While many people associate the "Rainy Season" (Tsuyu) with June, the month that often sees the most rainfall across major Japanese cities like Tokyo and Osaka is actually September or October. This is due to the typhoon season, which peaks in late summer and early autumn. While June features frequent, lighter "monsoon" rains and high humidity, the storms in September can bring massive, concentrated downpours over a shorter period. In some years, October can also take the title if a particularly late typhoon hits the coast. Conversely, the northern island of Hokkaido is largely unaffected by the Tsuyu rainy season in June, making it the driest part of the country during early summer. If you are looking for the absolute driest time to visit, December and January offer crisp, clear skies across most of the main island of Honshu.