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The Weather and Climate of Koh Samui


The weather and climate of Koh Samui are tropical and warm all year long, yet, due to the monsoon of Southeast Asia; the island also witnesses a long rainy season, a short drier season, and a hot season.

Rainy Season

From May to the middle of January, in which the rainiest would be November and October. During this time of the year; the weather gets unpredictable and sea waves may get higher and tougher.

Dry Season

The dry season would be from mid-January to April, however, we can say that Samui has only one dry month, as the driest is always the month of February.

It is considered as the hotels’ peak season, as the temperature is usually cooler, the sea is calmer, and the rain is few. Yet, there is always the possibility of some showers that may occur at any time.

Hot Season

This is the perfect time for hot sunny weather lovers, as it’s when the temperature hits 30 degrees plus, and this would be between March and May.

There is a sudden increase in precipitation around late April-early May.

Starting May, strong daytime sunshine is expected up until September, which continues until the afternoon thunderstorms kick in.

Details kind of person? Here is some detailed weather information.


The amount of rainfall adds up to nearly 1,900 millimeters each year. And one of the magnificent results of this tropical rainy weather is that it allows the forest to extend into the island’s interior; resulting in the remarkable greenery views we can spot anywhere on the island.

The rainy season mainly beholds two distinguished peak periods; the first one would be in early May, afterward, rainfall continues to pour within a normal rate. Then follows short-lived downpours or showers from June to September.

The highest peak period occurs between October and December, especially in November when the rainfall is relentless.

And this mainly occurs because of Koh Samui’s location; as the island is situated a small distance from Peninsular Thailand. And during the end of the year; the northeast monsoon (retreating monsoon) begins to blow, which affects the coasts that are unprotected from the wind coming from the sea, as the case for Samui.


Like we previously stated; due to Thailand’s tropical savanna climate; the weather is usually hot and humid around the year in Samui. However, the humidity here is noticeably less than Phuket.

January and December are the months with the least temperature.

A higher temperature is observed in the period between February and May, yet, the weather here remains colder than in Thailand’s mainland.

The warmest months would be April and May. During summertime, the weather resumes to be intensely hot and sultry, nevertheless, the refreshing sea breezes are always there to make everything better.

The average temperature in Koh Samui is nearly 30 °C (86 °F) during day time and 24/25 °C (75/77 °F) at night.


The sun is mostly shining brightly around all the seasons. This may come along with rain showers and cases of cloudiness.

However, it gets modest during the dry season from the middle of January to April, when the dose of sunshine is just about right.

Tropical Storms

Tropical cyclones may affect several parts in the country including Koh Samui, particularly, typhoons approaching from the east, which, have recently entered the Gulf of Thailand from mid-October to mid-December only.

They may also form at any other time given the sea temperature is always warm. Still and all, Samui’s region is considered a relatively sheltered area, since the Gulf of Thailand rests just in the middle between the place where cyclones are formed “The Bay of Bengal”, and where typhoons arrive from the east “The South China Sea”, and normally proceed to the north; directly affecting Thailand’s continental part.

The Perfect Time to Visit Koh Samui

We can’t say that there is an optimum one time to visit the island; as it depends on each person’s preferences, however, the time with the loudest votes would be the period from mid/late January up until April. February precisely is a favorite for many as it’s slightly cooler than the other months.

You can discover more about the best time to visit Koh Samui here!

Having said that, Koh Samui still offers plenty of activities and fun things to do all year round, so be sure that whenever you decide to hop into that tropical haven; you will absolutely have a blast! And here are some of each season’s finest!

For the heavenly weather

If you’re after the most pleasant weather; go anytime between late December to April when there are just a few spots of rain and lots of sunshine.

From May to September is also a good time; as the weather is usually sunny, yet there is the possibility of showers during the night or in the afternoon.

If you are not a rain lover, then it’s best to avoid the months of November and October; as they are famous with rainy showers.

For Money Saving

Your best deal would be in the months of April, May, and June; during this period the climate gets very hot and humid, yet looking at the bright side; there are few tourists and plenty of sunshine.

