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.

热带西太平洋（TWP）对气候有着深远的影响。ENSO 是 TWP SST 年际变率的一个重要来源，但温带前兆却鲜为人知。在这里，我们展示了副热带西南太平洋 (SWP) 对 TWP 的显着半球间影响。观测分析表明，北方春季的 SWP SST 与 6 个月后的 TWP 有很强的相干性。春季 SWP 变暖信号表现出一种独特的半球间传播，嵌入在西太平洋上空的向南横穿赤道流中。风-蒸发-SST 反馈启动并维持了秋季暖SST 异常向TWP 的进展。气候模型成功地再现了这种半球间 SST 传播。SST 变率的季节性演变将暖池 SST 的可预测性提高了约 6 个月。基于 SWP SST 的预测模型显示出相当大的后预测技巧（r  = 0.80, p  < 0.01)，表明它是 TWP 的有价值的前体。