Weather Thailand – Monsoon Seasons
South-West Monsoon – May to October effecting the West coast (Phuket)
North-East Monsoon – November to March effecting the East coast (Koh Tao, Koh Samui)
The Monsoon brings about routine flooding in the north, north east and central regions, often causing mudslides and flash floods; visitors planning to trek in the jungle during this time should check conditions with licensed tour guides before leaving. Phuket can have flooding but thats most of the time temporarily and does not affect tourism and divers.
The cool season, the favored weather Thailand for most visitors, runs from November to February. Bangkok has a hot, tropical climate with daytime temperature reaching the mid-30s Celsius throughout the year. November to February is the driest time of year and the most popular with tourists. March, April and May are the hottest months, and the rainy season runs from May to October, of which October is the wettest.
Temperatures in the capital, Bangkok, range between 68°F (20°C) in December and 95°F (35°C) in April. January and February are normally dry, March to May is the hottest time of year, June to October tends to be the wettest season (with 90% of the country’s rainfall occurring in this period), and November and December are the coolest months.
As the rest of the planet, the weather is definitely changing over time. The seasons are not as clear as they used to be. For sure the hottest time is still the same, from March-May. And no matter if its raining or not, Thailand is still one of the better countries to spend your holidays in and rain or no rain, you can dive in Thailand 365 days a year with a average temperature of 27 Celsius.