When one should visit Japan is based on more than weather conditions but it is certainly an influential factor. Below you will get a brief overview of the weather in Japan.
Basically Japan has four seasons. Winter months are December – February, spring months are March – May, summer months are June – August and autumn months are September – November. The average temperature in Japan is however 5.1 °C (41.2 °F) during the winter and 25.2 °C (77.4 °F) during the summer months.
Important to know is that the climate in Japan changes with the latitude. Specially if you plan to visit Ryukyu Islands (Okinawa is amongst them) as the climate here is quite different from the rest of Japan. This region has a subtropical climate.
Also, the rain season usually starts in early May and lasts until late July. The rain season moves from Ryukyu Islands in the south to Hokkaido in the north. The Kansai area and Tokyo area is usually hit during the beginning of July.
When to go?
Well Japan has a lot to offer all year around. Festivals (matsuri) and events takes place regularly. Bear this in mind when you make your decision. But if you are referring to the climate, a lot of people enjoys the weather in Japan during spring and autumn. The climate is quite pleasant during this seasons due to the temperature and the relatively low humidity.
Spring and autumn can however be a difficult time for some people to travel. It may be hard to get off from work and other stuff that ties one down. So that leaves you with the Christmas holidays or summer vacation. During the Christmas holidays weather in Japan will be colder but manageable if you dress right. Summer on the other hand might be harder to handle for some people. Temperature rises and rainfall increases which leads to a very humid climate. It still possible and popular to visit Japan during the summer. You should however perhaps plan your trip so you miss the as much of the rain season as possible.