MIAMI, (Reuters) – Hurricane Bill trekked  west-northwest over the open Atlantic yesterday and was poised  to develop into a major hurricane, but its forecast path seemed  likely to miss the U.S. East Coast.

The U.S. National Hurricane Center said that Bill, the     Atlantic season’s first hurricane, was packing top winds near  110 miles per hour (175 km per hour), just one mph short of  turning into a Category 3 hurricane.

“Bill is expected to become a a major hurricane tonight or  Wednesday,” the NHC said, saying its center was located at 1700  EDT (2100 GMT) about 635 miles (1,025 km) east of the Caribbean  Leeward Islands.

The hurricane center, which sent a plane to probe the  cyclone’s swirling cloud mass yesterday, forecast Bill could  strengthen to a Category 4 hurricane in the next 24 hours.

Category 3, 4 and 5 storms on the Saffir-Simpson intensity  scale are those likely to cause the most damage.

Bill posed no threat to the U.S. Gulf of Mexico  oil-producing area. Its curving path was expected to take it  just west of Bermuda, a mid-Atlantic British territory and  reinsurance capital, by Saturday.

Bermuda authorities warned residents to be prepared.

Hurricane expert Jeff Masters, founder of the Weather  Underground website, said he expected Bill to move between  Bermuda and the U.S. East Coast toward Canada’s Maritime  Provinces.