Bill weakened to a Category 2 storm over the Atlantic as it nears Bermuda on track to pass between the island and the U.S. East Coast. Bill's maximum sustained winds had decreased to 110 mph.
Bill was expected to cause significant flooding along the Bermuda coastlines Friday and Saturday and Bermuda issued a tropical storm warning.
Along the eastern U.S. coast, waves of 20 feet and more offshore and rip currents at the beach are expected over one of the summer's last weekends. Swimming has been banned at beaches along much of the East coast. Across the eastern seaboard are warnings of rip currents, which kill nearly 100 swimmers every year and force more than 20 thousand rescues, reports CBS News correspondent Kelly Wallace.
A hurricane generates powerful waves that help form rip currents, which are narrow, fast-moving channels of water that flow away from the shore and pull swimmers out to sea. They usually develop at low spots, like sand bars.
Swimmers caught in rip currents should swim parallel to the shore, out of the narrow current. Swimming toward land is a losing battle.
Bill is a massive storm right now - some 500 miles across, reports Early Show weather anchor Dave Price.
The National Weather Service said seas will get increasingly dangerous on Saturday into Sunday. Waves of up to 20 feet are possible south of Martha's Vineyard and Block Island and east of Cape Cod, and up to 35 feet on portions of the prime fishing area of Georges Bank, the weather service said.
President Barack Obama and his family plan to travel to Martha's Vineyard off the Massachusetts coast on Sunday for a vacation.
Mariners from Rhode Island up to Maine were told to stay close to port because of the high seas and what could be tropical storm-force winds. Steve Kass of the Rhode Island Emergency Management Agency said anybody offshore south of New England will face "absolutely dangerous conditions."
Bermuda's storm warning means winds of 40 mph or more were expected to arrive within a day, and the island remained under a hurricane watch that indicated even stronger winds were possible within 36 hours.
Thursday's warning came a day after former U.S. President Bill Clinton and his wife, Secretary of State Hillary Rodham Clinton, arrived in Bermuda on Wednesday for a 3- or 4-day getaway.
The government urged islanders to secure boats and finish other storm preparations. Officials put up warning signs at beaches along the south shore because of large swells and rip currents ahead of the storm.
The storm's center is expected to pass between Bermuda and the U.S. eastern coast on Saturday. Forecasters said large swells from the storm were affecting Puerto Rico, Hispaniola, The Bahamas and Bermuda.
The center's five-day track showed Bill staying well out to sea off the U.S. coast and inching closer to land off Canada's Maritime provinces before veering back out into the North Atlantic.
Just before 2 p.m. Eastern, Bill was centered about 290 miles south-southwest of Bermuda and about 695 miles southeast of Cape Hatteras, N.C. The hurricane is moving northwest near 18 mph.
Bill is the first Atlantic hurricane this year after a quiet start to the season that runs from June through November. The Miami center lowered its Atlantic hurricane outlook on Aug. 6 after no named tropical storms developed in the first two months.
The revised prediction was for three to six hurricanes, with one or two becoming major storms with winds over 110 mph. Researchers at Colorado State University have also lowered their Atlantic season forecast to four hurricanes, two of them major.