 The origin of Typhoon Matsa is traced to the formation of an area of convection about 185 km ( 115 mi ) east of Yap in late July . The convection gradually consolidated over a weak low @-@ level circulation , and at 0300 UTC on July 30 the system was first mentioned in the Joint Typhoon Warning Center ( JTWC ) Significant Tropical Weather Outlook . Located within an area of moderate wind shear , the system continued to slowly organize , and by 1200 UTC on July 30 it was sufficiently organized for the Japan Meteorological Agency ( JMA ) to classify it as a weak tropical depression while located about 65 km ( 40 mi ) east of Yap . Shortly thereafter , the JTWC followed suit by issuing a tropical cyclone formation alert . The depression tracked steadily westward , followed by a turn to the northwest on July 31 under the influence of a mid @-@ level ridge to its east . It continued to organize , and at 1200 UTC on July 31 it intensified into Tropical Storm Matsa ; the depression was unofficially classified a tropical storm six hours earlier by the JTWC . Additionally , the Philippine Atmospheric , Geophysical and Astronomical Services Administration ( PAGASA ) named the system Tropical Storm Gorio , due to its location within the administration 's area of responsibility . 
