Samui really doesn’t have any rigid seasons like in Europe, Australia or Northern America. This is a tropical climate, the temperature ranges from low twenties to low thirties all year round. The temperature might not vary too much but the humidity does, and this does make a big difference to how a temperature may feel. 32°C/89°F, dry and low humidity feels much more enjoyable than the same temperature with very high humidity.
Also we do not have a monsoon season at the same time as Phuket, this is often misunderstood by tourists before traveling to Samui. In fact our apparent monsoon or rainy season usually amounts to some wind and sporadic showers mixed with sunny days in November.
As far as rain goes, you can expect it any time here, but usually it is brief and sunshine is not too far behind. Sometimes it’s a welcome relief from the heat, and the storms we get can be really entertaining. There’s nothing better than taking shelter in a beachside bar and enjoying a beer while watching nature’s light show over the sea.
Source: World Weather Information Service: Koh Samui, Thailan
Although there aren’t traditional seasons, there are climatic differences throughout the year.
Dry Season (High Season).
Mid-December – February
The high season on the island, is as much to do with it being holiday season for visitors as it is the weather. The weather at this time of year is more often than not 7 days of sunshine, with some rain in December and sometimes a refreshing breeze. December would be the coolest as the temperature gradually increases from the start of the year. It’s a great time to holiday here, the average high is 30°C/86°F and average low is 24°C/75°F. If you really want to reduce the chance of being affected by rain visit after the New Year, the wet monsoon can run beyond mid-December, sometimes into the New Year. As far as busy goes, this is the peak season.
March – August
The high season runs on to the end of April. March and April are the hottest months of the year, with consistent highs of 34°C/93°F and minimums of 25°C/77°F. The days are hot with little rain to speak of. Come May we start to see some rain as a welcome relief from the hot days. The rain normally amounts to a late afternoon thunderstorm only. April, May and June are the most humid months of the year. July and August cools down a little, but it’s a minimal change. The tides are low around the island at this time of year, which means plenty of beach.
September – Mid-December
The weather starts to cool down a little in September, it’s still hot though. Afternoon and evening storms become more prevalent. October is more of the same, with more chance of rain. The wind starts to pick up from the northeast and the sea can get a little rough. November is the wettest time of the year here, with winds and the coolest weather of the year. It is the quietest time on the island, some businesses decide to have rest in this month and close up. If you are looking for a bargain holiday you’ll find some pretty good deals this time of year. There’s a very good chance you’ll have sunny days and calm weather, you just never know. As mentioned above, the wet season here is mostly rain showers and some wind in between sunny days! Temperatures average between 30°C/86°F and 24°C/75°F.