Koh Samui in January is the start of the island’s best stretch of weather. The north-east monsoon is fading, rain falls on far fewer days than in November or December, and the sea calms down more often as the month goes on. It is also high season, so the island is busy and prices stay firm.
For our crew, January is when weather cancellations become much less common. This guide covers the weather and sea in numbers, how crowds and prices change through the month, the dates worth knowing for 2027, and why January suits a day out to Koh Tan, Pig Island and the Five Islands.
Quick answer: January averages about 127 mm of rain on 8–9 days, with highs around 29°C. Early January can still bring leftover swell and the odd wet spell; the second half is usually calmer and sunnier. It is a good month for boat trips. The New Year week is the busiest, and Chinese New Year falls on 6 February in 2027, not in January.
Quick facts
| Average temperatures | High 29.0°C, low 24.2°C (WMO averages, 1991–2020) |
| Average rainfall | About 127 mm, on around 8–9 days with 1 mm or more |
| Sunshine | About 6.4 hours a day on average, rising to about 7.6 in February |
| Recent Januaries | 2025: 141.1 mm at Ko Samui, slightly above normal. 2026: 54.2 mm, well below normal (Thai Meteorological Department) |
| Sea | Calmer most days, with the occasional windy surge, mainly early in the month |
| Ang Thong Marine Park | Open, weather permitting (it reopens after the annual closure in mid-December) |
| Busiest days | 1 January to roughly the end of the first week |
Koh Samui in January: the weather in numbers
These are the World Meteorological Organization’s 30-year averages for the Ko Samui station (WMO climate normals, 1991–2020), with the months either side.
| Month | Avg high | Avg low | Rainfall | Rainy days | Sun (hrs/day) |
|---|---|---|---|---|---|
| December | 29.3°C | 24.0°C | 263 mm | 11.6 | 5.7 |
| January | 29.0°C | 24.2°C | 127 mm | 8.5 | 6.4 |
| February | 29.4°C | 24.9°C | 64 mm | 4.3 | 7.6 |
January gets about half of December’s rain, and roughly two days in three stay dry. It is one of the slightly cooler months, which most people find comfortable rather than cool. Nights sit around 24°C.
The year-to-year swing is large. The Thai Meteorological Department’s monthly summaries show January 2025 at 141.1 mm for Ko Samui, a little above normal, with a strong wind and cold surge along the Surat Thani coast. January 2026 was much drier at 54.2 mm, though the monsoon still strengthened for a few days from 6 to 8 January and brought heavy rain to parts of the east coast of the south. Bad Januaries do happen: in January 2017, flooding across southern Thailand reached Samui, and some flights and ferries were delayed or cancelled.
Early January versus late January
The first week or so is a transition. The monsoon can still push a few windy, showery days across the Gulf, and the sea can stay lumpy after them. By the second half of the month, settled days are more common, the water clears, and sunshine hours climb towards February’s levels. If you can choose, the second half of January is the safer bet for sea days.
Why January suits boat days to Koh Tan, Pig Island and the Five Islands
For a boat trip, the sea matters more than the rain, and January is when the Gulf around Samui starts to calm down for longer stretches. Fewer days are lost to wind than in November or December, and snorkelling visibility usually improves once there have been a few settled days in a row.
Koh Tan
Koh Tan, off the south coast, is the easiest snorkelling from Samui. On a calm January day the reef close to the beach is good for beginners. After a windy spell, give it a day or two to clear. Our Koh Tan snorkelling guide has the detail.
Pig Island (Koh Madsum)
Pig Island is a short hop from Koh Tan, and it sits outside Ang Thong National Park, so park closures never affect it. The beach landing is easier when the sea is flat, which in January is most days. Read the Pig Island rules before you go.
The Five Islands
The limestone cliffs of the Five Islands (Koh Si Koh Ha) stand in more open water off Taling Ngam, so they are the stop most affected by swell. Calm January mornings are a good time to see them up close from the boat.
What can still go wrong
- Cold surges. Pushes of cold air from China can strengthen the north-easterly wind for a few days, as in January 2025, and stir up the Gulf.
- Leftover swell early in the month, even on sunny days.
- Small boats feel it first. A longtail from Thong Krut may stay in on a day when a bigger boat can still sail comfortably. On truly rough days, nobody should sail.
If the sea is not safe on your date, we move your trip to a new date first, and give a full refund if the new date is also bad. Cancellation is free up to 24 hours before pickup.
