Weather in Koh Samui

Most of the year, visitors to Samui and the surrounding coastal areas can expect pleasant weather. During the high season (December to February), temperatures on Samui usually hover around 30°C (86°F). The seas during this time of year are tranquil, with clear waters and gentle breezes. Although there might be occasional tropical downpours in December, this period is still considered the optimal time to visit as the weather is cooler compared to later months.

From March to June, the weather on Samui can become quite hot, reaching temperatures up to 40°C (104°F). Rainfall is minimal during these months, which can result in water shortages. The slower pace of life during this period helps cope with the heat. The sea remains calm, and low tides can create shallow waters along the island’s beaches. Wind patterns pick up again in May, making it a popular time for off-season visits. In the late afternoon, significant thunderstorms occasionally form offshore and move toward the island.

From July to September, the weather on Samui becomes slightly cooler, accompanied by a mini-monsoon season that brings intermittent storms and periods of heavy rainfall. Despite this, these months remain popular among visitors, as there is still a good amount of sunshine to enjoy during their vacation.

October and November bring more rain compared to other months, although it doesn’t typically rain every day. Unlike many other regions in the country, Koh Samui lacks a prolonged or predictable rainy season. Even during the wettest periods, which include November, it’s rare to experience more than two or three consecutive days without sunlight. Although November is often considered part of the monsoon season, Samui’s weather during this time remains unpredictable, and the sea conditions can be unusually rough.

Regardless of the season you choose to visit Koh Samui, one thing you won’t frequently experience as a tourist is a cold weather, as the island enjoys a warm and tropical climate.

Koh Samui Weather By Month

Weather in Koh Samui in January

After the New Year has hit, the island’s weather is quite temperamental. The northeast monsoon season has departed and it starts getting warmer, but still with a chance of rain. If it does decide to shower, it should only be a short burst. This is the most popular season and hotels can be full and premium priced.

Weather in Koh Samui in February

Generally, this time of year sees a dramatic reduction in winds when windsurfing and kite-surfing (on the east of the island) water sports come to a standstill. Temperatures are hitting the mid-30s (°C) by day and there is not much let-up at night. The weather in Samui remains dry in February; thus, this is a popular time to visit.

Weather in Koh Samui in March

Although the weather is warm in Samui in March, this is an ideal time to take a trip from Koh Samui to Koh Tao if boats are not your favorite mode of transport. The seas are generally tranquil and it makes ideal weather to scuba dive and snorkel. However, the sun is reaching its daytime peak and it can become unbearable in the midday heat.

Weather in Koh Samui in April

April is traditionally the hottest month of the year in Samui. The Songkran water festival takes place in mid-April and it makes for the best way to cool down. If you see rain, you will be blessed as it does not happen often at this time. Expect temperatures in the 40s and without the benefit of sea breezes.

Weather in Koh Samui in May

The season quietens down on Samui from May onwards; the weather remains hot, while rains are yet to arrive. You can get good discounts on hotel rooms at this time, while also enjoying plenty of sunshine, but be careful of sunburn!

Weather in Koh Samui in June

From the middle of the year in June, the weather will start its long transition into the rainy season. The rainfall average will remain steady for the next four months and temperatures will decline. This doesn’t mean it gets cold – far from it – more it cools off a little and becomes sticky and humid due to cloud cover.

Weather in Koh Samui in July

The start of the European school summer holidays brings unusual weather to Samui and the surrounding islands in July. Hotels and guesthouses start to get busier and the weather can be volatile, with crashing waves on a rainy day to sunshine and still air the next, so it really can be hit and miss.

Weather in Koh Samui in August

As the schools have finished, the influx of backpackers heading to the island rises quite dramatically. Many head over to Koh Pha Ngan to relax, but there’s no real need to book in advance and prices are ‘low season’ rates. As in July, the daily weather can be quite random – hot and sunny one day, rainy and windy the next.

Weather in Koh Samui in September

Heading out of the summer season in September can be the start of the infamous Samui rainy season. Temperatures do not fluctuate much throughout the year, although even slightly higher ground at night can be cooler. September is one of the quietest months on the island, yet can still be pleasant.

Weather in Koh Samui in October

The rainy season has touched down officially, so remember your umbrella as you will likely need it. There is still time to sunbathe, but if you are there for two weeks do not plan on a deep tan.

Weather in Koh Samui in November

This is possibly the only time of year you may want to avoid because of the weather. November can see flash floods around the island and although the local council has worked on installing new flood defenses, you may well see locals canoe down the street outside the bar you are stuck in.

Weather in Koh Samui in December

December is the most popular month to visit Samui. The weather is agreeable and cooler and there is just a slight chance of afternoon showers. Expect crowds and high-season hotel prices.