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.

Hurricane Erin formed in the Atlantic Aug. 15 and rapidly strengthened to a catastrophic Category 5 storm with 160 mph winds on Saturday, Aug. 16, according to the latest advisory from the National Hurricane Center.