The Modulating Role of Western North Pacific Tropical Cyclones in La Niña‐Positive IOD Coupling

Abstract Climate change exacerbates hydroclimatic extremes, yet predicting risks for vulnerable Indo‐Pacific populations remains limited by overlooked storm‐climate linkages. The Indian Ocean dipole (IOD) and El Niño‐Southern Oscillation (ENSO) govern regional droughts, floods, and heat waves. While IOD and ENSO typically synchronize (e.g., positive IOD with El Niño), several positive IODs (pIODs) occur independently or even cooccur with La Niña—events that defy conventional modes and trigger mismatches in forecasts. Current theories predominantly attribute this phase mismatch phenomenon to internal forcing within the Indian Ocean, lacking robust identification of external forcing mechanisms—a critical gap that undermines the reliability of predictive frameworks. Here, we show that active western North Pacific (WNP) tropical cyclones (TCs) induce maritime continent subsidence, triggering anomalous easterly winds and sea surface cooling in the eastern tropical Indian Ocean, thus generating independent pIODs. Our findings identify a critical external forcing mechanism for the ENSO‐IOD phase discrepancy, filling a pivotal knowledge gap in current theoretical frameworks. By quantifying TCs' role as synoptic‐scale triggers of interannual extremes, we provide a basis for disaster agencies to integrate real‐time TC activity into early warning systems.