Best Season to Visit Koh Samui: Weather, Rain & Things to Know
Its wet season runs opposite to Phuket and Krabi
The best time to visit Koh Samui is December to April, when the island sees its driest, sunniest weather and calmest seas. Unlike Phuket and Krabi on the Andaman coast, Koh Samui faces the Gulf of Thailand, so its wet season follows the northeast monsoon in October and November rather than the southwest monsoon that soaks most of the country from May to October.
Why Samui's weather runs opposite to the rest of Thailand
Month-by-month weather
| Month | Weather | Rain | Rating |
|---|---|---|---|
| January | Warm and dry, ~26°C, ~7 hours of sun daily | Low | Best |
| February | Dry, minimal rain, ~8 hours of sun, sea ~27°C | Low | Best |
| March | Warm and dry, 26–31°C, blue skies | Very low | Excellent |
| April | Hottest month, Songkran mid-month | Low | Very good |
| May | Warm and sunny, noticeably quieter | Medium | Good |
| June | Warm, mostly dry, low crowds | Low-medium | Good |
| July | Warm and mostly dry | Low | Good |
| August | Warm, occasional short showers | Low | Good |
| September | Quietest month, more humid | Medium | OK |
| October | Rain increasing, seas rougher | Very high | Avoid |
| November | Wettest month, ~320mm average rainfall | Extremely high | Avoid |
| December | Drying out, sunny by late month | Low | Best (if budget allows) |
Sourced from travelguidestip.com's 2026 month-by-month weather guide, tourinkohsamui.com's 2026 monthly breakdown, insidesamui.com's complete season guide, and traveloka.com's Singapore-focused Koh Samui weather guide.
The single best month, according to most sources
Comes up repeatedly as the single best month
February comes up repeatedly as the single best month to visit. The remnants of the January monsoon have faded, the island stays dry with roughly 8 hours of sunshine a day, and temperatures haven't yet climbed into the more intense heat of March and April. March is a close second, with one detailed local guide specifically calling it "the best ratio of weather quality to value" across the whole calendar year.
An honest note on the July to September shoulder season
Sources genuinely differ here. Several guides describe June through August as "surprisingly good," warm, mostly dry, with calm seas and noticeably lower prices than peak season. Others rate this stretch more cautiously, particularly September, as rainfall starts building toward the October and November peak. Realistically, expect a mixed bag: more good days than bad, but pack for occasional short showers if you're travelling in this window.
Why November is worth actively avoiding
More than double the rainfall of any other month
Practical tips
Book December through March well in advance if calm seas and reliable sunshine matter most to your trip, this is peak season, and both flights and hotels fill up early.
Target February or March specifically if you want the best combination of weather and value, both come up repeatedly as the strongest overall months.
Consider May, June, or July if you want good weather without peak-season pricing or crowds, this shoulder window offers a solid trade-off.
Avoid booking Ang Thong Marine Park tours for early November through late December, the park is typically closed for the monsoon during this exact window.
Common mistakes to avoid
- Assuming Koh Samui follows the same rainy season as Phuket or Krabi. The islands face different coasts, and applying Andaman-coast timing to a Samui trip can lead to booking during the wrong month entirely.
- Booking a November trip based on general "Thailand rainy season" assumptions rather than checking Samui's own specific pattern. November is genuinely the worst month on the island, not a safe middle ground.
- Planning an Ang Thong Marine Park day trip without checking the seasonal closure dates first. The park closes annually for roughly seven weeks around the wettest period.
- Overlooking July through September as "just the rainy season" without checking the specifics. This stretch is meaningfully different from October and November, and can offer good value if you're flexible about the occasional shower.