Tropical Storm Pilar formed in the Pacific, threatening to bring heavy rains to the southwestern coast of Mexico, the National Hurricane Center said Saturday.

Heavy rain is expected in the western portions of the Mexican states of Michoacan, Colima, western Jalisco and Nayarit through Monday, the National Hurricane Center said. Up to 15 inches of rain are possible in some areas, and the rainfall may cause life-threatening flash floods and mudslides.

Pilar had maximum sustained winds of 40 mph, and the winds could strengthen as it nears landfall.

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Mexico City is reeling from a 7.1-magnitude earthquake that hit earlier this week. The head of Mexico's Civil Defense Agency said Saturday the death toll from that disaster climbed to 307.

In August, Tropical Storm Lidia slammed the resort area of Los Cabos, north of where Pilar is expected to hit. The storm killed several people and 1,400 people sought refgue in Los Cabos' resorts.