The interannual variability of boreal summer Asian-Australian monsoon (BSAAM) is mainly driven by sea surface temperature anomalies (SSTAs) in the Indian, Pacific, and Atlantic Oceans. Unlike traditional studies that examine the influence of individual oceans on BSAAM subsystems, this study elucidates the distinct and combined impacts of all three oceans on the BSAAM as a unified system. First, we quantify the contributions of the three oceans to the dominant interannual variability of BSAAM using Community Earth System Model (CESM) pacemaker experiments, showing that Pacific, Atlantic, and Indian Oceans contribute approximately 46%, 35%, and 23%, respectively. These quantified contributions capture both the simultaneous influences of the oceans and their effects from preceding seasons. During boreal summer, BSAAM-related SSTAs in the Indian Ocean-Western Pacific (IOWP), the Central-Eastern Pacific (CEP), and the Tropical Atlantic (TA) create a tripole pattern across the tropics. Both the IOWP and CEP directly influence the BSAAM, with the IOWP having a slightly stronger effect. In contrast, the TA’s influence is indirect and relatively weaker, mediated through its interactions with the IOWP and CEP. Differently, from the preceding boreal winter to boreal summer, the TA emerges as the most significant factor, showing progressively strengthening positive SSTAs, similar to the IOWP, while the CEP transitions from an El Niño phase to a La Niña phase. Compared to predictions based on individual oceans, combining the influences of all three oceans extends the BSAAM prediction lead time into the preceding winter and nearly doubles the average precipitation prediction skill in the BSAAM region. These findings provide new insights into forecasting the BSAAM from a comprehensive, multi-ocean perspective.

Asian-Australian monsoon,Three oceans,Prediction skill