(Updates with Marty becoming a hurricane, details on rain impact)
MEXICO CITY, Sept 28 (Reuters) - Hurricane Marty formed on Monday, rolling northeast toward Mexico's Pacific Coast and threatening to dump heavy rain on the southwest of the country, the U.S. National Hurricane Center (NHC) said.
The hurricane, which is around 145 miles (233 km) west of the beach resort of Acapulco, was heading northeast at about 6 miles per hour (10 kilometers per hour) and producing maximum sustained winds of 80 mph (129 kph), the Miami-based NHC said.
Marty is likely to be near but just off the southwestern coast from Tuesday through Wednesday, the center said.
A hurricane warning was in effect from Tecpan de Galeana, in the southwestern state of Guerrero, north to the industrial port of Lazaro Cardenas, the NHC said.
Marty is likely to produce between 6 and 12 inches (15 to 30 cm) of rain in Guerrero, and could dump more in some areas, the center said. Lesser amounts of rain are likely to hit the neighboring state of Michoacan to the northwest, it added.
Mexican state oil company Pemex has no major installations close to the hurricane's expected trajectory.
Marty is likely to begin weakening on Tuesday but should be close to hurricane strength while nearing the coast, the NHC said. (Reporting by Joanna Zuckerman Bernstein; Editing by Dave Graham and Jonathan Oatis)