Extratropical cyclogenesis occurs off the coast of China, over the East China Sea and surrounding areas, as a result of cold-air outbreaks from the mainland about every five days, on the average, during winter months. Many of these storms subsequently propagate northeastward into the Pacific, and in the process they have a substantial impact on the weather of highly populated areas of northeast China, the Koreas and Japan. This paper presents a climatological analysis of this cyclogenesis for the period 1899–1962 based on U.S. Weather Bureau historical weather maps. The averaged seasonal variability during the period is discussed in some detail with comparisons to sea-surface temperature variability, taken from the Historical Sea‐Surface Temperature Project data, revealing that the meridional gradient of sea surface temperature across the East China Sea plays a significant role in the annual cycle of cyclogenesis. In contrast, wind speed, air–sea temperature difference and averaged heat fluxes sh... Abstract Extratropical cyclogenesis occurs off the coast of China, over the East China Sea and surrounding areas, as a result of cold-air outbreaks from the mainland about every five days, on the average, during winter months. Many of these storms subsequently propagate northeastward into the Pacific, and in the process they have a substantial impact on the weather of highly populated areas of northeast China, the Koreas and Japan. This paper presents a climatological analysis of this cyclogenesis for the period 1899–1962 based on U.S. Weather Bureau historical weather maps. The averaged seasonal variability during the period is discussed in some detail with comparisons to sea-surface temperature variability, taken from the Historical Sea‐Surface Temperature Project data, revealing that the meridional gradient of sea surface temperature across the East China Sea plays a significant role in the annual cycle of cyclogenesis. In contrast, wind speed, air–sea temperature difference and averaged heat fluxes sh...