Hurricane Erin has strengthened into a Category 2 storm as it approaches Puerto Rico and the Virgin Islands, bringing heavy rains that could cause flooding and landslides.

Hurricane Erin forced tourists to cut their vacations short on North Carolina’s Outer Banks even though the monster storm is expected to stay offshore after lashing part of the Caribbean with rain and wind on Monday.

Tracking Hurricane Erin, the first named storm of the Atlantic hurricane season, which weakened to a Category 3 storm early Sunday.

Storms that ramp up so quickly complicate forecasting and make it harder for government agencies to plan for emergencies. Hurricane Erick, a Pacific storm that made landfall June 19 in Oaxaca, Mexico, also strengthened rapidly, doubling in intensity in less than a day.

Forecasts nudge Erin's likely path to the west, increasing the risks at U.S. beaches. Tropical storm conditions are expected in North Carolina's Outer Banks starting late Wednesday.