Bermuda was on alert Friday as Hurricane Bill churned closer, sending dangerous ocean swells to Puerto Rico and the Dominican Republic. The US National Hurricane Center warned that 'significant coastal flooding' could affect Bermuda, where former president Bill Clinton and his wife Secretary of State Hillary Clinton are vacationing, the State Department said. Forecasters added that the Category Three storm could produce large swells along the US East Coast, including Massachusetts, where President Barack Obama and his family are heading for a summer beach vacation on Sunday. At 1200 GMT Friday, Bill's eye was 385 miles (620 kilometers) south of Bermuda, and 820 miles (1,320 kilometers) southeast of the US coastline at Cape Hatteras, North Carolina, the NHC said. The first hurricane of the Atlantic season, Bill was moving towards the northwest at nearly 17 miles (28 kilometers) per hour, and was forecast to gradually turn north roughly parallel to the US east coast. Projections show it passing within some 340 miles (545 kilometers) of Boston on Sunday morning before veering to the northeast up the Canadian coast. Bill was packing maximum sustained winds of around 115 miles (185 kilometers) per hour, with higher gusts. The National Hurricane Center said that while Bill 'has become a little less organized,' it could still strengthen over the next day, adding it was expected to gradually weaken from Saturday. The Saffir-Simpson scale rates a storm's severity on a scale of one to five, with a Category Three hurricane packing dangerous winds that can cause extensive damage to populated areas. Category Four is reserved for hurricanes with 'extremely dangerous winds' that are expected to create 'devastating damage.' Hurricane-force winds spun off from Bill extended up to 115 miles (185 kilometers) from the storm's eye. Bermuda, a British overseas territory with important finance and tourism industries, could expect 'significant coastal flooding' caused by 'large and dangerous breaking waves,' the NHC said. Large swells 'generated by this hurricane are affecting Puerto Rico, Hispaniola, the Bahamas and Bermuda' and should also 'begin affecting most of the US east coast and the Atlantic Maritimes of Canada during the next day or two,' the NHC said. 'These swells will likely cause extremely dangerous surf and life-threatening rip currents,' the statement read. Hispaniola, the second-largest Caribbean island after Cuba, compromises the Dominican Republic and Haiti. Bermuda issued its tropical storm alert and hurricane watch alert earlier Thursday in preparation of Bill's arrival. The Atlantic hurricane season began on June 1 and ends on November 30. Weather experts earlier this month reduced the number of projected hurricanes in the north Atlantic this season to four, two of them major hurricanes with winds above 111 miles (178 kilometers) per hour. Bill's progress follows one of the calmest starts to the hurricane season in a decade, which researchers from Colorado State University attributed to the development of an El Nino effect in the Pacific. 