Rainy Season in Koh Samui — When It Is & What to Expect
Koh Samui has a distinct rainy season covering April to December, when roughly 1534mm of rain falls — the bulk of the annual total. The wettest month is November (323.1mm over about 26 rainy days). Outside these months rainfall drops sharply, which is why the best time to visit is All year.
Koh Samui — Monthly Rainfall
Average monthly rainfall in millimetres, calculated from 2020–2023 data. Highlighted bars mark the rainy season.
Rainfall in Koh Samui month by month
| Month | Rain | Rainy days | High | Rating |
|---|---|---|---|---|
| January | 43.1mm | 14 | 28.5°C | 10/10 |
| February | 58.2mm | 14 | 29.0°C | 10/10 |
| March | 36.5mm | 9 | 30.5°C | 10/10 |
| April Wet | 106.9mm | 16 | 31.1°C | 9/10 |
| May Wet | 134.5mm | 20 | 31.0°C | 9/10 |
| June Wet | 102.4mm | 18 | 30.6°C | 9/10 |
| July Wet | 149.9mm | 22 | 30.0°C | 9/10 |
| August Wet | 114.2mm | 21 | 30.4°C | 9/10 |
| September Wet | 196.8mm | 22 | 29.2°C | 9/10 |
| October Wet | 244.4mm | 28 | 28.5°C | 8/10 |
| November Wet | 323.1mm | 26 | 28.1°C | 8/10 |
| December Wet | 161.7mm | 19 | 27.9°C | 9/10 |
Should you visit Koh Samui during rainy season?
It can still work. Rain in the wet season often falls in short, intense bursts rather than all-day washouts, prices are lower and crowds thinner. But expect high humidity, disrupted boat trips and island transfers, and the occasional flooded street — November in particular is best avoided.
Best time to avoid the rain
The driest, most comfortable window is All year — see the full best time to visit Koh Samui guide for the month-by-month breakdown.
Frequently Asked Questions
When is rainy season in Koh Samui?
Rainy season in Koh Samui runs April to December, peaking in November with 323.1mm of rain.
What is the wettest month in Koh Samui?
November — averaging 323.1mm of rain over roughly 26 rainy days.
Can you visit Koh Samui during rainy season?
It can still work. Rain in the wet season often falls in short, intense bursts rather than all-day washouts, prices are lower and crowds thinner. But expect high humidity, disrupted boat trips and island transfers, and the occasional flooded street — November in particular is best avoided.
When is the dry season in Koh Samui?
The driest, most comfortable months are All year — see the best time to visit Koh Samui guide.
Travelling in the wet season anyway?
Pack right for it — the full checklist is on our sister site.
Koh Samui packing list →Compare Hertz, Avis, Budget, Sixt and 800+ rental companies — book now, pay at pickup.
Compare car hire prices → Affiliate link — we earn a commission at no extra cost to youAs an Amazon Associate we earn from qualifying purchases. Links below are affiliate links.
Check your Koh Samui packing list at 247PackingList for a full wet-season checklist. For country facts, see our Thailand guide at 247CountryInfo.
Wet season essentials for Koh Samui
Compact travel umbrella
Windproof, fits in a daypack, dries fast — non-negotiable in monsoon season.
Check Price →Packable waterproof jacket
Light enough for the humidity, sealed enough for the downpours.
Check Price →Dry bag
Keeps phones, passports and cameras dry through boat trips and sudden storms.
Check Price →More wet-season travel gear
Quick-dry travel clothing
Lightweight and quick-drying — ideal for high-humidity wet seasons.
Check Price →Last updated:
Climate data sourced from Open-Meteo (open source, open data licence). Monthly averages calculated from 2020–2023 historical data. Weather can be unpredictable — always check a live forecast before travelling.