Exploring synoptic patterns contributing to extreme rainfall from landfalling tropical cyclones in China

Extreme rainfall resulted from landfalling tropical cyclones (ERLTC) can lead to severe disasters and enormous economic losses across China, highlighting the critical need to improve ERLTC forecasting accuracy for disaster prevention and mitigation. This study examines 789 ERLTC days in China from 1979 to 2019. These ERLTC days are classified into four dominant synoptic patterns (P1 to P4) using the self-organizing map method based on the configurations of landfalling tropical cyclones (TCs), the western Pacific subtropical high (WPSH), and associated low-level water vapor transport. These four patterns are characterized as follows: P1 (33.0 %) reflects a typical mid-summer circulation with WPSH and south Asian high (SAH) ridge lines around 25°N; P2 (30.0 %) exhibits a northward-shifted WPSH and SAH with double TC circulations; P3 (20.3 %) features a southward-shifted WPSH and SAH with the weakest TC and monsoon circulation; P4 (16.7 %) shows an eastward-shifted WPSH and SAH with the strongest TC circulation. Compared to P1, TCs are positioned further north in P2, further south in P3, and further east in P4. The intensity centers of ERLTC correspond closely with regions of column-integrated water vapor flux convergence and high-level divergence, located in southern coast areas under P1 and P3, southeast mainland and around Bohai Bay under P2, and along eastern coastal areas under P4. Meanwhile, ERLTC is confined to regions south of 30°N in P3 due to weaker water vapor transport. These findings offer valuable insights to comprehensively understand ERLTC events in China.