Tonga’s current climate has a marked diurnal, seasonal and spatial variation in temperature. Mean annual temperatures vary according to latitude from 27°C at Niuafo’ou and Keppel (northernmost island) to 24°C at Tongatapu (in the south). Diurnal and seasonal variations can reach as high as 6°C throughout the island group. There is also a marked seasonality in the rainfall of Tonga between hot wet (November–April) and cool dry (May–October) seasons. The annual mean (1971–2007) rainfall for the five meteorological stations in Tonga show Tongatapu received on average of 1,721 mm, Vava’u 2,150 mm, Ha’apai 1,619 mm, Niuafo’ou 2,453 and Niua Toputapu 2,374 mm.
Niuafo’ou is both the wettest and the northernmost island of the Tongan archipelago located closer to the wet tropics and influenced by both the Intertropical Convergence Zone and the South Pacific Convergence Zone (SPCZ). The Ha’apai group receives the lowest rainfall due to its positioning between influence of SPCZ over northern Tonga and regions to the south, which come under the influence of the upper air jet stream and other extra tropical features.
For more valuable Climate Science Information, the Pacific Climate Change Science Program (PCCSP) has created a rigorously researched, peer-reviewed scientific assessment of the climate of the western Pacific region. Building on the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, the PCCSP has created a two volume publication, Climate Change in the Pacific: Scientific Assessment and New Research, which represents a comprehensive resource on the climate of the Pacific.
The first volume of Climate Change in the Pacific: Scientific Assessment and New Research provides a regional overview of climate change across the Pacific Climate Change Science Program (PCCSP) region, and includes annual and seasonal climatology, variability and long-term trends, methodology, climate model evaluation, and projected changes in atmospheric and oceanic variables from global and downscaled climate models. Volume 2 presents individual country reports which provide country-specific projections and relevant climate information.
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