Does Tropical Cyclone Formation over the Western North Pacific Have Poleward Shifts Due to Anthropogenic Forcing?

Recent studies show that the annual basin-wide mean location of tropical cyclone (TC) formation exhibits a northward shift in the western North Pacific (WNP) basin over the past three decades, which is consistent with the northward migration of annual mean latitudes of the TC lifetime maximum intensity (LMI). It is unclear whether the shift was related to the anthropogenic influence on TC activities. In this study, the role of interdecadal variations on TC formation locations over the past 58 years is examined. It is found that there are two interdecadal modes of the monsoon trough (MT), which are associated with the Pacific decadal oscillation (PDO) and the interdecadal Pacific oscillation (IPO), respectively. The interdecadal variations of the MT play an important role in the northward migration of TC formation. It is demonstrated that the observed poleward shift of TC formation over the WNP is mainly attributed to the natural variability in the past three decades with no significant poleward shift of TC formation over the past six decades.