By Kylian Dev
Koh Samui in January
Some rainAverage highs of 29°C and lows of 24.2°C, with 127 mm of rain over about 9 days. Some showers, usually short: still a good month to go.
Weather
Weather in Koh Samui: the climate month by month
When to go to Koh Samui, how hot it gets and when the rain comes: every month in detail, from the official climate averages of the Thai Meteorological Department, with my own advice on top.
- Official 1991–2020 averages
- 12 months in detail
- Best time: January to September
In short
The best time to visit Koh Samui is January to September, the driest period of the year. The rainy season runs from October to December, and the wettest month is November, with 445 mm of rain over about 17 days. Daytime highs range from 29°C in January to 32.9°C in May, and nights never drop below about 24°C on average.
At a glance
Rain and temperatures in Koh Samui, month by month
Bars show average rainfall; figures above them are the average daytime high and night-time low.
29°24°
127Jan
29°25°
64Feb
30°25°
116Mar
32°26°
83Apr
33°26°
132May
33°25°
134Jun
32°25°
117Jul
32°25°
102Aug
32°25°
118Sep
31°24°
295Oct
30°24°
445Nov
29°24°
263Dec
Month by month
Climate table for Koh Samui
Click a month to see what else happens in Thailand that month: festivals, crowds and the best regions.
| Month | High | Low | Rain | Rainy days | Humidity | Verdict |
|---|---|---|---|---|---|---|
| January | 29 °C | 24.2 °C | 127 mm | 9 | 83 % | Some rain |
| February | 29.4 °C | 24.9 °C | 64 mm | 4 | 81 % | Dry |
| March | 30.4 °C | 25.4 °C | 116 mm | 5 | 81 % | Some rain |
| April | 31.8 °C | 26 °C | 83 mm | 6 | 81 % | Dry |
| May | 32.9 °C | 25.7 °C | 132 mm | 11 | 80 % | Some rain |
| June | 32.7 °C | 25.3 °C | 134 mm | 10 | 78 % | Some rain |
| July | 32.3 °C | 25.1 °C | 117 mm | 11 | 78 % | Some rain |
| August | 32.4 °C | 25.1 °C | 102 mm | 11 | 78 % | Some rain |
| September | 31.9 °C | 24.8 °C | 118 mm | 11 | 80 % | Some rain |
| October | 30.6 °C | 24.3 °C | 295 mm | 16 | 85 % | Rainy |
| November | 29.7 °C | 24.1 °C | 445 mm | 17 | 86 % | Rainy |
| December | 29.3 °C | 24 °C | 263 mm | 12 | 83 % | Rainy |
Total rainfall over the year: 1,996 mm.
Month by month
Koh Samui in each month of the year
Koh Samui in February
DryAverage highs of 29.4°C and lows of 24.9°C, with 64 mm of rain over about 4 days. A dry month: one of the best times to go.
Koh Samui in March
Some rainAverage highs of 30.4°C and lows of 25.4°C, with 116 mm of rain over about 5 days. Some showers, usually short: still a good month to go.
Koh Samui in April
DryAverage highs of 31.8°C and lows of 26°C, with 83 mm of rain over about 6 days. A dry month: one of the best times to go.
Koh Samui in May
Some rainAverage highs of 32.9°C and lows of 25.7°C, with 132 mm of rain over about 11 days. Some showers, usually short: still a good month to go.
Koh Samui in June
Some rainAverage highs of 32.7°C and lows of 25.3°C, with 134 mm of rain over about 10 days. Some showers, usually short: still a good month to go.
Koh Samui in July
Some rainAverage highs of 32.3°C and lows of 25.1°C, with 117 mm of rain over about 11 days. Some showers, usually short: still a good month to go.
Koh Samui in August
Some rainAverage highs of 32.4°C and lows of 25.1°C, with 102 mm of rain over about 11 days. Some showers, usually short: still a good month to go.
Koh Samui in September
Some rainAverage highs of 31.9°C and lows of 24.8°C, with 118 mm of rain over about 11 days. Some showers, usually short: still a good month to go.
Koh Samui in October
RainyAverage highs of 30.6°C and lows of 24.3°C, with 295 mm of rain over about 16 days. A rainy month: expect a shower most days and keep plans flexible.
Koh Samui in November
RainyAverage highs of 29.7°C and lows of 24.1°C, with 445 mm of rain over about 17 days. A rainy month: expect a shower most days and keep plans flexible.
Koh Samui in December
RainyAverage highs of 29.3°C and lows of 24°C, with 263 mm of rain over about 12 days. A rainy month: expect a shower most days and keep plans flexible.
Seasons
The three things to know about the weather in Koh Samui
Best time
January to September. Least rain of the year, calmer sea on the coast and lots of sunshine. It is also the high season: book early.
Rainy season
October to December. Rain usually comes as heavy showers, often in the afternoon or at night, rather than all day. Peak in November (445 mm).
Hottest month
May, with average highs of 32.9°C and high humidity. Plan outdoor visits early in the morning.
My advice
What the numbers don't say about Koh Samui
Samui does not follow the rest of Thailand. It is at its best from January to September, including July and August, when it rains a lot on the Andaman coast. The real rainy season is October to December, with November the wettest month: the sea gets rough and ferries can be cancelled. If you travel in summer, choose Samui over Phuket.
Where these figures come from
Monthly averages over 1991–2020 from the Ko Samui weather station of the Thai Meteorological Department, as published in the World Meteorological Organization climate normals. They describe a typical year, not a forecast: a given year can be wetter or drier.
Data table (Wikipedia, WMO/TMD normals)FAQ
Weather in Koh Samui: your questions
When is the best time to visit Koh Samui?
January to September is the best time: it is the driest period of the year in Koh Samui, with the most sunshine. It is also the busiest and most expensive season, so book early.
Where to stay in Koh SamuiWhen is the rainy season in Koh Samui?
The rainy season runs from October to December. The wettest month is November, with about 445 mm of rain over 17 days on average. Showers are heavy but often short: add a light rain jacket to your Thailand packing list.
What is the hottest month in Koh Samui?
May is the hottest month, with average highs of 32.9°C. The most pleasant month for temperatures is January, with highs of 29°C.
Is it worth going to Koh Samui in the rainy season?
Yes, if you stay flexible. Prices drop, there are fewer tourists and the scenery is green. Expect a shower most days, allow spare days for boat trips and get travel insurance that covers cancellations.
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