Koh Samui Weather December: 265 mm Rain, 29.3°C, Sea 28.5°C

Is December a Good Time to Visit Koh Samui?

Koh Samui weather in December is two months in one: a damp first half still shaking off November’s monsoon, then a dry, packed, expensive second half. The monthly averages are 29.3°C highs, 24.0°C lows, a 28.5°C sea and 265 mm of rain over 12 days, down from November’s 445 mm over 16 days but well above January’s 125 mm over 8. Yes, December is worth it, and the number that matters is when in the month you land, not the average.

Key takeaways

• 265 mm of rain over 12 days, tapering from November’s 445 mm/16 days toward January’s 125 mm/8 days
• The first 1-2 weeks still carry real rain risk; the back half is close to dry season
• Highs 29.3°C, lows 24.0°C, sea 28.5°C, sunshine 5.5 hours a day
• Hotel and villa prices jump around 20 December: book 3-6 months ahead for that window
• Na Muang and Hin Lad waterfalls are still running strong, fed by November’s rain

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Koh Samui Weather in December: The Numbers

The table below uses Climates to Travel’s 1991-2020 climate normals, cross-checked against the Thai Meteorological Department (Sep 2026) and shared with this site’s 12-month climate table. They are long-term averages, not a forecast for one specific December, so they apply to 2025, 2026 or any other year alike.

Temperature barely moves across the shift: the risk in December is rain and sea state, never heat or cold.

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What Is the Temperature and Climate in Koh Samui in December?

Highs average 29.3°C and lows 24.0°C, so days are warm and evenings comfortable in either half of the month. The climate is tropical monsoon: December is the tail of Samui’s October-December wet season, driven by the northeast monsoon, which is why the island’s rain pattern runs opposite to the Andaman coast (Phuket, Krabi). The sea is 28.5°C, half a degree below November and half a degree above January. The rainy season guide explains the full October-December window.

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Koh Samui December Weather: The Two Decembers

Koh Samui’s December splits into a wet first half and a dry second half, so treating 265 mm as a single forecast misses the point. Roughly the first 10-14 days still inherit some of November’s northeast monsoon: expect a real chance of an afternoon downpour, similar to the tail end of the rainy season. By the third week the pattern flips: rain days thin out, skies clear and the island settles into the dry stretch that runs through January and February.

The difference between the halves is entirely about rain risk and, as the next section covers, price.

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Koh Samui in Early December: What the First Weeks Are Like

Early December is the value window: showers are still possible, but rates sit close to shoulder-season levels and the crowds of the holiday fortnight have not arrived. A trip in the first two or three weeks can often be booked just 4-8 weeks out (the when to book guide has the timeline for the holiday fortnight). Expect the first week or two to be the wettest part of the month, with an afternoon squall as the main risk, and plan mornings for the beach. The north coast (Maenam, Bophut) is the sheltered pick in these weeks, covered below.

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The Price Cliff Around 20 December

The most useful fact for a December trip is that prices do not rise gradually: they jump on roughly 20 December and stay high through New Year. A room that runs about 71-114 USD (2,500-4,000 THB) a night in early December (as of 2026) can double or triple once the holiday fortnight starts, and many resorts add 3-7 night minimum-stay rules. The Christmas and New Year guide covers the gala dinners, party venues and price bands for that fortnight. This page is about the weeks around it.

Because the cliff is sharp, the booking calendar matters. Book 3-6 months ahead for any stay from 20 December through the first days of January, following the when to book guide. Villas can sell out by mid-year for the best properties. The first two or three weeks of December are the better-value window inside an otherwise expensive month, and prices ease again after the first week of January.

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Which Beaches Suit December: Early Rain vs Late Peak

Early December favors the north coast, where showers pass without much sea disruption; late December favors wherever you can still get a room, since the whole island fills up. Maenam and Bophut sit more sheltered from the tail end of the northeast monsoon than the east coast, so a stray early-month downpour is less likely to come with rough water. Bophut’s Fisherman’s Village also keeps its Friday walking street running regardless of the weather.

Once the island dries out and fills up in the back half of the month, Chaweng and Lamai come into their own: calmer seas, the busiest nightlife of the year and the biggest concentration of beach clubs gearing up for New Year’s Eve. The trade-off is the steepest price increases and the most crowded sand of any month. The sea conditions by month guide shows how each coast behaves week by week.

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Waterfalls Still Running Strong in December

December’s waterfalls still benefit from November’s 445 mm of rain, so both main falls run at good volume through most of the month even as skies clear. Na Muang Waterfall keeps a strong flow into its swimmable pool, and Hin Lad Waterfall (closer to Nathon, along a shaded jungle trail) is similarly full. Both fade gradually as the dry season progresses toward March-April, so December is a good window to see them near their best without the harder rain that made footing difficult in October and November.

