Weather in Koh Samui in December

How December compares

December is the 12th warmest month of the year in Koh Samui and ranks 22nd of 134 destinations we compare for December - see where else is hot in December. Within Thailand it is 5th of 6 (Thailand in December). Against London's average high of 7.7°C in December, Koh Samui is 19.8°C warmer by day and 22.8°C warmer at night.

Daytime and night-time in December

The typical December day in Koh Samui peaks at 27.5°C, but that is an average: the warmest 10% of days reach 28.5°C or more. About 100% of days top 25°C. Nights average 25.5°C; one night in ten drops to 24.2°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest December day here reached 29.7°C (2019-12-16) and the coldest night 22.3°C (1999-12-25).

Rain in December

Wet (more than 8 rainy days): about 14 days with 1 mm or more, 144 mm in total. Year to year it varies a lot - the wettest December was 2016 with 519 mm, the driest 2004 with 10 mm. Humidity averages 78%.

Sea temperature in December

The sea averages 28.0°C - warm enough to swim (22°c+). Depending on the year it ranges from 27.1°C to 28.7°C. For the warmest sea here, come in May (30.5°C).

Sunshine and daylight

Around 3.9 hours of sunshine a day (estimated from cloud cover), 11.4 hours of daylight: the sun rises about 06:28 and sets about 18:02 local time in mid-December. Average cloud cover is 66%.

Is December a good time to visit Koh Samui?

It is a reasonable choice: hot days but expect showers. 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.

Warm enough to swim, warm after dark

December is Koh Samui's coolest month, but that is relative: it still feels hot rather than mild. Average night lows of 25.5°C mean you should not expect a crisp evening after a warm afternoon. With humidity at 78%, loose, breathable clothing makes more sense than heavy layers, and air conditioning is worth prioritising when choosing accommodation. Plan active outings for when you feel most comfortable and leave room for shade breaks at midday. The sea is suitable for swimming on temperature alone, so getting into the water should not require much resolve. That warmth does not, however, tell you about waves or local swimming conditions.

Plan around rain, not guaranteed blue skies

The main compromise is the weather between swims. December is wet, and about 3.9 hours of sunshine within 11.4 hours of daylight means a bright day should not be taken for granted. Rainy days do not necessarily mean continuous rain, but you should not assume showers will be brief or conveniently timed either. Keep outdoor plans flexible, pack a light waterproof and have something you are happy doing under cover. This month suits travellers who can enjoy the warmth even when the sky is grey. If your holiday depends on long stretches of sunshine, the rain risk makes December a less comfortable choice.