Hurricane Erin rapidly intensified into a Category 4 storm in the Caribbean, earlier than forecasters had predicted.

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.

Tropical Storm Watches are now active for a string of Caribbean islands, including Anguilla, Barbuda, St. Martin, St. Barthelemy, Saba, St. Eustatius, and Sint Maarten, signaling the possibility of tropical-storm conditions within the next 48 hours