Tropical Storm Dianmu was a weak tropical cyclone that caused considerable damage over parts of Mainland Southeast Asia during late-September 2021. The fifteenth named storm of the 2021 Pacific typhoon season, Dianmu originated from an area of low-pressure situated in the South China Sea on September 21. Being first monitored by the Joint Typhoon Warning Center, the system rapidly consolidated to a tropical depression on September 22 as it continued to approach Vietnam before strengthening further to a weak tropical storm, with the Japan Meteorological Agency naming it as "Dianmu". Little intensification occurred before it made landfall on the country with winds of 35 knots (65 km/h; 40 mph). It then rapidly weakened over land and dissipated on September 24 as a tropical cyclone.