MIAMI (AP) - U.S. forecasters say Tropical Storm Sonia has formed in the Pacific off the southern tip of Mexico's Baja California peninsula. The U.S. National Hurricane Center in Miami said Sonia grew from a tropical depression and was centered Sunday about 285 miles (455 kms) south of the southernmost tip of the peninsula. Maximum sustained winds stand at 40 mph (65 kph) and the storm is moving north at 7 mph (11 kph). The center says a tropical storm warning extends from Mazatlan northward to Altata along northwest Mexico's mainland. Forecasters expect Sonia to pass south of the Baja California peninsula in coming hours and approach the mainland coast early Monday. Forecasters say Sonia is expected to dump heavy rains in a wide area and could produce life-threatening flash floods and mudslides.