Koh Samui is one of Thailand’s most popular tropical island holiday destinations which lies in the Gulf of Thailand, part of the South China Sea. The island is renowned for its endless stretches of white sands, coconut tree-covered hillsides and idyllic weather throughout most of the year. But when are the best times to visit Koh Samui and are there any times that should be avoided to ensure the sun shines throughout your stay?
The weather on Koh Samui is dry, humid and hot throughout the year though it is affected by both the Southeast Monsoon and the Northwest Monsoon systems. The SE monsoon causes storms to sweep in from Indonesia and The Philippines towards Thailand and Malaysia during the months of October, November, and December. The NW monsoon moves in from India during the months of June, July and the start of August through Koh Samui isn’t badly affected by this system as the Thai mainland protects the island from much of its effects.
During the months of June, July and the start of August, the NW monsoon lightly affects Samui with heavy showers that generally last about 30 minutes, mostly confined to late afternoon or early evening. The more powerful SE monsoon system can cause powerful, tropical storms to sweep into the island which can last for up to one week with torrential rainfall and high winds. During this rainy season, Samui can be hit by several storms though it is important to note that the weather usually remains dry with hot and sunny spells between storms and it is not a time of constant rainfall.
When a bad storm does hit Koh Samui and its surrounding islands, the effects can be frightening. Large torrents of water run down from the island’s central, mountainous region causing flash flooding to hit the coastal towns, closing roads and businesses and often causing long power cuts. The tourist center of Chaweng is usually the first area of the island to be affected by the rainfall as Chaweng Lake overflows and floods the town with water up to one meter or more in-depth. The tourist areas of Bophut, Maenam, Lamai, and Cheong Mon are also prone to flash floods though they are not as intense as the flooding in Chaweng. Recent improvements in drainage do mean however that the floods subside reasonably quickly when the rainfall finally stops.
Statistically, November is the wettest month with 500 mm of rainfall followed by October and December when about 200mm of rainfall. Throughout the rest of the year, rainfall measurements are between 50 and 150mm with February being the driest month.
Koh Samui’s average temperatures throughout the year are quite constant, between 29 and 32 degrees Celsius, though during the hottest months of February, March, April and May highest temperatures can reach as high as 38 Celsius. Lowest temperatures during the SE monsoon can reach a low as 18 Celsius with the highest temperatures of about 32 Celsius.
For guaranteed sunshine, without a doubt, the best time to visit Koh Samui is during the hot season from February to May when the possibility of rainstorms is very low and temperatures are at their highest. The months of June to August have a higher chance of heavy showers in late afternoon or evening but during the day the weather is sunny and hot, though more pleasant than the sometimes uncomfortable heat of February to May.