December is the tail of Koh Samui’s rainy season: still wet, much less so than November, and busy over the holidays. Below are Thai Meteorological Department (TMD) normals for the island’s station, TMD’s outlook for December 2026, which trips reopen, what is on and how busy it gets. Checked on 27 October 2026.
Koh Samui weather in December: TMD numbers
These are 1991-2020 normals for the Ko Samui station (48 550). A rainy day means 0.1 mm or more. Koh Phangan and Koh Tao have no TMD stations of their own, so Samui is the nearest reference.
| December | Ko Samui (48 550) |
|---|---|
| Average high | 29.3 °C |
| Average low | 24.0 °C |
| Mean temperature | 26.8 °C, the coolest month |
| Rainfall | 263.1 mm |
| Rainy days (0.1 mm or more) | 14.2 |
| Days with thunderstorms | 3.7 |
| Wettest single day, 1991-2020 | 186.0 mm |
| Humidity | 83% |
| Prevailing wind | northeast and east |
How December compares:
| Month | Samui rain, mm | Samui rainy days | Phuket rain, mm |
|---|---|---|---|
| November | 444.6 | 18.7 | 178.2 |
| December | 263.1 | 14.2 | 82.0 |
| January | 126.8 | 11.1 | 49.9 |
| February | 64.3 | 5.6 | 24.0 |
December brings 60% of November’s rain and less than half the thunderstorm days (3.7 against 8.2). It is still the third wettest month of the year after November and October. All months are on Koh Samui weather by month.
TMD outlook for December 2026
From TMD’s cool season outlook issued on 9 October 2026 (no update had appeared by 27 October), for the east coast of the south:
- December: minimum temperatures of 23-25 °C, thunderstorms over 60-80% of the area, heavy to very heavy rain in places, mostly from Surat Thani province southwards. Samui is in Surat Thani province
- Mid-October to early January: heavy rain in many places, with possible flash floods and rivers bursting their banks, then the rain eases as the northeast monsoon weakens
- Waves in the Gulf of Thailand of 2-4 m at times
- November and December: low-pressure systems may become tropical storms crossing the Gulf and the south, with waves of 3-4 m, up to 4-5 m in places
For your dates, check the TMD 7-day forecast under Southern (East Coast), with wind and wave height.
Sea, beaches and boats
In December the Samui station records the wind from the northeast and east, and its mean speed (3.5 knots) is higher than in November (2.9). The east coast beaches, Chaweng and Lamai, face that wind, while the west coast around Lipa Noi is on the lee side. This is our reading of TMD wind data, not a wave measurement, so the flag on the day decides.
Boat trips run on calm days. Keep island tours flexible, pay close to the date and leave them for the second half of your stay. Ferries to Phangan and Tao are on Samui to Koh Phangan and Koh Tao.
What’s open in December
| Place | Status in December 2026 | Foreign adult fee | Source |
|---|---|---|---|
| Ang Thong Marine Park | closed until 15 December, open from 16 December | THB 300 on Ko Wua Talap and Ko Mae Ko, THB 200 elsewhere | DNP |
| Koh Tao and Nang Yuan | open, no national park, trips depend on the sea | no DNP fee | our trip page |
| Big Buddha, Wat Phra Yai | open, on land | no fee found | our sight page |
| Na Muang waterfalls | open, plenty of water, slippery trails | no official fee found | our sight page |
Ang Thong’s annual closure of 1 November-15 December is in the DNP closure table (data as of 7 January 2026), fees in the DNP table for individuals (2 June 2023), children pay half.
What to do on Koh Samui in December
- Ang Thong from 16 December. The main day trip from Samui: Emerald Lake and the Ko Wua Talap viewpoint. Book for a calm day and keep a spare one
- Koh Tao and Nang Yuan. A full day by catamaran, best on a calm morning, see Koh Tao and Nang Yuan from Samui
- On land between showers. The Big Buddha, the Na Muang waterfalls (first fall only after heavy rain) and Fisherman’s Village in Bophut
- Koh Phangan. A short ferry hop, see the Koh Phangan travel guide
All trips from the island are on Samui excursions.
