Gulf of Thailand Weather
Andaman Sea Weather
The weather in the Gulf of Thailand (east coast of Thailand: Koh Samui, Koh Phangan and Koh Tao) is quite different from the weather in the Andaman Sea (west coast of Thailand: Phuket, Krabi and Koh Lanta). Although the temperature ranges from 23 °C to 32 °C all year around in both the Andaman Sea and the Gulf of Thailand, there are important differences in precipitation. The best time to visit Phuket and Krabi, is not necessarily the best time to visit Koh Samui. Comparing the weather in Koh Samui and Phuket, average rainfall shows November is the rainiest month in Koh Samui; September in Phuket.
Check the graphs below comparing rainfall in different popular destinations in Thailand. The data is provided by the Thai Meteorological Department (2018).
Koh Samui Weather by Season
Koh Samui is a tropical island with pleasant temperatures all year round. Rain can be unpredictable and, at times, torrential. There are 3 seasons in Koh Samui as in the rest of Thailand: Dry, Hot and Rainy, also known as Cool, Hot and Wet.
Mid-December to February
The dry season is for many the best time to visit Koh Samui. Therefore, is the high season. The weather is usually pleasant, not too hot and without much rain or none at all.
Tip: During these months, Koh Samui can get very busy, especially for Christmas, St Valentine’s and Chinese New Year, so make sure you book in advance to avoid disappointment.
March to August
The hot season in Koh Samui is long. The temperature is hot and very humid with occasional storms. The hottest months are April and May, with temperatures hitting 30 degrees plus.
Tip: At this time of the year, you can enjoy some of the most amazing sunsets you have ever seen. If the heat doesn’t bother you, this is a good time to visit the island with fewer tourists than in the cool season. However, the months of April, July and August can still be pretty busy, because of Songkran Festival (April) and the school holidays (July and August).
September to Mid-December
In Koh Samui, at any time of the year, you won’t need more than your shorts and flip-flops to walk around. Good temperatures all year around means you can enjoy the island even during the rainy season. If you hate crowds, and you want to explore the island and relax without too many tourists, this is the best time to visit, but don’t expect a nice suntan though…
A little tip: September can be one of the best months to visit, if peace and quiet is what you’re after. Still very little rain and the chance of getting some excellent offers on accommodation.
Best Time to Visit Koh Samui
The best time to visit Koh Samui is different for everyone, and it depends on what is more important to you: warm weather and plenty of sunshine, no rain, great prices and offers, avoiding crowds.
November is the wettest month of the year with rainfall on most days. Some holidaymakers, looking to relax, choose this time of year to come and enjoy activities like yoga classes, Muay Thai classes, wellness and fitness retreats. You can take advantage of the quiet beaches and hotel’s lower rates. However, if you are coming from a country with cold or rainy conditions, looking for sun and water sports, probably better to skip the rainy season and visit from mid-December to August.
As we mentioned above, the best time to visit the island depends on your own preferences. If a beach holiday is what you’re after, aim for the hot and dry seasons. If you are into kite surfing, there are some good spots with decent wind speed in Nathon, where you can surf during the quieter months. If you prefer to enjoy a retreat, any time is good. If you are tight on budget, perhaps the low season can be more appealing to your needs.
The best thing about Koh Samui is that you have so many options to choose from, whether you are looking for a beach day, adventure, water sports, exploring, eating or relaxing.
At anytime during the year, including the monsoon season, the average temperature ranges from 28 °C to 30 °C. At night, it might be cooler if there is wind or a little rain, but the daytime temperature is mostly pleasant. Sometimes, in the hot season, rainy days are a blessing!
What to Expect
Any time is great to visit the island, apart from November, the rainiest month of the year. But as Thais say, in Thailand you get 3 seasons: “Hot – Hotter – Hottest”. Most of the year you should expect sunny days, calm seas, nice water temperature, high humidity, and the occasional tropical thunderstorm. February is usually the driest month right in the peak season.
The weather can be difficult to predict. Clouds move fast and there are microclimates in different locations on the island. Even popular weather forecast sites don’t get it right. You may see a forecast showing storms every day, but then, not see a single rain shower in the whole week. Go with the historical averages on this page to get an idea and check the forecast for guidance.