Tonga has a marine tropical climate characterised by hot, wet, summers and warm winters. The mean annual rainfall ranges from about 1600 mm in the South (‘Eua) to around 2300mm in the North (Niuafo’ou) with a marked summer maximum (December - April) and a winter minimum (June - September). Rainfall is generally adequate for the growth of plants throughout most years, but droughty periods can occur, particularly in winter and in the southern islands.
High-intensity, short-duration rainfall can occur, especially during the cyclone season (December - March) and is of particular significance to agriculture, severely damaging crops and causing soil erosion.
The mean annual air temperature ranges from about 23.7°C in Tongatapu to about 26.6°C in Niuafo’ou.