Weather in Koh Samui in January

How January compares

January is the 11th warmest month of the year in Koh Samui and ranks 22nd of 134 destinations we compare for January - see where else is hot in January. Within Thailand it is 6th of 6 (Thailand in January). Against London's average high of 7.4°C in January, Koh Samui is 20.1°C warmer by day and 23.2°C warmer at night.

Daytime and night-time in January

The typical January 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 and 1 in 67 pass 30°C. Nights average 25.4°C; one night in ten drops to 24.2°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest January day here reached 30.6°C (2020-01-17) and the coldest night 21.7°C (2017-01-29).

Rain in January

Wet (more than 8 rainy days): about 10 days with 1 mm or more, 78 mm in total. Year to year it varies a lot - the wettest January was 2017 with 510 mm, the driest 1997 with 8 mm. Humidity averages 77%.

Sea temperature in January

The sea averages 27.7°C - warm enough to swim (22°c+). Depending on the year it ranges from 27.0°C to 28.7°C. For the warmest sea here, come in May (30.5°C).

Sunshine and daylight

Around 5.1 hours of sunshine a day (estimated from cloud cover), 11.5 hours of daylight: the sun rises about 06:41 and sets about 18:18 local time in mid-January. Average cloud cover is 55%.

Is January 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 days, with little cooling after dark

January is among Koh Samui's cooler months, but that is relative: it still feels hot, especially with humidity at 77%. Nights average 25.4°C, so evenings offer little relief and light, breathable clothing makes more sense than warm layers. If you dislike very high temperatures, January has an advantage: only 2% of days reach 30°C. That does not make midday cool, so keep your more active plans flexible and allow time in the shade. For packing, prioritise loose clothes and consider how comfortable you sleep in warm conditions when choosing your room. This suits travellers seeking steady warmth rather than those hoping for fresh evenings.

Good swimming conditions, but plan around rain

The sea is warm enough for swimming, making January a reasonable choice if time in the water matters more to you than uninterrupted sunshine. Sunshine averages about 5.1 hours within 11.5 hours of daylight, so expect a mixture of sun and cloud rather than clear skies throughout. Rain is a real planning consideration, not something to dismiss, although a rainy day does not necessarily mean a whole day indoors. Carry lightweight rain protection and keep plans movable. The warm sea temperature tells you about comfort, not wave conditions or swimming safety, so check conditions locally before entering the water. January suits a flexible beach holiday better than a tightly scheduled outdoor trip.