Weather in Koh Samui in March

How March compares

March is the 6th warmest month of the year in Koh Samui and ranks 17th of 134 destinations we compare for March - see where else is hot in March. Within Thailand it is 6th of 6 (Thailand in March). Against London's average high of 10.5°C in March, Koh Samui is 18.7°C warmer by day and 23.3°C warmer at night.

Daytime and night-time in March

The typical March day in Koh Samui peaks at 29.2°C, but that is an average: the warmest 10% of days reach 30.6°C or more. About 100% of days top 25°C and 1 in 4 pass 30°C. Nights average 26.6°C; one night in ten drops to 25.2°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest March day here reached 33.6°C (2020-03-09) and the coldest night 22.7°C (2019-03-09).

Rain in March

Wet (more than 8 rainy days): about 9 days with 1 mm or more, 87 mm in total. Year to year it varies a lot - the wettest March was 2011 with 942 mm, the driest 1992 with 1 mm. Humidity averages 77%, which makes the heat feel heavier than the thermometer suggests.

Sea temperature in March

The sea averages 29.2°C - warm enough to swim (22°c+). Depending on the year it ranges from 28.8°C to 29.7°C. For the warmest sea here, come in May (30.5°C).

Sunshine and daylight

Around 6.2 hours of sunshine a day (estimated from cloud cover), 11.9 hours of daylight: the sun rises about 06:27 and sets about 18:31 local time in mid-March. Average cloud cover is 48%.

Is March a good time to visit Koh Samui?

Yes - it is one of the better months: hot days, manageable rain. The best months for Koh Samui on our scoring are February, March, January; months averaging 25°C or more: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec.

Expect heat that lasts into the evening

Pack for consistently hot conditions rather than a mix of warm and cool days. Every March day reaches 25°C in the figures, while 23% reach 30°C, so heat is part of the holiday rather than an occasional bonus. Humidity averages 77%, which can make walking around feel more tiring than the temperature alone suggests. Loose, breathable clothes are the practical choice, with active plans better kept away from midday. Evenings remain warm enough for light clothing, and air conditioning is worth prioritising if you struggle to sleep in the heat. March is not Koh Samui's hottest month, but it is still firmly hot.

Plan around rain, not just sunshine

The catch is that a favourable month here can still be wet. About 9 days have measurable rain, so avoid building the whole trip around outdoor plans that cannot move. The monthly figures do not tell you when rain will arrive or how long each spell will last; keep some flexibility rather than assuming it will only rain briefly. Sunshine averages about 6.2 hours within 11.9 hours of daylight, so daylight does not mean constant clear skies. This suits travellers happy to mix swimming and time outside with breaks under cover. If uninterrupted sunshine is your main requirement, March still carries a risk of disappointment.