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). There are different seasons depending on the region. Temperature ranges from 23°C to 32°C all year around in both Andaman Sea & Gulf of Thailand, but there are important differences in precipitation. Comparing the weather in Koh Samui with the weather in 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 temperature all year around. 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, as well known as Cool, Hot and Wet.
Early January to Mid April
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. Be prepared to enjoy some of the most amazing sunsets you have ever seen. During these months, Koh Samui can get busy for Saint Valentine, Chinese New Year and Songkran so make sure you book in advance to avoid disappointment.
Mid April to end of September
The hot season is long in Koh Samui. The temperature is warm and humid with occasional storms. It is a great time to visit the island with less tourists than the cool season. September is one of our favorite months to relax. Short showers are welcomed to refresh the atmosphere. This time of the year is not as busy as the peak season so you may get good offers specially during September.
October to Early January
In Koh Samui, you won’t need more than your shorts and flip flops to walk around anytime. Good temperatures all year around means you can enjoy Koh Samui during the rainy season if you want to explore the island and relax without too many tourists around, don’t expect to get a nice skin tan though… Note- Early December & Christmas are quite popular, make sure you book in advance!
Best Time to Visit Koh Samui
Ask yourself what is more important to you between, heat, sunshine, rain, prices, holiday plan and how busy you prefer the island to be.
November is the wettest month of the year with rainfall most days. Some holiday makers, looking to relax enjoying activities like yoga retreats or SPA indulgences. Holiday makers chose to visit the island this month because is quieter and prices are lower. However, if you are coming from a country with cold or rainy conditions, looking for sun and water sports, probably is better to skip the rainy season and visit from January to September.
The best time to visit the island varies depending on your own preferences. If you are seeking for sunshine and a beach holiday aim for the hot and dry seasons. If you are into kite surfing, there are some spots with decent wind speed in Nathon, where you can surf during the quieter moths. If you prefer to enjoy a SPA retreat, any time is good. If you are tight on budget, perhaps the low season can be more appealing to your needs. Best thing about the island is you have so many options to chose from, regardless if you are looking for a beach day, adventure, water sports, visiting, 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 little rain but the daytime temperature is mostly pleasant. The average Koh Samui weather is warm with tropical humidity. Sometimes rainy days are a blessing when is too hot!
What to Expect
Any time is great to visit the island aside November, the rainiest month of the year. But as Thais say, in Thailand you get 3 season: “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 on the peak season.
Climate can be difficult to predict. Clouds move fast and there are micro climates on 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.
During floods, be aware of health risks and hazards. We have seen pictures in social media during the rainy season, showing tourist playing with inflatable toys in the floods; Please use your common sense. Floods carry sewage waters, bacteria and debris. Avoid skin contact with flood waters. You can get cut or develop a serious infection. As well, beware of mosquitos after the rain!