Zamami Island has two quite different seasons, each with a clear draw. From January to March, humpback whales migrate to the Kerama Straits to breed, and whale watching is the main reason to come in winter. The sea is cooler and the weather can be unpredictable with occasional rough ferry crossings, but humpbacks in these numbers are rare in Asia. January and February are the peak months for whale sightings.
From May to October, the island is at its best as a beach and diving destination. Water temperatures are warm enough for comfortable snorkelling from May onwards. The peak Japanese holiday season (Golden Week in late April to early May, Obon in mid-August, and summer school holidays) fills the island and ferries to capacity — book accommodation weeks ahead. Late May and June, before the summer rush, are particularly good: warm, not yet crowded, with excellent underwater visibility.
July and August are hot and humid, with temperatures around 30–32°C. Typhoon season runs from August through October, and bad weather can disrupt ferry services at short notice. Autumn, after the typhoon risk fades in October, is a quieter but pleasant time: the beaches are less crowded, the water is still warm, and whale sightings can begin again as early as November.