MIAMI - Forecasters issued a tropical storm warning for the Massachusetts coastline Saturday as Hurricane Bill sped toward the U.S. The warning, which includes the islands of Nantucket and Martha's Vineyard, means tropical storm-force winds of 40 mph or more could hit the coastline in the next 24 hours. President Barack Obama and his family plan to travel to Martha's Vineyard on Sunday for vacation.Meanwhile, a hurricane watch was discontinued for the island of Bermuda, though a tropical storm warning was still in effect.