The 2003 Pacific typhoon season was a slightly below average yearlong period of tropical cyclogenesis exhibiting the development of 31 tropical depressions , of which 21 became named storms ; of those , 14 became typhoons . Though every month with the exception of February and March featured tropical activity , most storms developed from May through October . During the season , tropical cyclones affected the Philippines , Japan , China , the Korean Peninsula , Indochina , and various islands in the western Pacific .