The weather in Ko-Samui is slightly different to the weather in Phuket as Phuket is situated in the Andaman Sea and Koh-Samui lies in the Gulf of Thailand.
The three months of British winter are the best three months to spend a holiday in Ko-Samui.
THE DRY SEASON: December to March
The Koh-Samui dry season is from December through to early March and during December, an average of 98mm of rain falls. In January the average rainfall is only a maximum of 38mm and in February, the average rainfall in Ko-Samui is 8mm. There is often a cooling breeze although the maximum average temperature is only about 31 Celsius. At night, the average minimum temperature is a balmy 23 Celsius. The amount of sunlight during December, January and February is the maximum for Ko-Samui, and the temperature of the sea is a fantastic 27 Celsius.
THE HOT SEASON: April to August
The hot season for Ko-Samui is not very much hotter than the dry season. The hot season starts in mid March and continues on until August. The maximum average temperature during the hot season is 33 Celsius and the average minimum temperature is 25 Celsius. In April the average rainfall is 62mm and in May it is 186mm. During the months of June, July and August the average rainfall per month is about 123mm. Although it rains a bit in May, this is a fabulous time to visit Thailand as it is very sunny and the sea is a warm 28 Celsius.
THE RAINY SEASON: September to November
The rainy season is usually from September to November and in November there is an average of 302mm of rain. Usually the rain showers are quite short but they are vital for the island’s tourist economy as water supplies are finite. During the rainy season the average temperature during the day is 31 Celsius and the average night time temperature is 24 Celsius. Swimming in the rain is not so bad especially when the sea water temperature is 28 Celsius. And, when the rain stops, the sun quickly reappears and dries everything up.