Tropical storm Sandra formed in the Pacific Tuesday off Mexico with potential to reach hurricane strength before weakening as it approaches the coast, US forecasters said. The storm, which was packing sustained winds of 50 miles (85 kilometers) per hour, was located 550 miles (890 kilometers) southwest of Manzanillo, Mexico, the Miami-based National Hurricane Center said at 1500 GMT. "Strengthening is forecast during the next 48 hours, and Sandra is expected to become a hurricane on Wednesday," it said.