"Small craft advisory" is a indicator that a speedboat tour will be very bumpy. We do not operate any powerboat trip in this case. Koh Samui Seasons: Average Temperatures, Rain and Wind on Koh Samui Koh Samui has three seasons. February to May is the hot and dry season with peak daytime temperatures up to 40 degrees Celsius and little rain, except for short, but heavy cloudbursts. This weather is just perfect to spend some days on a boat, although winds - usually blowing from the east can be a bit sluggish. The typical weather from June to September brings more tropical rain showers, a short and welcome breather from the heat of the day. Daytime temperatures are in the high twenties while the humidity is rather low, at least compared to other places in Thailand at this time of the year. The sea is generally calm and smooth, very good conditions for boaters if you are not too bothered by the frequent late afternoon showers. Note that Koh Samui is located off the east coast of Thailand, and therefore shielded from the south-eastern monsoon hammering Thailand's Andaman coast during this period. Koh Samui's monsoon season starts in October with sometimes torrential rain falls, winds around 20knots and waves up to 2 meters from the east. This weather is caused by the north-east monsoon coming down from China. Luckily the so called rain season here occurs in periods of 3-4 wet days followed by a few friendly ones, so it is still possible to find a good window for a relaxing sailing session. Also November can be rather wet. Temperatures drop to the low twenties at night - which is quite cold by local standards. The heavy rain and flooding usually comes to an end in early December. The wind still blows from the east, bringing up some surf to the east coast. Fortunately the the bays of Bophud, Maenam, Lipa Noi and Taling Ngam are somewhat sheltered from the elements at that time.