Tropical Storm Andres was the first of many storms of the season, with above-average activity due to one of the strongest El Niño events on record. In most of May 1997, strong westerlies extended across the eastern Pacific Ocean, which inhibited tropical cyclogenesis. Toward the end of the month, however, wind shear decreased in the easternmost portion of the basin, which allowed a low-level circulation to develop; it is possible the system originated from a tropical wave that traversed the Atlantic Ocean in the previous two weeks. Deep convection increased over the circulation on May 31, prompting classifications with the Dvorak technique. Based on satellite imagery, it is estimated the system developed into Tropical Depression One-E early on June 1, about south of the Gulf of Tehuantepec.
