Weather in Koh Samui in July

How July compares

July is the 4th warmest month of the year in Koh Samui and ranks 46th of 134 destinations we compare for July - see where else is hot in July. Within Thailand it is 3rd of 6 (Thailand in July). Against London's average high of 21.8°C in July, Koh Samui is 7.8°C warmer by day and 13.3°C warmer at night.

Daytime and night-time in July

The typical July day in Koh Samui peaks at 29.6°C, but that is an average: the warmest 10% of days reach 30.9°C or more. About 100% of days top 25°C and 1 in 3 pass 30°C. Nights average 26.8°C; one night in ten drops to 26.0°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest July day here reached 33.3°C (2019-07-09) and the coldest night 24.5°C (2003-07-06).

Rain in July

Wet (more than 8 rainy days): about 19 days with 1 mm or more, 88 mm in total. Year to year it varies a lot - the wettest July was 2016 with 166 mm, the driest 2014 with 33 mm. Humidity averages 77%, which makes the heat feel heavier than the thermometer suggests.

Sea temperature in July

The sea averages 29.4°C - warm enough to swim (22°c+). Depending on the year it ranges from 28.9°C to 29.8°C. For the warmest sea here, come in May (30.5°C).

Sunshine and daylight

Around 1.7 hours of sunshine a day (estimated from cloud cover), 12.5 hours of daylight: the sun rises about 06:07 and sets about 18:45 local time in mid-July. Average cloud cover is 87%.

Is July 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.

Hot days, with little relief at night

The heat is fairly consistent rather than confined to occasional hot spells: every July day reaches 25°C in the averages, while 32% reach 30°C. With humidity at 77%, light, loose clothing is a more practical choice than anything heavy or close-fitting. Keep strenuous plans away from midday and leave room for breaks somewhere cool. Nights remain warm enough that a room with air conditioning is worth prioritising if you struggle to sleep in heat. This suits travellers who enjoy sustained warmth, but less so anyone hoping for pleasantly cool evenings after a hot day. Pack for warmth throughout, not a marked evening temperature drop.

Plan around cloud and rain, not guaranteed sun

July's catch is the limited sunshine, not a shortage of daylight. There are about 1.7 hours of sunshine within 12.5 hours of daylight, so warm conditions should not be mistaken for clear skies. Rain is frequent enough to make rigid outdoor plans frustrating, although a rainy day does not necessarily mean rain throughout the day. Keep your schedule flexible, carry a light waterproof and protect anything that needs to stay dry. The figures do not establish a dependable time of day for showers, so avoid assuming mornings or afternoons will always be clear. July is easier to enjoy if sunshine is a bonus rather than the whole point.

Warm swimming water is the strongest draw

At 29.4°C, the sea is comfortably warm for swimming, making water temperature a clear reason to consider July. It should not feel like a cold plunge, though it may offer less cooling relief from the air than you might expect. Warm water alone does not establish safe swimming conditions, so check conditions locally before entering. For a long-haul holiday, the decision comes down to priorities: July makes sense if you value warm water and can adapt your days around rain and cloud. If your main aim is dependable sunbathing weather, the low sunshine average is a substantial drawback, despite the inviting sea temperature.