Located in Oceania, Tonga is a small archipelago in the South Pacific Ocean, directly south of Samoa and about two-thirds of the way from Hawaii to New Zealand. It has 169 islands, 36 of them inhabited, which are in three main groups – Vavaʻu, Haʻapai, and Tongatapu – and cover an -long north–south line. The total size is just . Due to the spread out islands it has the 40th largest Exclusive Economic Zone of . The largest island, Tongatapu, on which the capital city of Nukualofa is located, covers . 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. Climate The climate is tropical with a distinct warm period (December–April), during which the temperatures rise above , and a cooler period (May–November), with temperatures rarely rising above . The temperature increases from , and the annual rainfall is from as one moves from Tongatapu in the south to the more northerly islands closer to the Equator. The average wettest period is around March with on average . The average daily humidity is 80%. Cyclones can occur from October to April. Geology Though administratively divided into the three main island groups of Tongatapu, Ha'apai, and Vava'u (excluding the outlying islands), the Tonga archipelago is actually made of two geologically different parallel chains of islands. The western islands, such as ʻAta (also known as Pylstaart island), Fonuafo'ou, Tofua, Kao, Lata'iki, Late, Fonualei, Toku, Niuatoputapu, and Tafahi, make up the Tongan Volcanic Arc and are all of volcanic origin. They were created from the subduction of the westwards-moving Pacific plate under the Australia-India plate at the Tonga Trench. The Tongan Islands sit on the Australia-India plate just west of the Tonga Trench. These volcanoes are formed when materials in the descending Pacific plate heat and rise to the surface. There is only limited coral reef development on these islands, except for Niuatoputapu. The eastern islands are not volcanic and sit above the mostly submerged Tonga ridge that runs parallel to the Tongan Volcanic Arc and the Tongan Trench. Of these islands, only 'Eua has risen high enough to expose its underlying Eocene volcanic bedrock, the rest are either low coral limestone islands (Tongatapu, Vava'u, Lifuka) or sand cay islands ('Uoleva, 'Uiha). These islands are surrounded by "a protective and resource-rich labyrinth of fringing, apron and