Cosme was about 320 miles southwest of Manzanillo, Mexico, and about 500 miles south-southeast of Cabo San Lucas, with maximum sustained winds of 65 miles per hour, the National Hurricane Center in Miami said.
No coastal watches or warnings were in effect, though the storm was expected to begin affecting portions of Mexico's Pacific coast Tuesday, generating dangerous surf and rip current conditions.
Cosme was moving northwest at 14 mph, the hurricane center said in its 8 p.m. PDT Monday advisory, and was expected to turn west-northwest Tuesday through Wednesday.
Tropical-storm-force winds extended 175 miles from the center, and Cosme was expected to strengthen to hurricane status Tuesday.
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