Koh Samui in January
Drying outHighs of 29°C and lows of 24°C, 127 mm of rain on about 8 days, sea at 28°C.
Out of the rainy season, with a few showers still normal. High season, with the crowds thinning after New Year.
Destination guide
Best Time to Visit Koh Samui
Good from January to August, driest in February, and wettest in November.
- Best for
- beach lovers, families
- Logistics
- Easy
- Updated
- 2 Oct 2026
By Mac Kiley · 3 min read
When Is the Best Time to Visit Koh Samui?
The best time to visit Koh Samui is January to August, with the driest weather from February to April. Samui runs on a different clock from Phuket. The Gulf islands are sheltered from the southwest monsoon that soaks the Andaman coast from May to October, so Samui stays mostly sunny through the summer, then gets its own rainy season from October to December, wettest in November. That makes Samui, Koh Phangan and Koh Tao the beach answer for July and August, and the islands to avoid in November.
Koh Samui Weather by Month
Averages for the Ko Samui weather station. Koh Phangan and Koh Tao follow the same pattern. Tap a month to jump to it.
| Month | High | Low | Rain | Rain days | Sea | Verdict |
|---|---|---|---|---|---|---|
| January | 29°C | 24°C | 127 mm | 8 | 28°C | Drying out |
| February | 29°C | 25°C | 64 mm | 4 | 28°C | Driest month |
| March | 30°C | 25°C | 116 mm | 5 | 29°C | Dry and calm |
| April | 32°C | 26°C | 83 mm | 6 | 30°C | Dry and hot |
| May | 33°C | 26°C | 132 mm | 11 | 30°C | Hottest, mostly dry |
| June | 33°C | 25°C | 134 mm | 10 | 30°C | Mostly sunny |
| July | 32°C | 25°C | 117 mm | 11 | 30°C | Sunny spells |
| August | 32°C | 25°C | 102 mm | 10 | 29°C | Decent |
| September | 32°C | 25°C | 118 mm | 11 | 29°C | Mostly fine |
| October | 31°C | 24°C | 295 mm | 16 | 29°C | Rains begin |
| November | 30°C | 24°C | 445 mm | 16 | 29°C | Wettest month |
| December | 29°C | 24°C | 263 mm | 12 | 28°C | Wet early, clearing |
Koh Samui in February
Driest monthHighs of 29°C and lows of 25°C, 64 mm of rain on about 4 days, sea at 28°C.
The driest month of the year, with calm seas and long sunny days. The best month for Ang Thong Marine Park and boat trips to Koh Phangan and Koh Tao.
Koh Samui in March
Dry and calmHighs of 30°C and lows of 25°C, 116 mm of rain on about 5 days, sea at 29°C.
Still dry and calm, a little hotter, and quieter than the winter peak. One of the best months for a beach week.
Koh Samui in April
Dry and hotHighs of 32°C and lows of 26°C, 83 mm of rain on about 6 days, sea at 30°C.
Dry and hot, with calm water. Songkran (13–15 April) brings water fights to the main beach towns.
Koh Samui in May
Hottest, mostly dryHighs of 33°C and lows of 26°C, 132 mm of rain on about 11 days, sea at 30°C.
The hottest month on the island and still mostly dry, while the Andaman coast gets the monsoon. Prices drop after high season.
Koh Samui in June
Mostly sunnyHighs of 33°C and lows of 25°C, 134 mm of rain on about 10 days, sea at 30°C.
Sunny spells and occasional showers, with much less rain than Phuket. A good-value month for the beach.
Koh Samui in July
Sunny spellsHighs of 32°C and lows of 25°C, 117 mm of rain on about 11 days, sea at 30°C.
Some of the sunniest weeks of the summer, which makes Samui busy with summer-holiday visitors. Book a few weeks ahead.
Koh Samui in August
DecentHighs of 32°C and lows of 25°C, 102 mm of rain on about 10 days, sea at 29°C.
Decent beach weather and calm seas on most days, and still the best beach choice in Thailand in August.
Koh Samui in September
Mostly fineHighs of 32°C and lows of 25°C, 118 mm of rain on about 11 days, sea at 29°C.
Rain starts to build toward the end of the month, but most days are still fine. Quieter, with prices falling.
Koh Samui in October
Rains beginHighs of 31°C and lows of 24°C, 295 mm of rain on about 16 days, sea at 29°C.
The Gulf islands' rainy season starts, with storms on about half the days and rougher seas. Prices are low.
Koh Samui in November
Wettest monthHighs of 30°C and lows of 24°C, 445 mm of rain on about 16 days, sea at 29°C.
The wettest month of the year, with heavy rain on about half the days and rough seas some days. Ang Thong Marine Park closes on 1 November. The month to avoid.
Koh Samui in December
Wet early, clearingHighs of 29°C and lows of 24°C, 263 mm of rain on about 12 days, sea at 28°C.
The tail of the rainy season, with the rain easing as the month goes on. Ang Thong reopens after 15 December, and Christmas and New Year are usually fine.
Figures are 1991–2020 averages for the Ko Samui station from WMO Climatological Standard Normals 1991–2020 (Thai Meteorological Department stations). Rain days count days with at least 1 mm. Sea temperatures: Climates to Travel monthly sea-surface averages.
Arriving in Koh Samui
Where to stay in Koh Samui
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Koh Samui's Rainy Season (October to December)
Most of Thailand's rain comes with the southwest monsoon from May to October, but Koh Samui sits on the Gulf side, sheltered from it. Its wet season comes later, when the northeast monsoon blows in from the South China Sea. October is the transition, November is the wettest month of the year, and December clears as it goes on.
In those months, rain often falls in long, heavy bursts, the east-coast beaches like Chaweng and Lamai can be rough, and ferries to Koh Phangan and Koh Tao run on choppier water. Ang Thong Marine Park closes from 1 November to 15 December. In November and December, the Andaman coast (Phuket, Krabi, Koh Lanta) is the drier choice.
Koh Samui or Phuket? It Depends on the Month
The two islands have nearly opposite rainy seasons. From May to September, Phuket gets the southwest monsoon and Samui is the better beach. October is wet on both. In November and December, Samui gets its heaviest rain and Phuket is the better beach. From January to April both are good, and February is excellent on both. The full side-by-side is on the Phuket vs Koh Samui comparison.
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Written by
Mac Kiley
I lived in Bangkok for four years and traveled the country from there. The guides are my own opinions, written the way I'd explain them to a friend planning a trip.
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