Historically, the climatological mean northward flow in the Yellow Sea trough has been referred to as the Yellow Sea Warm Current (YSWC) since it was thought to originate as a branch of the Tsushima Current which transports warm Kuroshio waters. However, the Tsushima Current does not penetrate into the Yellow Sea interior during winter. The onset of what is referred to as the YSWC during winter is directly observed using measurements of current profiles, pressure, and temperature, and a wind climatology for the time period July 1995 through January 1996. The YSWC is a result of weak southerly winds during summer. During full transition and winter monsoon periods, strong northerly wind bursts drive a north-to-south rise in pressure extending from the trough over to the Korean coast and force a northward flow in the Yellow Sea trough. The rise in pressure and corresponding north wind-forced YSWC begin at the end of October for this measurement period and are observed into January. These measurements show that the YSWC has different seasonal forcing mechanisms. Direct current measurements are also presented which suggest a current flow north of Cheju, sometimes referred to as the Cheju Warm Current. ¿ 2000 American Geophysical Union