Abstract
The tropical western Pacific (TWP) has profound influences on climate. ENSO is an important source of interannual variability of TWP SST, but extratropical precursors are far less known. Here we show a significant interhemispheric influence from subtropical Southwest Pacific (SWP) on the TWP. Observational analysis suggests that SWP SST in boreal spring has strong coherence with TWP 6 months later. The spring SWP warming signal exhibits a unique interhemispheric propagation embedded in the southerly cross-equatorial flow over the western Pacific. The wind-evaporation-SST feedback initiates and maintains the progression of warm SST anomalies toward the TWP in autumn. The climate model successfully reproduces such an interhemispheric SST propagation. The seasonal evolution of SST variability improves the predictability of the warm pool SST by about 6 months. An SWP SST-based prediction model shows considerable hindcast skill (r = 0.80, p < 0.01), indicating that it is a valuable precursor of the TWP.