Record‐Breaking Humid Heat in Northern China During Summer 2025 Driven by Kuroshio–Oyashio Extension SST Anomalies

Abstract A record‐breaking humid‐heat event occurred over northern China during 24 June–13 July 2025, characterized by persistent extreme wet‐bulb temperatures. The event is associated with a strong and persistent positive geopotential height anomaly, which favors the accumulation of heat and moisture. Further analyses reveal that warm sea surface temperature (SST) anomalies over the Kuroshio–Oyashio Extension (KOE) enhance upward turbulent heat fluxes, reducing lower‐tropospheric meridional temperature gradients and baroclinicity, and suppressing transient eddy activity. The associated reduction in transient eddy vorticity forcing favors positive geopotential height anomalies over the KOE, providing a dynamically consistent pathway linking SST anomalies to the large‐scale circulation. Sensitivity experiments with the Community Atmosphere Model version 5 (CAM5) reproduce the key circulation response. These results suggest that KOE SST anomalies likely contributed to the development of this extreme humid‐heat event by shaping a favorable anomalous circulation background.