The precursor disturbance to Typhoon Wanda was first observed on August 23 near Pohnpei in the Federated States of Micronesia. That day, a circulation formed in the interaction between the Mid-Pacific trough and an easterly wave, with energy from a surge in the Easterlies in the Southern Hemisphere. Initially winds were very weak, and it tracked west-northwestward while slowly gaining intensity. The official track from the Japan Meteorological Agency (JMA) indicated the system first developed into a tropical cyclone on August 25, whereas the Joint Typhoon Warning Center (JTWC) initiated advisories two days later, after it was observed by the Hurricane Hunters. It was designated Tropical Depression 59 while located about 1120 km (700 mi) northeast of the Philippines.