November to March is the high season in Thailand where the weather is cooler and dry and this is when most tourists visit the Kingdom. By April the temperature becomes very hot. By May the rainy season begins and lasts to November. The inland provinces have the monsoon rains throughout the rainy season. On the west coast around Phuket the storms last between April to October. Around Koh Samui on the east coast of the Gulf of Thailand the storms occur between September to December.
In most areas average temperatures range from 23(C) 73(F) at night to around 32(C) 90(F) during the day between November to February. March to July has very hot average temperatures of 26(C) 79(F) at night to 36(C) 97(F) during the day. August to October has hot mid range temperatures.
Humidity and air temperature is far less in the northern provinces during the peak tourist season of November to March than it is at the same time around Bangkok and Pattaya in the south. Bangkok can reach 80%+ humidity in September and October. On the mountains bordering Laos in the north east provinces around such resort areas as Phu Chi Fa forest park it can be very cold at night.
February Dry and cooler with the end of the peak tourist season.
March Average temperatures begin to increase.
April Hot temperatures. Wet monsoon period begins for the west coast of Thailand and throughout the inland regions. Dry in other areas.
May -June Rainy season begins with hot temperatures.
July -August Rain and hot temperatures.
September Rain with mid range temperatures.
October End of rainy season and temperatures begin to cool. Monsoon period ends for the west coast of Thailand and the inland areas. Stormy season begins on the east coast of Thailand.
November Dry and cooler temperatures and the start of the peak tourist season.
December Peak tourist season and the end of the stomy season on the east coast of Thailand.