熱帶氣旋形成警報
A low-pressure area formed east of Palau on September 9 and gradually drifted westward. Early on September 10, the Japan Meteorological Agency (JMA) upgraded it to a tropical depression, before the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert on the system later that day and also upgraded it to a tropical depression late on the same day, as Sanba started to become more organized, with the banding of thunderstorms strengthened, and wrapped more tightly into the low level circulation center .