Koh Samui in December — Weather, Rain & Is It Worth It?

Overview

December is worth visiting Koh Samui for, but it is really two different months stitched together: a damp, quieter first half still shaking off November’s monsoon, and a dry, packed, expensive second half that is the island’s busiest fortnight of the year. Rainfall averages 265 mm over 12 days for the month as a whole, down from November’s 445 mm over 16 days but still well above January’s 125 mm over 8 days — the number that matters is when in December you land, not the monthly average.

Key takeaways

• December averages 265 mm of rain over 12 days, tapering down 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 guaranteed dry season
• Hotel and villa prices jump hard around 20 December — book 3-6 months ahead for that window
• Highs run 29.3°C, lows 24.0°C, sea holds at 28.5°C, and sunshine averages 5.5 hours a day
• Na Muang and Hin Lad waterfalls are still running strong, fed by November’s rain

---

Koh Samui December Weather — The Two Decembers

Koh Samui’s December splits into a wet first half and a dry second half, and treating the 265 mm monthly average 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 in feel to the tail end of the rainy season rather than true dry season. By the third week, the pattern flips fast: rain days thin out, skies clear, and the island settles into the same dry stretch that runs through January and February.

Highs average 29.3°C and lows 24.0°C for the month, comfortable either half — figures from climatestotravel.com’s 1991-2020 climate normals, the same source behind this site’s 12-month climate table. The difference between the two halves is entirely about rain risk and, as the next section covers, price.

---

The Price Cliff Around 20 December

The single most useful fact for a December trip to Koh Samui is that prices do not rise gradually through the month — they jump on roughly 20 December and stay elevated through New Year. A room that runs 2,500-4,000 THB (~71-114 USD) in early December can double or triple once the holiday fortnight starts, and many resorts add 3-7 night minimum-stay rules on top of the higher rate. The Christmas and New Year guide covers the gala dinners, party venues and exact price bands for that fortnight in full — this page is about the weeks around it.

Because the cliff is sharp rather than gradual, the booking calendar matters more than usual. Book 3-6 months ahead for any stay from 20 December through the first days of January, following the timeline in the when to book guide — villas specifically can sell out by mid-year for the best properties. A trip in the first two or three weeks of December, by contrast, can often be booked just 4-8 weeks out at close to shoulder-season rates, which makes early December the better-value window inside an otherwise expensive month.

---

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 — useful if your dates fall before the 20th and you want swimming days you can count on. 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 island’s biggest concentration of beach clubs gearing up for New Year’s Eve. The trade-off is that these two beaches carry the steepest price increases and the most crowded sand of any month. See the sea conditions by month guide for how each coast behaves week by week through the transition.

---

Waterfalls Still Running Strong in December

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

---

Sea Conditions in December — Warm Water on Every Coast

Sea temperature holds at a swimmable 28.5°C on every coast in December, so cold water is never the issue — sea state is. The north coast (Maenam, Bophut) stays merely choppy through December, 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 that defines the dry season through February. Full coast-by-coast detail, including tides and jellyfish risk, is in the sea conditions by month guide.

---

Hiking After the Wet Season

Trails are at their greenest but muddiest early in December, drying out fast as the month clears. The Na Muang Waterfalls Trail and Hin Lad Waterfall Trail both 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 conditions by mid-to-late month. Exposed viewpoint routes with less tree cover handle the transition better than jungle trails, since they dry faster after a shower; the full 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 in full.

---

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 own New Year’s Eve countdown, along with the gala dinners and beach-club parties that define the last week of the month, are covered in full in the Christmas and New Year guide rather than repeated here. Crowds build steadily from the third week onward and peak from 26 December through 2 January, the busiest stretch on the island’s calendar.

---

What to Pack for December

Pack for both halves of the month: a light rain jacket or packable poncho for early December’s leftover showers, plus standard dry-season kit — reef-safe sunscreen, a hat, and light layers for breezy evening boat trips — for the back half. A dry bag is worth carrying in the first two weeks in case an afternoon squall catches you outside; by Christmas week it becomes optional. See the trip cost guide for a full budget breakdown across December’s price swing, and the wider best time to visit guide for how the month compares to the rest of the year.

---

FAQ

Is December a good time to visit Koh Samui?

Yes, especially the second half. Early December still carries leftover rain from November — roughly 265 mm falls across 12 days for the month — but by Christmas week the island is in its dry-season pattern, with highs around 29.3°C and sea temperature at 28.5°C. The trade-off for that better weather is sharply higher prices after 20 December.

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 out fast after that, and December’s 265 mm/12 days is already a big drop from November’s 445 mm/16 days. By the back half of the month, rain risk is close to January’s dry-season level.

When do Koh Samui’s December prices peak?

Prices jump sharply around 20 December and stay high through New Year, rather than rising gradually across the month. A room that costs 2,500-4,000 THB (~71-114 USD) in early December 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 any leftover monsoon swell. Chaweng and Lamai suit the second half, once seas calm and the island’s biggest nightlife and New Year’s Eve scene kick in — though both carry the steepest price increases of any beach on the island 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 start fading gradually as the dry season deepens toward March and April. December is a good window to see them near full flow without October-November’s harder rain underfoot.

Is the sea calm in Koh Samui in December?

It is improving through the month rather than 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 that defines the dry season by late month.