Koh Samui Weather by Month: Best Time to Visit and Where to Swim

The driest month on Koh Samui is February, with around 64 mm of rain. The wettest is November, with roughly 445 mm over 16-17 rainy days. If you can choose your dates, aim for January to April. If your tickets are already booked for November, stay on the west or south coast, where the sea is calmer.

Samui's wettest and driest months differ by almost seven times, and that is the figure to keep in mind when planning. Temperature barely changes through the year: 29-32°C by day, 24-26°C at night, humidity around 70%, and sea water at about 29°C even at the height of the rains. You will not get cold here. The real questions are how much rain falls and how rough the sea gets.

A quick seasonal guide:

• January - February: February is the driest month at about 64 mm. This is the best mix of sunshine, calm seas and reliable boat trips.
• March - May: Dry, but hot and humid. The sea feels like bath water, and shade and air conditioning become essential.
• June - September: Moderately wet. On Samui this is manageable, and while Phuket is battered by the southwest monsoon, life on Samui carries on comfortably.
• October - December: Peak rainy season, with November at ~445 mm and 16-17 rainy days. Expect swell, red flags, cancelled boats and the lowest prices of the year.

One caveat: 445 mm and 64 mm are long-term averages, not a forecast for your specific November or February. Some Novembers are dry, and some Februarys bring a grey week.

Why Samui is wet when Phuket is dry

Samui follows the northeast monsoon, while the Andaman coast follows the southwest monsoon. Their seasons are offset, so in November and December, when Phuket is marketed as the ideal destination, Samui is going through its wettest months. The usual logic that it is equally good everywhere in Thailand in winter does not apply here. A flight from Phuket to Samui in November can take you from sunshine into rain.

The reverse also holds. In summer, when Phuket gets storms and heavy swell, Samui remains a solid choice, and July and August are far calmer here than on the west coast. For context, international travel sources also list the February-March window as Samui's driest, and put the wettest period in autumn through mid-December.

Where to swim in November and December: west and south, not Chaweng

The most common mistake is booking Chaweng or Lamai simply because they are the island's main beaches. During the northeast monsoon the eastern shore takes the full force of the waves: murky water, heavy surf and red flags for days at a time.

These shores are sheltered from the wind at this time of year:

• Lipa Noi: shallow and calm, good with children
• Taling Ngam: quiet, with almost no crowds
• Nathon: next to the ferry pier and local markets
• Thong Krut: in the south, where boats leave for the southern islets

In November and the first half of December, a hotel's value depends on which side of the island it is on, not on its star rating. A hostel on the west coast will give you more swimming than an expensive resort on Chaweng.

Red flags on Samui are not decorative. Rip currents on the eastern shore during the monsoon are fast, and most beaches have no lifeguards.

Early November vs late November: a two-week difference

It helps to treat November as two different months.

1-15 November. Chance of rain is 60-75%, with only 3-5 hours of sun per day and an unsettled sea. Boat excursions are regularly cancelled, and Ang Thong National Marine Park is closed from 1 November to 15 December 2026 because of the swell. If Ang Thong is why you are coming, it simply will not be available on these dates.

16-30 November. The monsoon retreats, rain becomes shorter and less frequent, and boats run more reliably. The month averages about 6 hours of sun per day, more than October's 4.5 hours. That sounds odd for the wettest month, but rain here usually arrives as short, heavy downpours rather than all-day drizzle.

One detail people rarely expect: in mid-November the sun rises around 06:13 and sets at 17:56. Plan beach time for the first half of the day, because the evenings are dark early.

My advice: if your dates are flexible, fly in the second half of November and choose accommodation with free cancellation. Book a hotel on the west coast with flexible terms. It costs less than overpaying for a bad forecast. If your budget is tight and price is all that matters, early November offers the lowest rates of the year, but be ready for spas, cooking classes, temples and waterfalls instead of boat trips.

Choosing dates from scratch

The best compromise is February and March: dry, calm sea and open parks. January is almost as good but pricier because of the New Year tail. April and May suit travellers who handle heat well.

Treat October to December as an option only if you want a cheap, long winter stay rather than two weeks of guaranteed sun. Over a month or more, rain is easy to live with, and there is always a dry window. For a seven-day holiday, it is a lottery.

The advice to avoid November does not apply to remote workers. For a laptop and air conditioning, the gap between 445 and 64 mm hardly matters, while the drop in rental prices is very noticeable.

FAQ

Which month is the rainiest on Koh Samui?

November: about 445 mm of rain and 16-17 rainy days, with daytime highs around 30°C. This is an average, not a forecast for a specific year.

Can you actually swim on Samui in November?

Yes, the water is about 29°C. But choose the west and south coast: Lipa Noi, Taling Ngam, Nathon and Thong Krut. Chaweng and Lamai more often have swell and red flags at this time.

Is Ang Thong open in November?

No. The park is closed from 1 November to 15 December 2026 due to heavy swell. Other boat routes run selectively, depending on the weather.

When is the best weather on Samui?

February and March. February is the driest month of the year at about 64 mm. January is also dry but more expensive.

Why is Phuket sunny while Samui is rainy?

Samui sits in the Gulf of Thailand and follows the northeast monsoon, while Phuket follows the southwest monsoon. The seasons are offset, so in November and December the weather on the two islands is often opposite.

What is the temperature on Samui through the year?

Very stable: 29-32°C by day and 24-26°C at night, with humidity around 70% and sea temperature near 29°C all year.

Is Samui good in summer?

Yes. In July and August it is much calmer than the west coast, so it works well when Phuket is stormy.

Source: UrlaubWow

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