto Rico (AP) — 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. While the compact hurricane’s center wasn’t expected to hit land, it threatened to dump flooding rains as it continued to grow larger.

Hurricane Erin is now a Category 4 storm, rapidly intensifying overnight into early Saturday morning as it moves closer to the U.S. East Coast with sustained winds up to 155 mph.

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.