Hurricane Erin, after strengthening into a Category 5 storm early Saturday, weakened to Category 3 by Sunday morning and has taken a track slightly more south than originally forecast, the National Hurricane Center said.

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 reached Category 5 status before weakening but has brought significant rain to the Virgin Islands and Puerto Rico.

Despite this, the US National Hurricane Center (NHC) says Erin is growing in size, with tropical-storm-strength winds extending 205 miles from its centre. Storm-related hazards, including flash flooding and landslides, are expected in the Virgin Islands and Puerto Rico.

An eyewall replacement cycle is underway within Hurricane Erin as the monster storm continues to barrel across the Atlantic while bringing gusty winds and rain to Puerto Rico and the Virgin Islands after rapidly intensifying into a catastrophic Category 5 hurricane over the weekend.

Erin is the first hurricane to develop over the Atlantic this year, and meteorologists are closely tracking its path and forecast.

Erin, the first hurricane of the season, is now forecast to become a Category 4 by Sunday. Here's where it could head in the week ahead.

Officials in the northern Caribbean are warning of heavy rains and dangerous swells as Tropical Storm Erin approaches the region.