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Sea Conditions in December: Warm Water on Every Coast

Sea temperature holds at a swimmable 28.5°C on every coast, so cold water is never the issue: sea state is. The north coast (Maenam, Bophut) stays merely choppy, a leftover from the northeast monsoon, while the east coast (Chaweng, Lamai) is still working through the last of its rougher October-November swell early in the month before calming down. By the back half of December the whole island trends toward the calm, clear water of the dry season through February. Coast-by-coast detail, including tides and jellyfish risk, is in the sea conditions by month guide.

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Hiking After the Wet Season

Trails are greenest but muddiest early in December, drying out fast as the month clears. The Na Muang Waterfalls Trail and Hin Lad Waterfall Trail benefit from the same recent rain that keeps the falls full: expect slick, root-covered sections and standing puddles in the first week or two, easing to firm, green trail by mid-to-late month. Exposed viewpoint routes dry faster after a shower than jungle trails; the waterfalls and hikes guide breaks down conditions trail by trail. Start hikes before 9 am regardless of the date: heat builds quickly once the December sun is out.

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Events and Crowds in December

December’s event calendar peaks around the same dates that drive the price cliff. A Full Moon Party lands on Koh Phangan on 24 December most years, pulling a wave of overflow bookings onto Samui’s hotels and ferries the same week; see the full moon party from Samui guide for transfer timing. Chaweng’s New Year’s Eve countdown, gala dinners and beach-club parties are covered in the Christmas and New Year guide. Crowds build from the third week and peak from 26 December through 2 January, the busiest stretch on the island’s calendar.

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What to Pack for December

Pack for both halves of the month: a light rain jacket or packable poncho for early December’s showers, plus standard dry-season kit (reef-safe sunscreen, a hat, light layers for breezy evening boat trips) for the back half. A dry bag is worth carrying in the first two weeks; by Christmas week it becomes optional. The trip cost guide covers December’s price swing, and the best time to visit guide shows how the month compares with the rest of the year.

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FAQ

What is the weather like in Koh Samui in December?

Warm with a wet start and a dry finish: 29.3°C highs, 24.0°C lows, 5.5 sun hours a day, 265 mm of rain over 12 days and a 28.5°C sea, per Climates to Travel’s 1991-2020 normals. Rain risk is concentrated in the first one to two weeks.

Should I go to Koh Samui in December?

Yes, especially the second half. Early December still carries leftover rain from November, but by Christmas week the island is in its dry-season pattern. The trade-off is sharply higher prices after 20 December. For value, go in the first two or three weeks.

Does it still rain in Koh Samui in December?

Yes, mainly in the first one to two weeks, which carry the tail end of November’s monsoon. Rain thins fast after that: December’s 265 mm over 12 days is already a big drop from November’s 445 mm over 16, and the back half is close to January’s dry-season level.

What is the rainiest month in Koh Samui?

November, at about 445 mm over 16 rain days, followed by October at 295 mm and December at 265 mm. See the rainy season guide for the October-December window in full.

Which month should you avoid in Koh Samui?

For rain, November: the wettest month at 445 mm, with October (295 mm) next. December’s first half is the tail of that wet stretch, so travelers who dislike showers should aim for the last ten days or January instead.

Is it rainy in Thailand in December?

It depends on the coast. Koh Samui’s wet season is October-December, driven by the northeast monsoon, so early December can be showery here. The pattern is opposite to the Andaman coast (Phuket, Krabi), which has its rain in the middle of the year.

When do Koh Samui’s December prices peak?

Prices jump sharply around 20 December and stay high through New Year, rather than rising gradually. A room at about 71-114 USD (2,500-4,000 THB) in early December (as of 2026) can double or triple for the holiday fortnight, so book 3-6 months ahead for any stay after the 20th.

Which beach is best for a December trip to Koh Samui?

Maenam and Bophut suit the first half, staying more sheltered from leftover monsoon swell. Chaweng and Lamai suit the second half, once seas calm and nightlife and New Year’s Eve kick in, though both carry the steepest price increases that week.

Are Koh Samui’s waterfalls still flowing in December?

Yes. Na Muang Waterfall and Hin Lad Waterfall are both still running strong in December, fed by November’s heavy rain, and only fade gradually as the dry season deepens toward March and April.

Is the sea calm in Koh Samui in December?

It improves through the month rather than being calm from day one. Sea temperature holds at 28.5°C throughout, but the east coast is still working through late monsoon swell early in December before both coasts settle into the calmer water of the dry season.