September in Yamaguchi averages a daily high of 28.8°C. Expect roughly 11.2 wet days totalling 198.8mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Yamaguchi is April–May.
Based on YAMAGUCHI, JA (2.4km), 1995–2024. 25 years of September data.