It depends on where in the country. Hokkaido is spectacular. The Tohoku area can be good as well. But for the places you mention, the humidity especially can be brain crushing and make you want to die. read more
You are correct about being concerned about the humidity. Phoenix’s humidity in August - September is in the neighborhood of 20%. Nagoya is in the 80% neighborhood. That's quite a difference. That's enough of a difference to make your hair curl. It won't be as hot as Arizona, but the humidity will make you wonder if you're even on the same planet. read more
Late August (unconfirmed) A large dance festival of more than 20,000 dancers in Nagoya. Dancers from all over Japan (and a few international teams) show off the traditional music, dance and clothing of their hometowns. read more
The average sea temperature in and around Tokyo in August is 26°C (79°F). Tokyo sunrise & sunset times for August 2018 Browse the sunrise & sunset times for Tokyo in August 2018. read more