Tonga is one of few places where humpback whales can be swum with by snorkellers, between Vava'u's protected harbour and the Ha'apai atolls' calm channels July through October.
Humpback whale-swimming season with calves visible on calm days off Vava'u and Ha'apai, and dive operators run multiple trips daily.
Whales arriving and the country in its dry-season calm, with Tongatapu's archaeological sites at the Ha'amonga Trilithon comfortable to explore.
Cyclone season with January-March highest risk, whales gone south, and many smaller island lodges close. Tongatapu accessible year-round.
Whale season at peak with calves at maximum size and confidence, and the Heilala Festival in late June-early July aside, the kingdom is active.