Average TempDay 31°C Night 25°C
Koh Samui has a tropical climate and is warm all year-round with average temperatures of 28-32°C. The hours of sunshine per day depends on the time of year, and averages at around 7 hours. Koh Samui doesn’t experience the south-west monsoon that affects the majority of Thailand, so between May and September it’s a better option for warm and dry weather than Phuket and Khao Lak on the Andaman Coast. Instead, it has its own rainy season between October and December, when the weather is largely warm and wet. Most travellers head for Koh Samui between December and April when days are warm and dry.
January is warm and dry on Koh Samui. There’s an average temperature of around 26°C and 7 hours of sunshine a day. January is peak season in Thailand because the weather is great across the country, so it’s a good time to combine Koh Samui with a stopover in Bangkok and visit the beautiful cities of Chiang Mai and Chiang Rai in Northern Thailand.
Koh Samui has lovely warm and dry weather in February with minimal rain expected. There are 8 hours of sunshine per day and warm sea temperatures of around 27°C, making it one of the best months for sunbathing and enjoying Koh Samui’s white-sand beaches.
March is a great month to visit Koh Samui, when there is plenty of warm and dry weather and days are generally filled with blue skies. Temperatures average between 26-31°C and there are 8 hours of sunshine each day.
Days are hot and humid in Koh Samui in April. It’s one of the hottest months in Koh Samui as well as the rest of Thailand, with average temperatures of between 27°C and 33°C. There are 8 hours of sunshine every day and the sea is warm at around 28°C. If you’re travelling around Thailand, it’s worth bearing in mind that April tends to be sweltering across the country.
The Thai New Year, Songkran, is a three-day national celebration in April, most notably marked by the huge street water fights – a welcome refreshment from the scorching heat.
Koh Samui’s weather in May is hot and sunny with some rain expected. Days are likely to be hot and dry with the occasional shower. Average temperatures are around 26-33°C and there are around 7 hours of sunshine a day.
June is a great month to visit Koh Samui, where there is little rain and days are hot and sunny. As conditions become increasingly wet around the rest of Thailand, Koh Samui remains mostly dry with an average temperature is 29°C and warm seas at around 28°C.
Koh Samui is warm and mostly dry in July – the best option in Thailand during school summer holidays as other regions of Thailand will have high chances of rainfall. Temperatures average at around 29°C and there’s 6 hours of sunshine a day. There may be some rainfall, although this usually occurs in short, afternoon showers which tend to clear up quickly.
August is a good month to visit Koh Samui in the school summer holidays. The rest of the country has high chances of rain, so for beaches and warm weather it’s a much better option if you’re visiting Thailand. There’s an average temperature of 29°C and warm sea temperatures of 28°C.
September is warm in Koh Samui with a moderate chance of rainfall. As Koh Samui’s rainy season approaches, you can expect more rain than in previous months which usually falls in sharp showers and often tends to alternate with days of sunshine. September is noticeably quieter on Koh Samui as the school holidays end, so it could be a good time to take advantage of the fewer crowds and great-value offers.
October is warm, wet and humid in Koh Samui. As the Gulf of Thailand is affected by the north-east monsoon, there’s a high chance of rainfall throughout the month and sea conditions can be rough. If you don’t mind relaxing in your resort while it rains, you can still enjoy warmth with an average temperature of find some of Koh Samui’s best-value offers in the low season. If you’re travelling in October but want plenty of sunshine, we recommend Bali which is hot and has a much lower chance of rainfall.
Koh Samui’s weather is wet and humid in November. The weather remains warm with an average temperature of 27°C and plenty of rain and thunderstorms can be expected throughout the month. For a higher chance of sunshine and better sea conditions, Phuket and Khao Lak on the Andaman coast have drier and sunnier weather in November.
Loy Krathong Festival takes place on the night of the full moon in November. It’s a celebration where people can let go of negative feelings by floating symbolic krathongs, small offerings traditionally made from banana leaves, and letting off lanterns into the sky.
Koh Samui is warm and humid in December with a reasonable chance of rainfall. The average temperature is 27°C and you can expect showers as Koh Samui’s rainy season starts to subside. Phuket and Khao Lak on the Andaman Coast are better options for warm, sunny weather.