Thailand can best be described as tropical and humid for the majority of the country during most of the year. The area of Thailand, north of Bangkok has a climate determined by three seasons while the southern peninsular region of Thailand has only two.
In northern of Thailand the seasons are clearly defined. Between November and May the weather is mostly dry and cool, because the northeast monsoon does directly effect the northern area of Thailand. The other northern season is from May to November and is dominated by the southwest monsoon, during which time rainfall in the north.
The southern region of Thailand really has only two seasons , rainy season and hot season. These seasons do not run at the same time on both the east and west side of the peninsular. On the west coast the southwest monsoon brings rain and often heavy storms from April to October, while on the east coast the most rain falls between September and December.