Eric was 140 miles south of Acapulco, Mexico, and moving northwest at 12 miles per hour, the National Hurricane Center in Miami said in its 8 p.m. PDT advisory.
Maximum sustained winds were 45 mph with higher gusts, and some strengthening was forecast over the next two days.
A tropical storm warning was in effect from Lazaro Cardenas to Manzanillo, while a tropical storm watch was in effect from Acapulco to east of Lazaro Cardenas and for West of Manzanillo to La Fortuna.
Erick was expected to turn to the west-northwest by late Friday or Saturday, moving parallel to but offshore of Mexico's southwest coast.
Tropical-storm-force winds extended 45 miles from the center, and gusty winds with rain bands were reported near the southern coast of Mexico.
Three to 5 inches of rain was expected with localized amounts of as much as 8 inches, with the potential for life-threatening flash floods and mudslides.
Meanwhile, Depression Dalila weakened as it moved away in the Pacific Ocean and was expected to degenerate into a remnant low Friday.