March brings 30°C daytime highs, 21mm of precipitation across about 2 wet days and 12 hours of daylight — best for beach days, swimming and reliable sunshine. The strongest run of the year is February to April. October is the quietest month: hot and slow-paced, and still good for green season and quiet and local.
Long-run climate normals for Koh Samui. Month ratings compare months within Koh Samui only — they are not a ranking of Koh Samui against other destinations, and they are not a forecast for a specific year.
Conditions on this page are recalculated from the latest forecast every time it is opened, for the current date in the location's own time zone. Showing .
| Best month | March — Beach days, Swimming, Reliable sunshine |
| Best 3-month window | February–April |
| Quietest month | October — Hot and slow-paced |
| Driest month | March — 21mm |
| Wettest month | November — 129mm |
| Warmest / coolest | August 33°C / April 30°C |
| Seasonality | Strongly seasonal — the months feel like different places |
| Annual rainfall | 900mm over roughly 96 rain days |
October gets roughly 514% more precipitation than March — 129mm against 21mm. That difference, more than temperature, is what changes how a day here feels.
Daytime highs only move 3°C across the whole year (30–33°C), so timing matters far less here than rainfall does.
March is the driest month at 21mm across roughly 2 wet days, while November peaks at 129mm.
April is almost as good as March, but usually quieter and cheaper. If your dates are flexible, it is the easier trip.
Koh Samui changes character completely through the year — March and October are effectively two different destinations. Pick the month that matches what you want to do, not the highest-rated one.
Ratings compare months within Koh Samui, not against destinations worldwide: five stars means the best time to be here, not that Koh Samui beats anywhere else. Tags describe what the conditions actually suit.
| Month | Rating | High / Low | Precipitation | Wet days | Sun | Daylight | Best for |
|---|---|---|---|---|---|---|---|
| January | ★★★★☆ | 31°C / 25°C | 75mm | 8 | 9h | 11.5h | Beach days · Swimming · Reliable sunshine |
| February | ★★★★★ | 30°C / 24°C | 39mm | 4 | 11h | 11.7h | Beach days · Swimming · Reliable sunshine |
| March | ★★★★★ | 30°C / 24°C | 21mm | 2 | 12h | 12h | Beach days · Swimming · Reliable sunshine |
| April | ★★★★★ | 30°C / 24°C | 21mm | 2 | 12h | 12.2h | Beach days · Swimming · Reliable sunshine |
| May | ★★★★★ | 31°C / 25°C | 39mm | 4 | 11h | 12.4h | Beach days · Swimming · Reliable sunshine |
| June | ★★★★☆ | 32°C / 26°C | 57mm | 6 | 10h | 12.6h | Beach days · Swimming · Reliable sunshine |
| July | ★★★☆☆ | 32°C / 27°C | 75mm | 8 | 9h | 12.5h | Beach days · Swimming · Reliable sunshine |
| August | ★★★☆☆ | 33°C / 28°C | 93mm | 10 | 8h | 12.3h | Beach days · Swimming · Quiet and local |
| September | ★★☆☆☆ | 33°C / 28°C | 111mm | 12 | 7h | 12h | Beach days · Swimming · Quiet and local |
| October | ★★☆☆☆ | 33°C / 28°C | 129mm | 14 | 6h | 11.8h | Green season · Quiet and local |
| November | ★★☆☆☆ | 32°C / 27°C | 129mm | 14 | 6h | 11.6h | Green season · Quiet and local |
| December | ★★☆☆☆ | 32°C / 26°C | 111mm | 12 | 7h | 11.4h | Beach days · Swimming · Quiet and local |
| You are planning | Pick | Why |
|---|---|---|
| Sun & beach days | March | 12h daily sunshine, 30°C highs and only 2 rain days. |
| City walking & sightseeing | March | 30°C highs with 12h of daylight — long days without heat fatigue. |
| Photography & light | April | 12h of sun and 12.2h daylight give the widest window for golden-hour work. |
| Value & fewer crowds | May | Scores 75/100 — close to peak conditions but outside the busiest window. |
| Cooler-weather travel | March | 30°C highs and 24°C nights suit anyone who dislikes heat. |
Each month in Koh Samui is described from long-run climate normals and then rated relative to the other eleven months in the same city. A five-star January in a cold destination means January is one of the best times to be there — not that it beats a Mediterranean summer.
| Factor | Weight | What it measures |
|---|---|---|
| Temperature | Described | Average daytime high and overnight low for the month, shown as measured rather than judged. |
| Precipitation | Described | Monthly millimetres and wet-day count, labelled as snow or rain/snow where temperatures make that the likely phase. |
| Sunshine & daylight | Described | Average daily sunshine hours and astronomical daylight length at mid-month, from the city’s latitude. |
| “Best for” tags | Derived | Applied only when the conditions genuinely support the activity — snow depth-friendly cold for skiing, 13–24°C and low rain risk for hiking, dark evenings at high latitude for aurora. A month with few strong use cases gets fewer tags rather than padded ones. |
| Star rating | Relative | Ranks the month against the other eleven months in the same city. Never a comparison between cities. |
Figures are long-run climate averages, not a forecast for a specific year. This city has no published month-by-month normals on file, so monthly temperatures are interpolated from its summer and winter averages and rainfall is modelled from rain-day frequency.
March is the best all-round month in Koh Samui: 30°C highs, 21mm of precipitation and 12 hours of daylight, which suits beach days, swimming and reliable sunshine. The strongest three-month window is February to April.
October — 33°C highs, 129mm of precipitation over roughly 14 days and 11.8 hours of daylight. It is the cheapest and least crowded time to go, and it still works for green season and quiet and local.
March is the driest month at 21mm over about 2 rain days, against 129mm in November. Across the year Koh Samui records around 900mm.
Yes, but the months are genuinely different trips. March suits beach days, swimming and reliable sunshine, while October suits green season and quiet and local. Pick the month that matches what you want to do.
Daylight ranges from 11.4 hours in December to 12.6 hours in June, calculated from the city's latitude.