On the Kii Peninsula, there are four seasons plus the rainy season. Summers are hot and humid. Fall and spring are comfortable with temperatures in the low 20s (70s for Fahrenheit). Winters are short and mild. The rainy season usually lasts from the end of June to the end of July when the temperatures ramp up and the humidity become quite uncomfortable. It is a six-week period of rainy days interspersed with sunny days.
Hiking through all seasons is possible, and careful planning is necessary to have a great experience.