This page presents Tonga's climate context for the current climatology, 1991-2020, derived from observed, historical data. Information should be used to build a strong understanding of current climate conditions in order to appreciate future climate scenarios and projected change. You can visualize data for the current climatology through spatial variation, the seasonal cycle, or as a time series. Analysis is available for both annual and seasonal data. Data presentation defaults to national-scale aggregation, however sub-national data aggregations can be accessed by clicking within a country, on a sub-national unit. Other historical climatologies can be selected from the Time Period dropdown list. Data for specific coordinates can be downloaded for in the Data Download page.
Tonga’s climate is tropical and is defined by a wet season from November to April with moderate and variable rainfall, and a dry season from May to October. The wettest months are January, February, and March with precipitation exceeding 250 mm of rainfall per month. During the dry season, precipitation per month is less than 250 mm. The mean annual temperature in Tonga varies from 26°C to 23°C. During the wet season, the average temperature ranges from 25°C–26°C, whereas during the dry season the average temperature ranges from 21°C-24°C. Climate in Tonga and this portion of the Pacific in general is governed by a number of factors, which include the trade winds and the movement of the South Pacific Convergence Zone (SPCZ), a zone of high-pressure rainfall that migrates across the Pacific south of the equator. Year-to-year variability in climate is also strongly influenced by the El Niño Southern Oscillation (ENSO) in the south-east Pacific, which can bring prolonged drought conditions and contribute to a depletion of potable water, and tropical cyclones that occur during the wet season, causing extensive damage to local infrastructure, agriculture, and major food sources.
- Mean temperatures have increased by 0.4–0.8°C since 1970, with warming most rapid in the warmest season (November–April).
- The temperature of Ha’apai increased by 0.4°C which is much higher than the other islands of Tonga (1980 – 2014). The frequency of hot days and hot nights has increased significantly across the Pacific.
- Observations show a general decrease in annual rainfall in central and southern parts of Tonga since 1970.