Okinawa is subtropical, which means mild winters and hot, humid summers. Cherry blossoms arrive here first in Japan -- as early as late January -- making it an unexpectedly good winter destination by Japanese standards.
The rainy season (tsuyu) typically runs from mid-May through June, with heavy downpours that can last days. July through September is peak beach season but also typhoon season; storms can disrupt travel plans with little warning. The sweet spot for most visitors is late March through April or October through November, when the weather is warm, the humidity manageable, and the crowds thinner.
The Hija River Koi-nobori Festival in late April sees roughly 500 carp-shaped streamers strung along the river to celebrate children's health -- a colourful sight if your visit coincides. The Okiten art exhibition, held annually since 1949, is Okinawa's largest art show, typically in March.