Koh Samui has a tropical monsoon climate, classified as Am in the Köppen system. The warmest month is April with an average high of 27°C, while the coldest month is January with lows dropping to 23°C. The annual temperature range of 4°C indicates a relatively stable climate year-round.
The driest month is February with only 6 rain days and 36mm of precipitation. For travellers, February through to the following month typically offers the best balance of warm temperatures and dry conditions. Average humidity ranges from 82% to 82% throughout the year.
Best Time to Visit Koh Samui
Based on temperature and rainfall data, the best months to visit Koh Samui are February, January, March. These months offer the most comfortable temperatures with relatively low rainfall, ideal for sightseeing and outdoor activities.
In April, Koh Samui experiences average highs of 27°C (81°F) and lows of 24°C (75°F). Expect around 12 rainy days and 11 hours of sunshine per day, with humidity averaging 82%. The 3°C gap between daytime and overnight temperatures is worth planning around: light layers work for most visitors during the day, but an overshirt or cardigan handles the cooler evenings. UV index averages 6, so sun protection is advisable on clear days.
Koh Samui typically sees 12 rainy days in April, with total precipitation of around 96mm. Rain is moderate and manageable. Showers tend to pass quickly, and a light rain layer or foldable umbrella is sufficient protection for most days. For context, the driest month in Koh Samui typically sees 4-6 fewer rain days than April.
Pack light layers, a light jacket for evenings, comfortable walking shoes, and sunscreen for Koh Samui in April. Daytime temperatures of 27°C are pleasant, but the evening drop to 24°C means a jacket is essential if you plan to be out after dark. With 12 rainy days, bring a compact umbrella or waterproof jacket for unexpected showers. Comfortable walking shoes are a priority given the amount of ground most visitors cover.
April is a reasonable time to visit Koh Samui. Expect 12 rainy days, so pack a light rain layer for flexibility. Average temperatures of 27°C make outdoor exploration comfortable during the dry periods. With 11 daily sunshine hours, there are reliable windows of good weather to plan outdoor activities around, even if the month is not the driest on the calendar.
The average high temperature in Koh Samui in April is 27°C (81°F), and the average low is 24°C (75°F). The mean daily temperature is approximately 26°C (78°F). The day-to-night range of 3°C is narrow, typical of coastal or maritime cities. These are 30-year climate normals based on the 1991 to 2020 reference period; individual years will vary, particularly in transitional months like spring and autumn.
The best month to visit Koh Samui is generally January. January offers the most sunshine at 11 hours per day and only 11 rainy days. Average temperatures reach 25°C, making it comfortable for sightseeing, outdoor dining, and exploring the city. If your travel dates are flexible, planning your trip around January gives you the best chance of dry, bright weather.
April is shoulder or low season in Koh Samui, meaning fewer tourists and generally lower prices than peak months. With 11 sunshine hours and 12 rainy days, the weather is less of a draw for mass tourism. This is an advantage for travellers who prefer a quieter, more relaxed experience with shorter queues and easier accommodation availability.
In April, Koh Samui suits a range of activities thanks to mild temperatures around 27°C. Mix of indoor and outdoor activities works well given the moderate chance of rain. Top options include exploring historic neighbourhoods, visiting museums and galleries, local food markets, and day trips to surrounding areas. With 11 hours of sunshine, parks and waterfront walks are particularly enjoyable.