Koh Samui weather can typically be summed up in one word: hot. Average temperatures range from 26 to 30 degrees year round, but when it comes to planning your trip you’ll want to consider other factors too.
The island has a tropical climate, which means that the high temperatures bring a level of humidity with them – and while for much of the year you can expect dry sunny days, there’s inevitably a rainy season. The Koh Samui monsoon typically peaks in November, and while the intensity varies year on year, the heaviest rainfall doesn’t stick around for too long.
January is typically Koh Samui’s coolest month, but you’re unlikely to feel chilly – the average temperature is still a fine 26 degrees. Average sea temperatures are also at a low, but since those also clock in at around 26 degrees, there’s no need to stay out of the water.
Temperatures begin to climb in February, with an average high of around 27. Average rainfall drops to its lowest for the year, and typically the island will only see occasional light showers on around 4 days during this month.
March is when Koh Samui’s temperature really begins to soar. The average temperature is 29 degrees, but expect it to be hotter than this a lot of the time. This is another month when rainfall will be at the lower end of the spectrum, making this the ideal time for lounging on the beach.
In April, the Koh Samui weather is back at its hottest. During the daytime, temperatures regularly reach above 32 degrees, but the humidity usually drops off, making for a more comfortable heat. The Songkran festival falls in the middle of April, and it’s no coincidence that one of the most popular traditions is the all day waterfight – if you get the chance to take part, do.
The high temperatures continue through May, and it’s a great time of year to visit if you’re planning to enjoy watersports. The average sea temperature at this time of year is a welcoming 28 degrees – warm enough to be inviting, but still refreshingly cool compared to the temperature on land. The build up of tropical temperatures can lead to a little more rain than April, but showers are usually over quickly.
In June and July, weather in Koh Samui settles at a balmy average of 29 degrees. Highs can still rise to around 32, but there are also some cooler days. Many find the temperature from June to August more comfortable than the soaring heights of April and May.
While June, July and August in Koh Samui can bring showers, these are usually limited to the late afternoons. After a scorcher of a sunny day, a short burst of rainfall cools the humidity in the air, cooling everyone off in time to get dressed up for the evening ahead.
By September, weather in Koh Samui is starting to cool off a little as we near the rainy season. However, at around 28 degrees it’s still reliably warm and dry enough to spend much of the time basking in the sun. Those late afternoon showers will still be around, but nothing drastic.
The big change comes in October. Average temperatures drop a degree or so back to 27, and that’s not the only change in the weather. Koh Samui’s monsoon season hits towards the end of the month, lasts throughout November and trails off into December. While flooding used to be an issue, the island now has proper drainage systems, but the rainfall can still be pretty spectacular.
If you’re thinking of visiting Koh Samui during October, November or early December, be aware that at times, the monsoon conditions might curtail your plans to hit the beach. However, there are often sunny days during monsoon in Koh Samui – 14 day weather forecasts can be easily checked online in advance to make sure you catch the best of the sunshine.
When planning your trip, it’s a good idea to consider the type of weather that’ll best suit you. Looking to spend a lot of time on the beach? Consider February, when rainfall is low and temperatures aren’t too hot to laze in the sun. September is considered low season as rainfall begins to increase, but if you’re planning on being out and about exploring, it’s a great time to pick up a bargain.
One final tip: if visiting during the wetter months, check the Koh Samui weather forecast in the evening, to plan ahead for the next day. And don’t forget the suntan lotion!