Japan Weather In September 2025. August 25, 2025 at 9:12am edt. Average monthly weather with temperature, pressure, humidity, precipitation, wind, daylight, sunshine, visibility, and uv index.

Autumn gradually cools down, with temperatures in september ranging from about 20°c to 25°c (68°f to 77°f), decreasing to highs of 14°c to 18°c (57°f to 64°f) by november. Average temperatures range from 20°c (68°f) to 27°c (81°f).