 Typhoon Thad originated from an active monsoon trough several hundred miles east of the Philippines in mid @-@ August 1981 . On August 10 , a weak surface circulation was first noted on satellite imagery . At that time , the center was embedded within the monsoon trough . Within five days , the system developed outflow . Midday on August 15 , the Japan Meteorological Agency ( JMA ) first classified the system . Based on data from Hurricane Hunters , a Tropical Cyclone Formation Alert was issued by the Joint Typhoon Warning Center ( JTWC ) at 1800 UTC on August 15 . Situated south of a subtropical ridge , the cyclone was located within a favorable environment for further development . Early on August 16 , the JMA upgraded the system into a tropical storm . Following an increase in organization , the JTWC upgraded the system into Tropical Depression 15 that day . 
