<p>Understanding the variability in the commencement and termination of the tropical Asian summer monsoon (TASM) is critical for effective water resource management and agricultural planning. This study employs multivariate empirical orthogonal function to objectively define large-scale monsoon commencement and termination, thereby quantifying the duration of the TASM. The analysis reveals that monsoon duration is significantly influenced by the preceding wintertime Victoria Mode, which is the second leading mode of sea surface temperature (SST) variability in the North Pacific. Specifically, during positive phase of the Victoria Mode, cold SST anomalies dominate the subtropical North Pacific, flanked by warm anomalies to the north and south. This SST pattern induces anomalous westerly winds over the tropical western Pacific, which can trigger El Niño development via oceanic-atmospheric positive feedbacks. The SST anomalies associated with the Victoria Mode and developing El Niño further induce large-scale divergent circulation, resulting in anomalous subsidence over the South China Sea and adjacent regions. The subsequent reduction in rainfall acts as a diabatic cooling source, exciting an equatorial Rossby wave response to the west. This response induces anomalous anticyclonic circulation and easterly winds over tropical Asia, thereby delaying the monsoon commencement and advancing its termination. As a result, the positive phase of the Victoria Mode shortens the monsoon duration and reduces the monsoonal rainfall. This study thus identifies a novel mechanism linking the Victoria Mode to TASM variability: rather than influencing peak summer rainfall directly, the Victoria Mode may exert its influence by altering monsoon duration.</p>