Bayesian analysis is applied to detect changepoints in the time series of seasonal typhoon counts in the vicinity of Taiwan. An abrupt shift in the typhoon count series occurs in 2000. On average, 3.3 typhoons per year have been noted before 2000 (1970-99), with the rate increasing to 5.7 typhoons per year since 2000 (2000-06). This abrupt change is consistent with a northward shift of the typhoon track over the western North Pacific-East Asian region and an increase of typhoon frequency over the Taiwan-East China Sea region. The northward shift of the typhoon track tends to be associated with typhoon-enhancing environmental conditions over the western North Pacific, namely, the weakening of the western North Pacific subtropical high, the strengthening of the Asian summer monsoon trough, and the enhanced positive vorticity anomalies in the lower troposphere. Based on observational analysis and model simulations, warm sea surface temperature anomalies over the equatorial western and central Pacific appear to be a major factor contributing to a northward-shifted typhoon track.
