The best months to visit Japan are May and August. See monthly temperatures, rainfall and rain days (1991–2020 averages) to plan your trip.
Average daytime high and monthly rainfall in Japan: January 4°C / 67mm; February 5°C / 63mm; March 6°C / 114mm; April 17°C / 114mm; May 19°C / 131mm; June 22°C / 164mm; July 27°C / 151mm; August 27°C / 114mm; September 25°C / 185mm; October 19°C / 211mm; November 12°C / 91mm; December 5°C / 60mm.