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Variation of the western North Pacific subtropical high (WNPSH) is an important meteorological factor for determining summertime rainfall and temperature over East Asia. Here, three major modes of summertime WNPSH variability are identified and corresponding environmental changes are investigated using cyclostationary empirical orthogonal function analysis. The leading mode exhibits a clear reinforcement ofWNPSH associated with global warming. The second and third modes are characterized by intra-seasonal variation of the WNPSH intensity related to sea surface temperature variability in the central and eastern equatorial Pacific. Although WNPSH variability is regarded as a local manifestation, it reflects much wider changes in the entire North Pacific. The three modes exert seasonally and geographically distinct impacts on the East Asian weather by setting anomalous atmospheric circulation and altering the direction of moisture and heat transport. As such, the leading WNPSH modes are an important indicator of summertime weathers in countries neighboring the western North Pacific. This study also shows that extreme weather events are likely to increase as global warming intensifies.