Tropical Cyclone Motion in the Western North Pacific under the Global Warming Trend: Exploring Moderated Changes and the Interplay of Synoptic-Scale Systems, Large-Scale Circulations, and SST Warming Patterns

Tropical cyclone (TC) motion critically influences the geographical extent of TC impacts. Furthermore, it has a consequential effect on the severity of TC impacts by modulating TC intensity, structure and rainfall. The motion of TCs dictates the environments they traverse, thereby influencing their evolution. In the existing literatures, the impact of global warming on TC translation speed (TCTS) presents mixed signals and varying opinions. Studies have shown that the change in the geographic distribution of TC positions (e.g., TC frequency by latitudes) and TC’s steering flow collectively influences the mean TCTS. Additionally, analysis of historical observational data suggests that multi-decadal variability can contribute to altering the mean TCTS.

In this study, TC motion in the western North Pacific is assessed through the track-cluster analysis of one retrospective simulation and four ensemble future projections (late 21^st century) under the RCP 8.5 scenario from the High-Resolution Atmospheric Model at 25-km resolution. The future runs are forced by four different SST warming patterns based on the CMIP5 results. The experimental design ensures that identified changes are solely attributed to the global warming trend, excluding the influence of varying interannual variabilities under global warming. The track-clustering approach facilitates a detailed examination of TC behaviors by the regions of impact and the environments that TCs are interacting with, and reduces the impact of TC position shifts on TCTS changes through intra-cluster examinations.

Results from six distinct clusters, stratified by TC genesis zones and moving patterns, reveal a trend towards faster intra-cluster mean TCTS in a warmer future. However, statistical significance is limited, with only a subset of outcomes reporting a meaningful increase (0.4 – 0.75 m s^-1). The presentation will delve into the underlying physical causes behind this identified trend. By exploring the intricate interplay of synoptic-scale systems (e.g., monsoon trough, subtropical high, westerly jet), large-scale circulations (e.g., Hadley and Walker cells), and SST warming patterns, the presentation aims to shed light on the complex dynamics shaping TC behaviors in the western North Pacific under global warming.