The West Pacific Warm Pool (WPWP) plays a central role in modulating tropical convection, atmospheric circulation, and global climate variability, yet the long-term trends in its spatial extent and centroid displacement remain debated, particularly regarding the influence of decadal-scale Pacific and Atlantic modes. Here we analyze Optimum Interpolation Sea Surface Temperature (OISST) data from 1982 to 2025 to revisit WPWP evolution, focusing on surface area changes and centroid migration. Our results reveal a robust and accelerating expansion of the WPWP over the four-decade period, with the warm pool’s eastern and poleward boundaries advancing significantly. Contrary to some earlier findings of eastward heat-center shifts, we detect a net westward displacement of the centroid by approximately 1.8° longitude from 1982 to 2025, accompanied by a distinct poleward migration of ~0.9° latitude in both hemispheres, indicating asymmetrical subtropical encroachment. The expansion rate is strongly modulated by the Pacific Decadal Oscillation (PDO): positive PDO phases coincide with accelerated areal growth and enhanced westward extension, while negative phases temper expansion but do not reverse the long-term trend. Our findings reconcile previous conflicting reports on WPWP displacement. Collectively, this study underscores that WPWP expansion is not merely isotropic but involves a systematic westward and poleward reconfiguration, driven by the interplay of forced global warming and internal multidecadal variability. These results have critical implications for projections of tropical cyclone tracks, monsoon rainfall, and equatorial circulation dynamics under continued greenhouse forcing.