MIAMI : Hurricane Arthur gained strength as it churned off the US East Coast on Thursday, with drenching rains and gusting winds that promise to disrupt the July 4 holiday for millions of Americans.At 1200 GMT, Arthur was 150 miles (240 kilometers) southwest of Cape Fear, North Carolina, packing maximum sustained winds of 80 miles (130 kilometers) per hour, the National Hurricane Center said. The Miami-based weather center said Arthur is expected to approach the Outer Banks resort region of North Carolina late Thursday, laying waste to many Americans’ vacation plans for the Independence Day holiday.News reports said that in the coastal Carolinas alone, as many as half a million visitors had been expected for the national holiday, the region’s biggest tourist weekend.Dangerous storm swells were expected as far south as central Florida, and fireworks displays and holiday parades were being rescheduled on Thursday as far north as New England. Arthur was moving northward at nine miles (15 kilometers) per hour and was expected to pick up speed. A storm surge of up to four feet (1.2 meters) was possible in North Carolina’s Outer Banks. Through Friday, rainfall of up to six inches was expected in coastal areas of North Carolina.The storm is the first of the Atlantic hurricane season, which started on June 1 and runs through November 30.