Summer: June, July & Aug 夏
The weather in June is nice until tsuyu (the rainy season) sweeps up the country from the southwest with its tsuyu zensen (rainy season front).
Tsuyu is not a great time for travel, unless you’re heading for Hokkaidō, which historically and famously doesn’t have a rainy season..... though many believe that tsuyu has now reached Hokkaidō due to climate change.
Tsuyu generally passes by July 20. Keen hikers believe that tsuyu-ake-tōka (the first 10 days after tsuyu passes) is the best time for good weather to hit the high mountain trails.
Beaches, the cooler mountains and Hokkaidō become welcome escapes once the hot, humid summer (natsu) hits Japan. Many mountain resorts run music festivals, including the legendary Fuji Rock Festival at Naeba.