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.

Erin, the first hurricane of the season, is now a powerful Category 4 hurricane. Here's where it could head in the week ahead.

Erin has strengthened into a hurricane as it approaches Puerto Rico and the Virgin Islands, bringing heavy rains that could cause flooding and landslides.

Hurricane Erin, now a Category 5 storm, with maximum sustained winds of 160-mph, is expected to continue strengthening.

Heavy rains are forecast to start with the storm expected to become a major Category 3 storm over the weekend.

Hurricane Erin was expected to soak the Virgin Islands and Puerto Rico with heavy rain through the weekend before heading north up the Atlantic.

However, the severity of those impacts is unknown at this time. Swells generated by Erin will begin affecting portions of the northern Leeward Islands, the Virgin Islands and Puerto Rico by this weekend. These swells are likely to cause life-threatening surf and rip current conditions, the NHC said.