Climate Overview
The climate in Ko Samui is hot. The average annual temperature is 28°C and approximately 1723mm of precipitation falls per year. Ko Samui receives a notable amount of rainfall throughout the year, including during its driest month. Ko Samui sits near the equator, so seasonal temperature differences are minimal throughout the year.
Temperature
Ko Samui has relatively stable temperatures year-round, staying within a 4°C range. The warmest month is May, when average highs reach 30°C and the mean temperature sits around 29°C. December is the coolest month, with minimum temperatures around 26°C and an average of 27°C. Daily temperature variation is modest, with an average difference of 2°C between highs and lows.
Precipitation
Ko Samui is a fairly wet location, receiving approximately 1723mm of precipitation annually, which averages out to around 144mm per month. The wettest month is November, averaging 263mm of rainfall. October and December also tend to see above-average precipitation. The driest month is March, with just 37mm. That's 226mm less than November, the wettest month. Rainfall is heavily concentrated in certain months, creating a distinct wet and dry season. Visitors should plan around these patterns, as the difference between peak and low months is dramatic.
Wind
Ko Samui is relatively calm, with an average annual wind speed of 5km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is August, averaging 6km/h, though still comfortable for most outdoor activities. The calmest conditions occur in May, with average winds dropping to 4km/h, making it an ideal period for wind-sensitive activities. There is moderate seasonal variation in wind speed, with a 2km/h gap between the calmest and windiest months.
Seasons
93 days until Autumn
It is currently summer in Ko Samui, which began on June 21, 2026. Ko Samui sits near the equator, so the traditional four-season cycle is less pronounced — temperatures remain relatively stable year-round. The warmest period peaks in May at around 30°C, while the coldest stretch bottoms out in December near 26°C. Autumn is next, beginning on September 23, 2026 — 93 days from now.
Spring
Temperatures range from 27 to 30°C. Precipitation is moderate at around 287mm for the season, averaging 96mm per month. Winds are generally light, averaging 4km/h. An umbrella or waterproof jacket is advisable as spring showers are frequent.
Summer
Temperatures range from 27 to 30°C. Rainfall is heavy, totalling around 302mm across the season with a monthly average of 101mm. Winds are generally light, averaging 5km/h. Light, breathable clothing is ideal — perfect conditions for outdoor activities.
Autumn
Temperatures range from 26 to 28°C. Rainfall is heavy, totalling around 669mm across the season with a monthly average of 223mm. Winds are generally light, averaging 4km/h. A waterproof jacket and sturdy footwear are recommended as rain becomes more frequent.
Winter
Temperatures range from 26 to 28°C. Rainfall is heavy, totalling around 464mm across the season with a monthly average of 155mm. Winds are generally light, averaging 5km/h. A light jacket or sweater is usually sufficient, though cooler evenings may call for an extra layer.
Monthly Climate Data
The table below shows monthly climate averages for Ko Samui based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.
