Tropical Climate with Sunny Day

 

Map of Thailand weather (Source: Thai Meteorological Dept)

 

The climate of Thailand is under the influence of monsoon winds of seasonal character : southwest monsoon and northeast monsoon. The southwest monsoon which starts in May brings a stream of warm moist air from the Indian ocean towards Thailand causing abundant rain over the country, especially the windward side of the mountains. Rainfall during this period is not only caused by the southwest monsoon but also by the Inter Tropical Convergence Zone (ITCZ) and tropical cyclones which produce a large amount of rainfall. May is the period of first arrival of the ITCZ to the Southern parts. It moves northwards rapidly and lies across southern China around June to early July that is the reason of dry spell over upper Thailand. The ITCZ then moves southerly direction to lie over the northern and northeastern parts of Thailand in August and later over the central and southern parts in September and October, respectively. The northeast monsoon which starts in October brings the cold and dry air from the anticyclone in China mainland over major parts of Thailand, especially the northern and northeastern parts which are higher latitude areas. In the southern parts, this monsoon causes mild weather and abundant rain along the eastern coast of the part.

The onset of monsoons varies to some extent. Southwest monsoon usually starts in mid-May and ends in mid-October while northeast monsoon normally starts in mid-October and ends in mid-February.

From the meteorological point of view the climate of Thailand may be divided into three seasons as follows :

Rainy or southwest monsoon season (June - October). The southwest monsoon prevails over Thailand and abundant rain occurs over the country. The wettest period of the year is August to September. The exception is found in the southern Thailand east coast(Thai Gulf coast) where abundant rain remains until the end of the year that is the beginning period of the northeast monsoon and November is the wettest month.

Winter or northeast monsoon season (November - February). This is the mild period of the year with quite cold in December and January in upper Thailand but there is a great amount of rainfall in southern Thailand east coast(Thai Gulf coast).

Summer or pre-monsoon season (March - May). This is the transitional period from the northeast to southwest monsoons. The weather becomes warmer, especially in upper Thailand. April is the hottest month.