Holidays and events
| Event | Date | Where | Source |
|---|---|---|---|
| Ang Thong Marine Park reopens | 16 December | west of Samui | DNP |
| New Year’s Day | Friday 1 January 2027, public holiday | nationwide | Bank of Thailand |
National holidays in December, from Father’s Day on 5 December to New Year’s Eve, are listed in Thailand in December. As of 27 October TAT and Samui’s municipality had not published Christmas or New Year programmes for the island, and we found no other confirmed December events on Samui.
Crowds and hotel occupancy
The Ministry of Tourism and Sports (MOTS) counts hotel occupancy for Surat Thani province as a whole: Samui, Phangan, Tao and the mainland. December 2025 was its busiest month at 83.54%, up from 73.70% in November, with 515,398 Thai and 411,162 foreign visitors. In other words, the holidays fill the island even in the rain. Book early for Christmas and New Year. We do not publish hotel rates until we collect our own dated measurements.
Should you go to Koh Samui in December?
Go if:
- you come in the second half of the month and want Ang Thong
- a few wet days do not spoil the trip for you
- you want Samui for Christmas or New Year and have booked early
Choose another month or island if:
- you need a dry beach week: Phuket gets 82.0 mm in December, see Phuket in December
- you can move the trip: Samui is driest from February to April
Getting there: Bangkok to Koh Samui and Phuket to Koh Samui. The month before is Koh Samui in November, and the island guide is the Koh Samui holiday guide.
FAQ
Is it rainy on Koh Samui in December?
Often, yes. TMD 1991-2020 normals give 263.1 mm of rain on 14.2 days in December, with thunderstorms on 3.7 days. That is about 60% of November's rain, but three times Phuket's 82.0 mm in the same month. Rain falls further in January (126.8 mm) and is lowest in February (64.3 mm).
Is the sea rough on Koh Samui in December?
It can be. TMD's outlook gives the Gulf of Thailand waves of 2-4 m at times from mid-October to early January, and the December wind at the Samui station blows from the northeast and east. The east coast beaches, Chaweng and Lamai, face it. Follow the flag and the lifeguards.
Is Ang Thong Marine Park open in December?
From 16 December. The DNP closure table lists the whole park as closed from 1 November to 15 December every year. Day trips also depend on the sea, so pick a calm day and keep the booking flexible. The fee is THB 300 for a foreign adult on Ko Wua Talap and Ko Mae Ko, where tours stop.
Is Koh Samui busy at Christmas and New Year?
Yes, despite the rain. MOTS reports 83.54% hotel occupancy for Surat Thani province, which includes Samui, in December 2025, its highest month of the year. Book rooms and flights early if you are coming for the holidays.
Is late December better than early December on Samui?
TMD does not publish weekly normals. Its 2026-2027 outlook expects heavy rain on the southern Gulf coast from mid-October to early January, easing after that. Late December has two practical advantages: Ang Thong is open from 16 December, and January is drier.
Should I choose Phuket or Koh Samui in December?
For dry weather, Phuket: 82.0 mm of rain on 10.3 days against Samui's 263.1 mm on 14.2 days by TMD normals. Samui works in December if you accept some wet days, come after Ang Thong reopens on 16 December and book early for the holidays.
Sources
- TMD. Climatological Data of Thailand for 30 Year Period (1991-2020), Ko Samui (48 550), printed p. 71, and Phuket (48 564), printed p. 82
- TMD. Cool season outlook for Thailand 2026-2027, issued 9 October 2026 (Thai)
- TMD. Seasonal forecasts page
- TMD. 7-day weather forecast by region
- DNP. Opening and closing of tourism in national parks (closure table, data as of 7 January 2026)
- DNP. Entrance fees for individuals (CSV, edition of 2 June 2023)
- MOTS. Tourism statistics by province 2025, monthly sheets (xlsx)
- Bank of Thailand. Notification No. 37/2569, holidays for 2027 (unofficial English translation)
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