Dalila's origin is a tropical wave that moved westward from Africa and over the eastern tropical Atlantic Ocean on July 10. It crossed northern South America and Central America on the July 15 through July 17 accompanied by vigorous thunderstorm activity, and then entered the Pacific basin on July 18 as an organized area of disturbed weather. Early on July 21, the system acquired a low-level circulation and became Tropical Depression Five-E, about south of the Gulf of Tehuantepec. Moving west-northwestward, it became Tropical Storm Dalila with winds 12 hours later.