During this early phase, two tropical cyclones dissipated and another became extratropical across the western Pacific basin; this caused the monsoon trough, which spawned most of the storms in the basin, to realign in a more climatologically appropriate manner.[2] According to the Japan Meteorological Agency (JMA), Omar developed into a tropical depression at 1800 UTC on August 23.[4] The Joint Typhoon Warning Center (JTWC) assessed a slower pace of strengthening, issuing a tropical cyclone formation alert at 2100 UTC before initiating advisories on Tropical Depression 15W on August 24.[2]