Well, the summer in Japan starts from June and ends in August. But, there are some parts of the country, which is pretty much warmed up in as early as April and won’t cool down at least before September. On the other hand, there are some other places which will stay chilly up until June. No matter whatever kind of weather you are expecting, it will solely depend on the exact destinations you are working on. If this is your first time in Japan, then some of the spots that you will add in your checklist will be Kyoto, Tokyo and Osaka.
Some of the other parts:
In most parts of the country, from June to middle of July, you will experience some heavy rainfall. Okinawa is the place, which gets the most precipitation a month before than the rest of the Japan. On the other hand, you have the Hokkaido and the Ogasawara Islands, which are not going to be, get affected by the rainy seasons much. But, the rain season will not mean that you will be going through some big monsoon time for several days to come.
The June time and more:
Even though June is that time of the year in Japan, when you might get substantially wet, but the rainy season over here is comparably mild to the rest of the Asian countries. So, even if you run into that inclement weather, you are likely to experience sudden downpour, which will end as quickly as they have started. Or you might face the misty drizzle for the entire day. So, you can get out of your hotel room and explore the city even if it is raining. Chances are high that it will stop soon!