<p>This study concerns the interannual relationship between the El Niño-Southern Oscillation (ENSO) and subsequent springtime western North Pacific sea-surface temperature (WNPSST) anomalies (WNPSSTAs), with preceding western North Pacific anticyclonic (WNPAC) anomalies serving as a critical atmospheric bridge. We unveil the mechanism underlying the interdecadal variation of this interannual relationship using long-term observational and reanalysis datasets. Results show a delayed response of the WNPSST in April to the preceding WNPAC in January, which is mainly due to ENSO’s indirect influence on following April WNPSSTAs by strengthening the preceding anomalous WNPAC in January. The relationship between ENSO amplitude and the following January WNPAC (and thus April WNPSST) displays prominent interdecadal variation, which is mainly modulated by the Atlantic Multidecadal Oscillation (AMO); that is, a higher (lower) correlation between ENSO amplitude and the following January WNPAC (April WNPSST) appears during the negative (positive) AMO phase. Further analysis suggests that during the negative AMO phase, a stronger El Niño induces a stronger Gill response and excites stronger Rossby waves to enhance and maintain the WNPAC via local air-sea interaction, wind-evaporation-SST feedback, and wind-moist enthalpy advection. The positive WNPSSTAs persist into the El Niño decaying spring due to the transport of warm water from low latitudes and net downward heat flux. In the wind-moist enthalpy advection mechanism for the maintenance of the WNPAC, the El Niño-induced meridional wind anomaly under different AMO phases plays a dominant role in the strength differences of meridional moist enthalpy advection, while meridional gradient of background specific humidity plays a secondary role.</p>