Rapid intensification (RI) of tropical cyclones (TCs) near the China coast poses heightened risk because short lead times limit preparedness. Using ERA-Interim reanalysis, Tropical Rainfall Measuring Mission precipitation, and TC best-track data, we apply an obliquely rotated T-mode principal component analysis to classify synoptic environments for RI events and diagnose controlling factors with composites and a Box Difference Index. Four synoptic flow patterns emerge: (1) MSS: combined monsoon trough, subtropical high, and South Asian high; (2) MS: monsoon trough interacting with the subtropical high; (3) SH: subtropical-high-dominated; and (4) MW: monsoon trough with a southward-penetrating midlatitude westerly trough. Across regimes, RI is preceded by radius-of-maximum-wind contraction, increased TC fullness, and more axisymmetric inner-core precipitation. Further analyses show that MSS/MS feature reduced vertical wind shear and stronger low-level vorticity with enhanced precipitation; SH shows the weakest shear and strongest upper-level divergence as the ridge extends westward; MW favors already compact, intense storms that can withstand shear asymmetry tied to the midlatitude westerly trough. These results clarify how large-scale flow modulates RI onset near the China coast and suggest that combining synoptic-pattern recognition with environmental predictors can improve RI guidance for coastal warnings.

Rapid Intensification, Synoptic Patterns, China coast, Monsoon Trough, Vortex Axisymmetrization