Landfalling tropical cyclone characteristics and their multi-timescale variability connected to monsoon and easterly formation environments over the western North Pacific

This study analyses the impacts of tropical cyclones (TCs) that formed in monsoon and easterly environments on the major coastlines of the western North Pacific (WNP) basin during 1981–2009. The TC formation processes, defined as the development of tropical cloud cluster to TC, associated with monsoon environments (monsoon trough, monsoon confluence, and north of monsoon trough) are categorized into monsoon-type TCs (monsoon-TCs). Similarly, those associated with easterly flow environments (easterly flow west and southwest of subtropical high) are categorized into easterly-type TCs (easterly-TCs). Monsoon-TCs form farther westward and at lower latitudes than easterly-TCs, contributing to higher landfall proportion on the coastal countries for monsoon-TCs. Monsoon-TCs have a higher probability of affecting southern China, Taiwan and Vietnam, while easterly-TCs tend to affect eastern China, southern Japan and the Philippines. Monsoon-TCs have more widely dispersed rainfall and slower translation speed during landfall than easterly-TCs. These characteristics are consistent with stronger environmental moisture transport and weaker steering flow in monsoon environments. Landfalling TC intensity and size are not different between easterly- and monsoon-TCs. Both easterly- and monsoon-TCs have interannual (1–4 years) and interdecadal (8–11 years) variability, which are related to variability of the large-scale monsoon trough. El Niño–Southern Oscillation is significantly correlated with the interannual variability of easterly- and monsoon-TCs, and changes in the monsoon-TC landfall proportion and easterly-TC landfall intensity. The interdecadal variability mainly affects the background vorticity and cyclonic circulation, leading to changes in the formation number of easterly- and monsoon-TCs. In summary, this study provides evidence for connections between multiscale variability of the large-scale monsoon and easterly patterns, TC formation environments, and TC impacts on the WNP coasts.