LES CAYES, Haiti—The death toll from a magnitude 7.2 earthquake in Haiti soared on Sunday as rescuers raced to find survivors amid the rubble ahead of a potential deluge from an approaching tropical storm. Saturday’s earthquake left at least 724 dead and 2,800 injured in the Caribbean island nation, with thousands more displaced from their destroyed or damaged homes. Survivors in some areas were forced to shelter in streets or soccer fields with their few salvaged belongings while overloaded hospitals scrambled to help those who were injured. Yet the devastation could soon worsen with the coming of Tropical Storm Grace, which was predicted to reach Haiti late Monday or early Tuesday, bringing the potential for torrential rain, flooding and landslides. The U.S. National Hurricane Center forecast 4 to 8 inches (10 to 20 centimeters) of rain in Haiti and the Dominican Republic, with up to 15 inches in some southern …