Tropical Cyclone Activity Over the Western North Pacific in 2013

This paper presents a review of tropical cyclone (TC) activity over the western North Pacific in 2013 and examines the main factors that influenced the pattern of activity. The 2013 season was characterized by an above-normal genesis number of named storms, near-normal total occurrence frequency, and near-normal accumulated cyclone energy. Both the tropical SSTs in the Pacific sector and the East Asian summer monsoon contributed to favorable conditions for active cyclogenesis. The monsoon circulation also controlled the TC track patterns. Three prevailing tracks were identified, along with four stages of track pattern transition that were characterized by different combinations of prevailing tracks. The different track patterns were associated with variations in the regional circulation, which in turn were closely related to the seasonal variation of the monsoon. The regional circulation was also influenced by the intra-seasonal oscillation. In particular, the quasi-biweekly oscillation (QBWO) was important during the early and late seasons, while the 30-60 day oscillation was significant in the active season from late July to early October. The QBWO mainly influenced the circulation in the subtropics and the midlatitudes, while the 30-60 day oscillation was related to the Pacific-Japan pattern, variation in the subtropical high, and tropical cyclonic circulation during the early, main, and late seasons, respectively.