Tropical Storm Richard weakened to a tropical depression on Monday as it moved across southern Mexico and headed for the Bay of Campeche, but did not look to pose a major threat to Mexican or U.S. oil operations. The storm is expected on Tuesday to pass near the platforms that produce the bulk of Mexico’s 2.6 million barrels per day of crude oil, but state oil monopoly Pemex said it was only taking the usual precautions and all operations were normal.