Thailand is located between 6 and 20 degrees north, and hence its southern region has an equatorial climate, with rainfall round the year, while the central and northern have a tropical monsoon climate with a marked dry and wet season. Northern Thailand is hilly with land rising up to 3000ft (1000m), while most of central and eastern Thailand consists of lowlands.

Thailand has abundant rainfall; the wet season is from May-Oct, when the country is affected by the southwest monsoon bringing warm, humid air and much cloud from the Indian Ocean.

The dry season is from Nov-April during the northeast monsoon, when winds blow overland from China or Indochina and the air is much drier. Rain then only occurs a few days each month in the north. However in the Kra Isthmus, the northeast monsoon winds bring more rain as they have blown from the Pacific Ocean and the Gulf of Siam.

In central and southern Thailand, temperatures do not differ much from month to month; but in the north temperatures are definitely cooler during the northeast monsoon. For most of the country, the hottest months are April and May before the onset of the southwest monsoon. Sunshine amounts for the wet months June-Sep average 4-5 hours a day, and 9-10 hours for the rest of the year.

Temperatures and humidity are high during the wet season, making conditions rather oppressive. However severe heat stress is rare. Conditions are fresher and usually windier during the dry season.