For Snorkeling and Day Trips

A snorkeling trip to Koh Tao is a quite popular activity when you’re spending time at Koh Samui (not a great snorkeling destination itself). And the best time for that would be anytime but November and early December.

March, April, and May are the way to go for spotting some huge whale sharks.

Low Season

In the time of the rainiest months of the year; October and November. However, the possibility of a ravishing sunny day can still happen.

Shoulder Season

The shoulder season occurs during the months of February, March, April, May, June, September, and early December with guaranteed sunny days and pleasant beach weather.

While February and March are the sunniest and driest months in the year.

High Season

It takes place in July and August, late December, and January.

During the high season, you will get amazing warm beach weather. There might be a little rain, yet with a very short duration.

For accommodation booking; try to book your hotels in advance to avoid a fully booked situation, most specifically around Christmas and New Year’s.

Koh Samui Weather and Climate by Month

January Climate and Weather in Koh Samui

January is a great time to visit Samui, as the weather is usually sunny and warm. The average air temperature is 26°C/79°F, and humidity is between 67% and 92%, which will make it feel hotter than the mentioned temperature. Refreshing breezes are forthcoming from the southeast to provide some cooling relief. The sea is quite calm with a water temperature around 26°C/79°F.

There is a slight chance of rain showers; as the rainy season marks its last days over 7 days throughout the first half of the month.

February Weather and Climate in Koh Samui

If you’re after a tropical life experience; February is definitely the perfect choice; with an average temperature of 27°C/81°F. And a low humidity averaging between 63%-90%. The sea is perfectly serene and warm with water temperature around 27°C/81°F.

With such ideal conditions; the month of February is a popular time to visit and a part of the high season on the island.

March Weather and Climate in Koh Samui

The climate of Koh Samui in March is also pleasant; it may be a bit hotter than the previous two, but it’s still among the favored shoulder season.

The air temperature is around 29°C/83°F, the average humidity is between 63%-91% and it keeps rising throughout the month. Gentle breezes approach from the southeast for a reviving touch. The sea temperature is warm with an average of 27°C/81°F.

The underwater visibility is top-notch making this the start of the peak diving and snorkeling season. Moreover, you may easily spot whale sharks.

April Weather Climate in Koh Samui

This is one of the most popular times to visit Samui; this is mainly due to the mix of the sunny hot weather and lack of rainfall. The average temperature is about 29°C/83°F with 80mm of rainfall expected over only five days of the month.

Furthermore, several big events take place during April including Songkran, LGBT Pride Festival, and the Koh Samui Triathlon.

May Weather and Climate in Koh Samui

As long as you’re happy with the heat; you won’t have a problem with the weather during this month. As the temperature hits 30°C/85°F in May and may increase to reach around 34°C/93°F.

With a great dose of sunshine also comes more rainfall with up to 160mm pouring over 9 days, which leads to an increase in humidity, with an average of 62%-92%.

Water temperature resumes its hot season average of 28°C/82°F.

During the last days of the month, water conditions begin to shift as waves get higher due to the winds approaching from the west. Which announces the start of the sailing season, with Samui Regatta highlighting the last week of May.

June Weather and Climate in Koh Samui

The shoulder season is continuing through June with amazing sunny weather with an average temperature of 29°C/83°F and humidity between 61%-90%.

Rainfall is around 100mm, heavy, and with short duration pouring over 9 days.

Water temperature is 28°C/82°F in the east coast. Sea conditions are not that stable on the other side due to the western wind. Anyhow, this means good news for sailors and surfers!

July Weather and Climate in Koh Samui

In July, the weather is generally nice; temperatures are typically hot, however, it may get a bit cloudy during some days with an average temperature of 29°C/83°F and a humidity average between 61%-89%.

Gentle rain showers of 120mm are most likely to occur during the afternoons over 9 days with short durations.

The sea condition is stable with water temperature around 28°C/82°F. Surfing and sailing remain best enjoyed on the west side, while the east coast is quieter and more stable for calmer activities including swimming, snorkeling, and diving.

August Weather and Climate in Koh Samui

The weather is mostly sunny during August with an average temperature of 29°C/83°F and humidity between 61%-88%.

Rainfall is a bit more than other previous months, with an average of 100-110 mm over 10 days.

