SAN JUAN Puerto Rico (Reuters) - Hurricane Gonzalo is expected to become a major hurricane on Tuesday as it moves over the open Atlantic waters and swirls away from the northern Caribbean islands, the U.S. National Hurricane Center said.

It said the center of Gonzalo, a Category 2 hurricane, was moving northwest, away from the British and U.S. Virgin Islands and Puerto Rico, prompting storm alerts for those areas to be lifted.

The islands of St. Martin and St. Barthelemy remained under tropical storm warnings, the Miami-based hurricane center said.

Most forecasts showed Gonzalo posing no threat to the mainland United States and moving still further north into the Atlantic.

Gonzalo was about 105 miles (170 km) north of St. Thomas in the U.S. Virgin Islands and packed sustained winds reaching 110 miles per hour (175 km per hour) early on Tuesday, the center said.

A major hurricane is considered to be Category 3 or above with winds hitting at least 111 mph (178 kph).

Dangerous rip currents from the storm's swells were likely to affect the Virgin Islands, the northern coast of Puerto Rico and parts of the Bahamas, forecasters said.

On Monday, Gonzalo's heavy rains and high winds destroyed several fishing boats, blew off roofs and downed power lines in Antigua and Barbuda.

Antiguan Prime Minister Gaston Browne ordered schools closed for a national cleanup effort on Tuesday to get the nation "fully back in business" by Wednesday.

Gonzalo is the sixth hurricane of the 2014 Atlantic hurricane season, which runs through the end of November. Forecasters in August predicted lower than usual activity for the season, with seven to 12 named storms and no more than two reaching major hurricane status.


(Reporting by Colleen Jenkins, David Adams, Curtis Skinner and Reuters in San Juan; Editing by Mohammad Zargham)