The best time to visit Koh Samui is from December to March. During this period, there’s less rainfall, the weather is hot but less humid, and the sea is calm and clear.
The island’s climate is tropical with essentially three seasons: hot and less humid; hot and increasingly humid, with plenty of sunshine; and then a short but intense rainy season in October and November as the northeast monsoon arrives.
Outside the monsoon season, you can expect mainly blue skies, a blissfully warm sea, and as is typical of the tropics, the occasional short, sharp shower.
Visiting Koh Samui by Season
Summer
Beach in Koh Samui
June, July, and August are hot and humid, with partly cloudy skies and occasional sharp bursts of rain that clear the air. This is the shoulder season in Koh Samui because of the heat, with average daily temperatures of around 84.2°F (29°C). But summer can be a great time to go to Koh Samui for anybody who doesn’t mind the humidity.
Summer is a popular time among families who visit during the Northern Hemisphere school vacation. Thais also favor Koh Samui in the summer months, when much of the rest of the country is in the grip of the monsoon.
Fall
As fall progresses, the northeast monsoon wind intensifies, traveling across the Gulf of Thailand and picking up water. As such, October and November are the wettest months of the year. October receives on average 11.6 inches (295mm), while in November, the average is an impressive 17.5 inches (445mm).
This isn’t the time to come for sitting on the beach, and the sea can be choppy. During the monsoon season, the island is quiet. By December, the weather is more settled, although there will still be rain showers in between sunny periods.
Winter
Chaweng Beach
January and February is the best time to go to Koh Samui, with dry, settled weather and long, sunny days. Temperatures are marginally cooler than other months, with January basking in an average of 79.9°F (26.6°C), perfect for enjoying the white sand beaches and exploring the island. February has the lowest rainfall of the year, too, with just 2.6 inches (65mm) falling.
Spring
March, April, and May are still good months to visit Koh Samui, although the heat and humidity are becoming more intense; in May, you can expect average temperatures of 84.7°F (29.3°C).
Rainfall increases, with an average of 5.3 inches (135mm) by June, although this is still low relative to the big monsoon rains that come in fall. Visit in May and you can expect a mixture of sunshine and clouds, with evening showers clearing the air.
When Is Rainy Season?
Despite the rain, the Gulf of Thailand is sheltered, and tropical cyclones are unusual in Koh Samui. This Asian island is also different from much of Thailand in that it’s not affected by the southwest monsoon that brings rain to places like Phuket in the summer months. Instead, Koh Samui has its own rainy season in October and November, with November being the wettest month.
When Is High Season?
Beach in Koh Samui
December to March is peak season in Koh Samui, with dry, settled weather and more visitors. While Thailand is a Buddhist country, Christmas and New Year’s are nonetheless busy times as visitors come from colder climates in search of a vacation in the sun.
The rest of Thailand also enjoys fine weather at this time of year, making December to February ideal for a multi-destination vacation.
When Is Shoulder Season?
April to August could be considered the shoulder season in Koh Samui. The weather is generally fine but temperatures are high. This is a time for enjoying watersports and swimming in the bath-like sea, and taking life slowly, as the humidity can be energy-sapping.
Come in April and you’ll experience Songkran, Thailand’s famous water festival which takes place as Thai New Year is celebrated, between April 13 and 15. Thais “wash away” the old year in what’s essentially one big water fight.
When Is Low Season?
October and November is the quietest time in Koh Samui as it’s when rainfall is highest. If you do visit during this period, the weather will still be hot and you can swim in the sea and explore the island—but there will be heavy showers. The interior is at its most lush and green during the low season.
Wat Plai Laem
Discover beautiful Koh Samui for yourself on one of Celebrity’s cruises to Thailand. Browse our cruises to Koh Samui and plan your dream tropical vacation.
