Tonga is an archipelago directly south of Western Samoa. Its 169 islands, 96 of them inhabited, are divided into three main groups--Vava'u, Ha'apai, and Tongatapu--and cover an 800-kilometer (500 mi.)-long north-south line. The largest island, Tongatapu, on which the capital city of Nuku'alofa is located, covers 257 square kilometers (99 sq. mi.). Geologically the Tongan islands are of two types: most have a limestone base formed from uplifted coral formations; others consist of limestone overlaying a volcanic base.

The climate is basically subtropical with a distinct warm period (December-April), during which the temperatures rise above 32^oC (90^oF), and a cooler period (May-November), with temperatures rarely rising above 27^oC (80^oF). The temperature increases from 23^oC to 27^oC (74^oF to 80^oF), and the annual rainfall is from 170 to 297 centimeters (67-117 in.) as one moves from Tongatapu in the south to the more northerly islands closer to the Equator. The mean daily humidity is 80%.