The western wind resumes blowing making the perfect waves for sailing. While the east-coast holds stable waters with a temperature of 28°C/82°F.

September Weather and Climate in Koh Samui

It is when moods get chiller and temperatures get colder. As September sets the arrival of autumn and school time, the vibes are usually calmer and there are noticeably fewer people on the beaches; making it the perfect time to enjoy a peaceful tropical holiday. The average temperature is around 28°C/82°F and the humidity is between 63%-89%.

Only light showers of 130mm precipitation are foreseen during this month running over eleven days.

Water temperature is about 28°C/82°F; the east coast waters are mostly calm and pleasant, while the waves get a bit tougher on the west side.

October Weather and Climate in Koh Samui

As we mentioned earlier, October is one of the rainiest months of the year with 290 mm rainfall precipitation pouring over 16 days. However, we are still in a tropical wonderland, and the hope of a bright sunny day is never off the list!

The average temperature during October is 27°C/81°F and the humidity average falls between 65%-93%.

This is the perfect month if you are up for a surfing adventure as it marks the beginning of the surfing season. And don’t forget about the great prices.

The water temperature is around 27°C/81°.

November Weather and Climate in Koh Samui

An adventurous wave rider? Then this is the month for you.

November is considered the rainiest month of the year and beats October with a 430mm rainfall precipitation across 15 days, in addition to the biggest waves that are produced by the hefty northern winds.

The weather is still amusing with temperatures around 27°C/81°F and a humidity average between 70%-94%.

December Weather and Climate in Koh Samui

Raying suns and crystal blue skies take a very strong come back during December putting an end to the rainy monsoon season.

There will still be a few rainy days especially during the beginning of the month with only 150mm rainfall precipitation pouring over 9 days, so there is nothing to worry about.

The climate is warm and pleasant as it remains at its lowest of 27°C/81°F average temperature, and a humidity average between 68%-92%.

Water temperature is around 27°C/81°F, with a few nice waves in the catch.

20 Koh Samui Must-Know Tips

As the weather in Koh Samui is unpredictable; sudden climate changes may occur at any time. And these tips may come into handy:

» If you don’t like to get wet; always carry a raincoat and an umbrella.
» Always, always, and always check the weather forecast and set your plans accordingly.
» Don’t walk around without a proper sunscreen that is at least SPF 50.
» If you’re taking the risk and visiting during the monsoon season; make a plan B; for example, if you’re planning to hit the beach for a certain day, also have an alternative indoor activity option.
» A pair of sunglasses and a bottle of water are your vacation buddies.
» Wear light-colored cotton clothes to eliminate the heat.
» A camera should be ready to capture some beautiful creatures in Samui, along with the breathtaking scenery.
» Koh Samui is very popular during Christmas and New Year; so make sure to book everything in advance.
» The best deals are found during the rainy season in October-November.
» September is the ideal month for a relaxing holiday.
» South Chaweng is less crowded and equally charming.
» Other than Chaweng and Lamai beaches; Bo Phut and Maenam are gorgeous and more peaceful options to chill alone or with friends.
» Crystal Beach is a must-visit with its crystal waters and stunning scenery.
» Koh Phangan lies just 30 minutes away from Koh Samui; so make sure not to miss the famous Full Moon Party. We have multiple trips between the two magical islands just right here.
» Stick to street food; it’s everywhere, cheap, and amazingly tasty!
» Most ATMs booths close by 10 pm; they only dispense Thai baht with a limit of THB 20,000 per transaction.
» Don’t miss on Bo Phut night market which takes place every Friday evening at Fisherman’s Village. Another special night market takes place at Lamai Beach on Sundays from 5-10 pm.
» In case of health emergencies; consider Samui International Hospital at Chaweng which offers first-rate medical services. For minor injuries; the government hospital at Nathon will do.
» Renting a car or motorbike is cheaper and much more fun for moving around the island compared to the overpriced unmetered taxis. If you have to get one; fix a price before starting your ride.
» Most importantly; either travel with the people you love or just go by yourself. It’s much more joyful this way.

Please note that this information is subject to change. If you have any doubts or concerns; contact our customer service team via the email, phone, or live chat.

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