The Cold Season:
November to February – you can be excited and see frost occasionally in Chiang Rai and Chiang Mai in the north where the temperature may fall to as low as 4°C but the south remains warm. January is the best month to be in Bangkok.
The Hot Season:
February to May will give you sunny days with little rain and temperatures will be around the 29°C mark. The months of April and May are the hottest. You may get a bit of rain during this season in the southern provinces.
The Rainy Season:
Of course, if you go in the monsoon season, that is technically from May to October you may have a chance of experiencing cabin fever, as sometimes the rains keep on coming. Other days it may be a case of blazing sunshine for a few hours relief to the deluge. Bangkok becomes a hot pool and quite often experiences flooding during this period, hence its nickname of “Venice in the East”.