May in Ko Samui averages a daily high of 32.9°C with nights around 25.6°C. Expect roughly 13.4 wet days totalling 122.4mm. Demanding conditions — pack for it and plan indoor options.
Across the year, the best time to visit Ko Samui is January–April.
Based on KO SAMUI, TH (14.7km), 1995–2024. 25 years of May data.