Thunderstorm activity in the system, located 450 kilometers southeast of Acapulco, Mexico, became more intense and organized overnight on Saturday.
By Sunday morning, the system had developed into a tropical depression. Current models show the depression could reach hurricane intensity within 48 hours.
A hurricane watch and tropical storm warning are both in place for parts of Mexico's Pacific coast. Rainfall amounts of up to 200 mm are expected, with isolated higher totals possible in some mountainous areas.
The first hurricane of the eastern Pacific season, Adrian, fizzled out uneventfully last week.