Ocean Forcing and Climate Warming Driving the 2025 Record-Breaking Humid Heatwave in Central–Eastern China

During midsummer 2025, central–eastern China (CEC) experienced an unprecedented humid heatwave that ranked first in both intensity and spatial extent, and third in duration since 1961. This study investigates the dynamical drivers and thermodynamic forcings responsible for this extreme event. Dynamically, the heatwave was sustained by a persistent anomalous high-pressure system over CEC. This feature resulted from a pronounced northwestward extension of the western North Pacific subtropical high (WNPSH) and an eastward-propagating Rossby wave train along the Eurasian subtropical jet. These circulation anomalies induced strong subsidence and clear-sky shortwave radiative heating. Concurrently, anomalous southeasterly flow along the western flank of the WNPSH transported abundant moisture from the Pacific Ocean into CEC. The anomalous circulation features were further linked to strong warm sea surface temperature (SST) anomalies over the northwestern Pacific and mild warming in the western equatorial Pacific, which together accounted for approximately half of the observed wet-bulb temperature anomaly over CEC. Furthermore, long-term climate warming contributed roughly 40% to the magnitude of this wet-bulb temperature anomaly, substantially amplifying its extremeness relative to dynamically similar historical cases. This study demonstrates how the superposition of internal climate variability and long-term warming drives compound humid heat extremes in East Asia, providing important implications for regional climate risk assessment and adaptation strategies.