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.

As of Friday evening, Hurricane Erin had strengthened into a Category 2 storm with maximum sustained winds of up to 100 mph and "expected to rapidly intensify into a major hurricane this weekend," the National Hurricane Center said at 11 p.m. ET.

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.