Thailand enjoys a tropical climate which is influenced by seasonal monsoon winds. The southwest monsoon (May) brings a stream of warm moist air from the Indian Ocean towards Thailand, causing abundant rain over the country, especially the mountainous regions. This phenomenon is intensified through the Inter-Tropical Convergence Zone (ITCZ) in the months of May to October and tropical cyclones which produce a large amount of rainfall. The northeast monsoon, starting in October, brings cold and dry air from the anticyclone in China over major parts of Thailand, especially the northern and northeastern parts which are located at higher latitude areas. In the south, the monsoon causes mild weather and abundant rain along the eastern coast. Mean annual rainfall is 1,200-4,500 mm, with lower totals on the leeward side and higher totals on the windward side. Mean temperature is 26.3°C in the north and 27.5°C in the southern and coastal areas. Key historical climate trends are summarized below:
- Annual mean temperature anomalies indicate an increase in temperature by 1°C since 1951 in most parts.
- The frequency of extreme temperatures has increased since 1951, especially in the coastal region of the country.
- In the year 2015, the annual mean temperature of 27.9°C indicated a 0.8°C increase compared to average temperatures. It was Thailand’s second warmest year in 65 years record.
- March to May is the hottest period of the year, maximum temperatures usually reach 40°C or more. The onset of the rainy season also significantly reduces the temperatures starting in mid-May with temperatures of 40°C and lower. During the winter, the outbreaks of cold air from China occasionally reduces temperatures to fairly low values, especially in the Northern and Northeastern parts to near or below 0°C.
Most areas of the country receive 1,200 to 1,600 mm per year. Some areas on the windward side, particularly Trat province in the Eastern Part and Ranong province in the Southern Thailand West Coast receive more than 4,500 mm a year. Annual rainfall less than 1,200 mm occurs in the leeward side areas in the central valleys and the uppermost portion of the south.
This section provides the options to visualize historical climate data for different timeframes via map and annual cycle chart.