Koh Samui Weather
Gulf of Thailand · Live forecast, monthly climate & best time to visit
28°C
Partly cloudy · Koh Samui, right now
Is it raining right now in Koh Samui?
No — Koh Samui is dry right now (partly cloudy, 28°C).
Thu
29°24°
💧 80%
Fri
28°23°
💧 91%
Sat
27°23°
💧 94%
Sun
27°22°
💧 97%
Mon
26°22°
💧 95%
Tue
27°22°
💧 93%
Wed
26°22°
💧 83%
Best time to visit Koh Samui
Thailand doesn't have a single rainy season — it has two, running in opposite directions. The Andaman coast (Phuket, Krabi) faces the Indian Ocean and takes the brunt of the southwest monsoon from roughly May to October. The Gulf of Thailand coast around Koh Samui faces the other way and instead gets its wettest weather from the northeast monsoon around October to December — often staying drier during the mainland's rainy season. Bangkok and the upper Gulf (Pattaya, Hua Hin) follow the same broad May–October pattern as the Andaman coast, while Chiang Mai and the north add a hot, hazy “burning season” from around February to April.
For Koh Samui specifically: Jan–Apr sees the fewest rain days of the year, while Jul–Dec is the wettest stretch. Rain rarely lasts all day — see the FAQs below for what to expect.
Koh Samui monthly climate
| Month | Avg. high | Rainy days | What to expect |
|---|---|---|---|
| January | 29°C | 9 days | Tail end of the wet season, about 127 mm; showers still possible but skies are clearing. |
| February | 29°C | 4 days | The driest month of the year, about 64 mm of rain. |
| March | 30°C | 5 days | Hot, dry and sunny — a top month for beaches and diving. |
| April | 32°C | 6 days | Hot with the odd short storm; Songkran adds festivities. |
| May | 33°C | 11 days | A brief shower season begins but rarely disrupts a full day outdoors. |
| June | 33°C | 10 days | A quiet dry pocket between the two monsoon seasons. |
| July | 32°C | 11 days | Generally dry with pleasant sea breezes. |
| August | 32°C | 11 days | Rain on about one day in three, around 100 mm; still a solid beach month. |
| September | 32°C | 11 days | Much like August, about 118 mm; the northeast monsoon has not arrived yet. |
| October | 31°C | 16 days | Wet season begins in earnest, about 295 mm; unlike the rest of Thailand, Samui's rains are still building. |
| November | 30°C | 17 days | The wettest month of the year, about 445 mm; heavy rain and rough seas are common. |
| December | 29°C | 12 days | Still wet early in the month, about 263 mm, gradually clearing by the end. |
Source: World Meteorological Organization 1991-2020 climate normals for the Ko Samui station (WMO 48550): mean daily maximum and days with 1 mm of rain or more, checked 2026-09-30. Normals, not a forecast. Corrected on 30 September 2026: the table used to give 17 rain days in December against 12 in the normals, 12 in January against 9, one more in October and November, and 1 to 2 fewer from May to August; highs were 1 to 2°C too low from April to January. November stays the wettest month, with about 445 mm.
Packing & season tips
- Pack for Koh Samui: Beachwear and sun protection for most of the year, but pack a proper rain jacket — not just an umbrella — if visiting October–December.
- Sun protection: Thailand's tropical latitude means strong UV year-round, even on cloudy or rainy days.
- Book ahead in peak season: the driest months are also the busiest and most expensive for flights and hotels.
- Rainy season isn't a reason to skip a trip: expect lower prices, fewer crowds and lush scenery — just plan indoor backup options for late afternoons.
Frequently asked questions
When is the best time to visit Koh Samui?
Jan–Apr tends to be the best window — rainfall is well below the yearly average and days are more reliably sunny. Avoid Jul–Dec if you'd rather not plan around rain.
Does it rain all day during the rainy season in Koh Samui?
Usually not. Thailand's monsoon rain typically falls as short, heavy afternoon or evening downpours that clear within an hour or two, rather than all-day drizzle — mornings are often dry even in the wettest months.
Is Koh Samui hot all year round?
Yes — average daytime highs run from about 29°C in the coolest month to 33°C in the hottest, so it's warm to hot year-round by most visitors' standards. Humidity, not just temperature, is what changes most through the year.
What should I pack for Koh Samui?
Beachwear and sun protection for most of the year, but pack a proper rain jacket — not just an umbrella — if visiting October–December.
Why is Koh Samui's rainy season different from the rest of Thailand?
Koh Samui sits on the Gulf of Thailand side of the peninsula, which faces the northeast monsoon rather than the southwest monsoon that soaks the Andaman coast and mainland from May to October. That flips Samui's wettest months to roughly October–December, while it often stays drier during the mainland's rainy season.