When to Visit Koh Samui

Temperatures sit at a high of 29°C (84°F) and a low of 24°C (75°F), with rainfall around 127mm (5 inches). Showers tend to be short-lived and the sea generally stays calm, making this one of the better months on Koh Samui despite being far from the driest. This is peak season and the beaches reflect that, with full resorts and lively beach bars.

The driest month of the year, averaging just 64mm (2.5 inches), with highs of 29°C (84°F). The Gulf tends to be at its most settled, and boat connections to the surrounding islands run smoothly. Expect beaches to be busy, though the island isn't yet overwhelmed.

Rainfall ticks up slightly to 117mm (4.6 inches) but temperatures remain mild at a high of 30°C (86°F) and a low of 25°C (77°F). Koh Samui in March has a pleasant balance, enough warmth for the beach, occasional afternoon showers that cool things down, and crowds that are noticeable but not oppressive.

The hottest month, with highs reaching 31°C (89°F) and lows at 26°C (79°F), and rainfall staying relatively moderate at 84mm (3.3 inches). The Songkran water festival in mid-April adds a cultural layer worth factoring into plans, and the island gets busy with domestic Thai travelers during that period as well.

Temperatures peak at 32°C (90°F) and rainfall climbs to 132mm (5.2 inches), marking the shift into the wetter season. The rains on Koh Samui in May tend to arrive in afternoon bursts, leaving mornings clear for beach time. Crowds thin as prices begin to soften noticeably.

Similar conditions to May, with 32°C (90°F) highs and 135mm (5.3 inches) of rainfall, technically the wettest month outside the October-to-December increase, though the rains remain intermittent rather than relentless. The island is quieter now, and accommodation offers more flexibility on rates.

Rainfall eases slightly to 117mm (4.6 inches) and temperatures hold at 32°C (90°F). Despite being school holiday season in much of Europe, Koh Samui sees fewer visitors during July than its Andaman competitors, making it a quieter option for families who want the Gulf side.

The driest month of the wet season, averaging 102mm (4.0 inches) of rainfall, with highs at 32°C (90°F). August here can feel like a pleasant surprise, as the weather is often more cooperative than the off-season reputation suggests, and the beaches are uncrowded.

Temperatures ease to a high of 31°C (89°F) and a low of 24°C (76°F), with 117mm (4.6 inches) of rainfall. The sea can be choppier on the north and east coasts as the northeast monsoon begins to build, and some boat trips become less reliable. Value-seekers tend to do well here.

The shift is pronounced. Rainfall jumps to 295mm (11.6 inches), starting Koh Samui's serious wet season. Temperatures settle back to a high of 30°C (87°F). Some beach clubs and restaurants on the north coast begin reduced hours. Ferry connections can be disrupted during storms. The island's interior, its waterfalls, temples, and jungle trails, often looks extraordinary after heavy rains.

The wettest month on Koh Samui by a significant margin, averaging 444mm (17.5 inches) of rainfall. Temperatures sit at a high of 29°C (85°F) and a low of 24°C (75°F). Extended grey skies and persistent rain are possible. Gulf swells can be rough enough to affect swimming on all coasts. Travelers with beach-focused itineraries find this month the most challenging on the island.

Rainfall remains high at 264mm (10.4 inches) though it begins easing toward month's end. Temperatures stay at a high of 29°C (84°F) and a low of 24°C (75°F). The island stirs with Christmas and New Year visitors. They accept the weather trade-off for a festive atmosphere. The final week typically sees a sharp increase in both arrivals and prices.