Planning a January sea day?
The Samui Journey 1-Day Catamaran sails from Bang Kao Pier to the Five Islands, Koh Tan for snorkelling and Pig Island, with kayaks, paddleboards, a water slide, a springboard, a banana boat (age 5+), a Thai massage, lunch, drinks and hotel transfers included. Adults ฿3,300, children (5–11) ฿1,900, under 5s free. Check dates and book or ask us on WhatsApp: +66 94 751 4988.
Ang Thong in January
Ang Thong National Marine Park reopens after its annual closure in mid-December, so it is open in January when the weather allows. It is a longer crossing than the islands off the south coast, and the park can still cancel trips in rough weather. If you only have one boat day, our Ang Thong or Pig Island comparison sets out the trade-offs.
Crowds and prices in January
- 1 January to about the end of the first week: still peak holiday season. Rooms are at their most expensive, many resorts keep minimum stays, and tours fill up.
- Middle of the month: noticeably quieter once most European school holidays end, though January stays high season. Hotel rates usually ease a little, not a lot.
- Late January: steady, with many long-stay visitors escaping winter. In years when Chinese New Year falls in late January, as it will on 26 January 2028, the island gets busier again around the holiday.
Book boat trips a few days ahead throughout January, and earlier for the New Year week. If your dates include a Friday, our Fisherman’s Village guide covers the walking street market.
Events and dates in January 2027
- 1 January (Friday): New Year’s Day, a public holiday. Expect a slow, quiet morning across the island after the night before.
- 9 January (Saturday): Thai Children’s Day, held on the second Saturday of January. Many government offices and some temples hold activities for children.
- Around 22 January: full moon. Koh Phangan’s Full Moon Party is usually held around this date; confirm with the organisers, as dates can shift.
- Chinese New Year: in 2027 it falls on Saturday 6 February, so the Chinese New Year crowds arrive in early February, not January.
What to pack for January
- Light clothes, plus one long-sleeved layer for air-conditioned rooms and evenings after rain.
- A compact rain jacket, mostly for the first half of the month.
- Reef-friendly sunscreen and a hat; with more sunshine and a breeze on deck, sunburn on the water is easy to underestimate.
- A dry bag for your phone on boat days.
Our boat day packing list covers the rest.
A simple January plan
- Day 1 or 2: the boat day. Put your sea trip early, so you have spare days if the forecast changes.
- A beach day on the east coast if the flags are green, or Choeng Mon and Bophut if the wind is up. Our best beaches in Koh Samui guide compares them.
- A land day: temples, Namuang Waterfall and viewpoints on the Explore the Real Samui 4×4 Island Safari (from ฿1,950 per adult), or a half-day at Samui Elephant Kingdom, an ethical sanctuary we support and book visits to (adults ฿3,000).
- A spare day for a postponed boat trip, or for doing nothing.
For longer stays, our Koh Samui 5-day itinerary lays out a full week’s rhythm.
Is Koh Samui in January a good time to visit?
Yes, for most travellers. It has warm, mostly dry weather, a calmer sea than at any point since October, and the island is green after the rains. It suits first-timers, families and anyone whose trip is built around a boat day.
The downsides: it is high season, so rooms cost more than in the shoulder months, and the first week is crowded. A run of windy days can still happen, particularly early on. If you want the driest, calmest odds of the year, February to April edges ahead; compare the months in our best time to visit Koh Samui guide.
FAQ
Is January a good time to visit Koh Samui?
Yes. Rain falls on about 8–9 days on average, highs are around 29°C, and the sea is calm more often than in November or December. The first week is busy and expensive.
Does it rain in Koh Samui in January?
Sometimes. The long-term average is about 127 mm, mostly in short showers. Early January can still bring a wet spell as the monsoon fades, and some years are wetter than others.
Is the sea calm enough for boat trips in January?
Usually, yes, especially in the second half of the month. Windy surges can still cancel the odd day, so book your boat trip early in your stay.
Is Ang Thong open in January?
Yes. It reopens after the annual closure in mid-December, though trips can still be cancelled when the sea is rough.
When is Chinese New Year in 2027?
Saturday 6 February 2027. In 2028 it falls earlier, on 26 January.
Is Koh Samui crowded in January?
The first week, yes. After that it is still high season but noticeably calmer, with long-stay visitors and couples more than holiday crowds.
