MEXICO CITY (Reuters) - Tropical storm Ingrid strengthened to a Category 1 hurricane off Mexico's Gulf Coast on Saturday, becoming the second hurricane of the Atlantic season as it dumped heavy rain across eastern Mexico. Rain from the storm has caused river levels to rise and emergency services to prepare for evacuations, but state oil monopoly Pemex said its installations in the Gulf of Mexico were operating normally. Ingrid, with winds of 75 miles per hour, could grow even stronger over the next two days as it nears Mexico's coast, the U.S. National Hurricane Center (NHC) said. ...