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Tonga is an archipelago in the South Pacific consisting of 169 islands, 36 of them inhabited, and is divided into three main groups – Vava'u, Haʻapai, and Tongatapu, which together cover an 800-kilometre (500 miles)-long north–south line. The largest island, Tongatapu, on which the capital city of Nuku'alofa is located, covers 257 square kilometres (99 sq mi). Geologically, the Tongan islands are generally comprised of two types: volcanic islands rising directly from the ocean floor (e.g. Kao and Tofua in the Haʻapai group), and seismically uplifted coral limestone islands overlaying an older volcanic base (e.g. Tongatapu). The active volcanic islands are situated in an approximate north-south line located west of the more populated islands. A new volcanic island broke the ocean's surface in the Haʻapai group during the 1990s.
The climate is basically subtropical with a distinct warm period (December–April), during which the temperatures rise above 32 °C (90 °F), and a cooler period (May–November), with temperatures rarely rising above 27 °C (80 °F). The temperature increases from 23 °C to 27 °C (74 °F to 80 °F), and the annual rainfall is from 1700 to 2970 millimetres (67 to 117 in) as one moves from Tongatapu in the south to the more northerly islands closer to the Equator. The mean daily humidity is 80%.
