The linkage between the spring subtropical Indian Ocean Dipole (SIOD) events and tropical cyclone genesis frequency over the western North Pacific (WNP) in the following summer is investigated in this study. It is found that their correlation is positive and statistically significant with a greater number of TCs genesis over the WNP in summer of a positive SIOD year. After removing the ENSO effects, diagnostic analysis reveals that under positive SIOD conditions the summertime WNP monsoon trough becomes intensified. Correspondingly, there are enhanced lower‐level vorticity, reduced vertical zonal wind shear, increased middle‐level relative humidity and vertical velocity over the WNP, conductive to generation of more TCs. Further examination indicates that the Mascarene high and Australian high are strengthened successively from spring to subsequent summer in a positive SIOD year, contributing to the maintenance of SIOD‐related SST dipole anomalies in southern Indian Ocean due to SST–wind–evaporation feedback mechanism. The resulting cyclonic anomaly is formed at lower troposphere over the WNP induced by the prominently enhanced cross‐equator airflows and the related Ekman upwelling. At upper troposphere, there tend to be remarkably WNP divergence anomalies of the interhemispheric vertical circulation forced by the summertime SST patterns closely associated with positive SIOD cases. By contrast, the monsoon trough is weakened and the dynamic and thermodynamic conditions are unfavourable for the WNP TC genesis in summer of a negative SIOD year, in agreement with a lower‐level anticyclonic anomaly and suppressed deep convection over the WNP forced by the SIOD‐related SST anomalies. (a) Normalized time series of the spring (March–May) SIOD index (black line) and the following summer (June–August) WNP TC genesis frequency index (grey shadings). (b) Correlation map of the spring SIOD index and simultaneous SST (contours: 0.2). Red E and blue L in (a) denote El Niño and La Niña years, respectively. Shadings in (b) indicate the regions significant passing 99% confidence level