<p>In April 2024, South China experienced unprecedented rainfall causing widespread socioeconomic disruption. We show that this extreme rainfall arose from atmospheric anomalies driven by record-breaking sea surface temperature anomalies across the tropical Pacific, Indian Ocean, and North Atlantic. Observations reveal that the western North Pacific subtropical high reached its northernmost position since 1979, intensifying moisture transport into South China, while an enhanced Okhotsk High promoted cold-air intrusions, thereby amplifying South China rainfall. Climate model experiments demonstrate that the sea surface temperature anomalies across all three basins reinforced the anomalous anticyclone over the western North Pacific and enhanced Southeast Asian rainfall. Additionally, warming in the tropical Indian and Atlantic Oceans may enhance rainfall by intensifying the Okhotsk High. These results identify pan-tropical ocean warming as a key driver of the event and highlight the synergistic impacts of inter-basin interactions. Our findings underscore the growing importance of warm ocean basins in shaping regional hydroclimate extremes and provide insights to improve prediction and risk management in a warming climate.</p>