SAN JUAN, Puerto Rico — Erin strengthened into a hurricane on Friday as it approached the northeast Caribbean, prompting forecasters to warn of possible flooding and landslides.

The storm is expected to remain over open waters, although tropical storm watches were issued for Anguilla and Barbuda, St. Martin and St. Barts, Saba, St. Eustatius and St. Maarten.

The hurricane center noted “there is still uncertainty about what impacts Erin may bring to portions of the Bahamas, the east coast of the United States, and Bermuda in the long range.”

Dangerous surf and rip currents are expected to affect the East Coast next week, with waves reaching up to 15 feet along parts of the North Carolina coast that could cause beach erosion, according to Accuweather.

“Erin is forecast to explode into a powerful Category 4 hurricane as it moves across very warm waters in the open Atlantic. Water temperatures at the surface and hundreds of feet deep are several degrees higher than the historical average,” said Alex DaSilva, Accuweather’s lead hurricane expert.

For Marylanders, Ocean City beach officials say conditions are becoming rough along the coast and will intensify over the next few days.

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. Up to 4 inches are expected, with isolated totals of up to 6 inches, according to the National Hurricane Center in Miami.

Forecasters also warned of dangerous swells.

The storm was located about 460 miles east of the Northern Leeward Islands. It had maximum sustained winds of 75 mph and was moving west-northwest at 18 mph.

Hurricane specialist and storm surge expert Michael Lowry said Erin is forecast to eventually take a sharp turn northeast that would put it on a path between the U.S. and Bermuda.

“The forecasts for next week still keep the future hurricane safely east of the mainland U.S.,” he said.

Erin, which is the Atlantic season’s first hurricane, is forecast to become a major Category 3 storm late this weekend.

Erin is the fifth named storm of the Atlantic hurricane season, which runs from June 1 to Nov. 30.

This year’s season is once again expected to be unusually busy. The forecast calls for six to 10 hurricanes, with three to five reaching major status with winds of more than 110 mph.