Choosing between May and September in Japan depends on whether you prefer "fresh growth" or "festival heat." May is widely considered the superior month for 2026 travelers; it falls after the chaotic "Golden Week" holiday, offering mild, pleasant temperatures (20°C–24°C) and lush, vibrant green scenery before the humidity of summer hits. It is the peak of the "Green Tea" harvest and offers beautiful clear views of Mt. Fuji. Conversely, September marks the end of summer; while the heat begins to fade, it is still quite humid and is the peak of the typhoon season. This can lead to flight disruptions and heavy rain, especially in southern regions like Okinawa or Kyushu. However, September is great for those who want to experience late-summer festivals (matsuri) and lower crowds than the spring peak. If you are a first-time visitor, May is the "safer" and more comfortable bet for walking through Kyoto’s temples or Tokyo’s neon streets without the risk of a storm. If you choose September, a "pro" tip is to travel in the final week of the month when the air begins to crisp and the early autumn colors might appear in Hokkaido.