North Atlantic SSTA triggers persistent extreme precipitation over South China by modulating the 25–50-day intraseasonal oscillation

This study identifies the 25–50-day intraseasonal oscillation (ISO) as the dominant mode governing regional persistent extreme precipitation events (RPEPEs) over South China (SC) during rainy season (April–September) of 1979–2020. The primary external forcing for these events is the sea surface temperature anomalies (SSTA) in two distinct regions: the mid-to-high latitude (R1) and the subtropical (R2) North Atlantic. SSTA in R1 and R2 exhibit significant positive correlations with RPEPEs 25–17 days prior to their occurrence. Diagnostic analysis reveals that R1 SSTA warming excites localized diabatic heating, forcing upper-level divergence and inducing a Rossby wave source via vortex stretching. Concurrently, intensified R2 SSTA strengthens the meridional SST gradient over subtropical to mid-latitude North Atlantic, shifting the westerly jet northward. The resulting intraseasonal Rossby wave train originating from the mid-to-high latitude North Atlantic propagates southeastward along the enhanced westerly jet, intensifying vertical motion over SC to trigger RPEPEs. Linear baroclinic model experiments confirm that R1 SSTA primarily drives Rossby wave generation, whereas R2 SSTA enhances the meridional SST gradient, driving a northward shift and intensification of the westerly jet that favors Rossby wave propagation. This mechanistic linkage benefits improving the subseasonal forecasting skill of RPEPEs over SC. • The 25–50 day intraseasonal oscillation is the dominant mode for persistent extreme precipitation over South China. • Two crucial North Atlantic SSTA regions force the intraseasonal Rossby wave train: mid-to-high latitude warming excites the wave train, while subtropical warming strengthens the jet waveguide. • This dual-region mechanism provides a subseasonal predictive signal with a 25–17 day lead time.