Thailand Koh Samui Weather in May — Climate Guide
May in Koh Samui is moderate
Koh Samui Weather in May — Quick Answer
As of 2026- Avg temp
- 32° / 25°
- Rainfall
- 150mm · 14 days
- Crowds
- Moderate
As of 2026, Koh Samui in May averages a high of 32°C and low of 25°C with 150mm of rain over about 14 days. Start of the long wet season, but still warm and often sunny between showers. Around 32°C/25°C, humid. Light clothing, swimwear, SPF 50+, and a light rain layer for the increasing afternoon showers. Sea ~30°C.
May is moderate for Koh Samui.
May marks the start of Koh Samui's long wet season, but it's a gentle, good-value start — averaging 32°C/25°C with moderate rainfall (around 150mm), often in passing afternoon or evening showers rather than all-day rain.
Mornings are frequently sunny, and the rain tends to come in short bursts, so beaches and many boat trips still work — it's a far cry from the heavy October-December monsoon. Prices drop and crowds thin after the April peak, making it a strong shoulder-season value window.
Travel score
Koh Samui May Weather Stats
Avg High
32°C
Avg Low
25°C
Rainy Days
14
150mm total
Sunshine
7h
Daily avg
Humidity
80%
muggy
UV Index
11
Extreme
Wind
11 km/h
Gusts 22
Sea Temp
30°C
Avg water temp
Crowds
Moderate
At attractions
May Sunrise & Sunset
Air Quality
PM2.5
14 μg/m³
PM10
26 μg/m³
Status
good
Feels-Like Temperature & Wind
Feels like
Daytime
38°C
Nighttime
27°C
Humidity and wind affect how the actual temperature feels.
Wind
11 km/h
Max gust 22 km/h
Activities Recommended for May
May Travel Pros & Cons
Pros
- Shoulder-season value — lower prices, quieter beaches
- Often sunny mornings with short showers
- Lush, green landscapes
- Better than rainy Andaman coast (Phuket/Krabi) now
Cons
- Wet season begins — afternoon showers increase
- Less guaranteed boat-trip conditions
- High humidity
- Occasional heavier rainy days
May Events & Festivals
- Wet season begins — afternoon/evening showers increase
- Shoulder-season value — quieter beaches and lower prices
- Often sunny mornings with passing showers
- Greener, lush landscapes
Koh Samui in May — Full Picture
May marks the start of Koh Samui's long wet season, but it's a gentle, good-value start — averaging 32°C/25°C with moderate rainfall (around 150mm), often in passing afternoon or evening showers rather than all-day rain.
Mornings are frequently sunny, and the rain tends to come in short bursts, so beaches and many boat trips still work — it's a far cry from the heavy October-December monsoon. Prices drop and crowds thin after the April peak, making it a strong shoulder-season value window.
The landscape turns lush and green, and the heat is offset a little by the showers. Seas are mostly fine, though conditions are less guaranteed than the dry months — check before booking boat trips.
This is where the Gulf timing really pays off: as Phuket and Krabi on the Andaman coast head into their soggy season, Samui is only easing into a mild wet phase, with a notably drier spell coming in June-August.
The sea is warm (~30°C). UV stays high (11) even with more cloud — keep up the SPF.
What to Wear & What to Pack
Start of the long wet season, but still warm and often sunny between showers. Around 32°C/25°C, humid. Light clothing, swimwear, SPF 50+, and a light rain layer for the increasing afternoon showers. Sea ~30°C.
Packing Checklist
Seasonal Weather Overview
Spring (Mar·Apr·May)
Current31.7°C
25°C
10/mo
Summer (Jun·Jul·Aug)
32°C
25°C
13.3/mo
Autumn (Sep·Oct·Nov)
30°C
24.3°C
18/mo
Winter (Dec·Jan·Feb)
29°C
24°C
12.3/mo
Koh Samui Monthly Weather Comparison
| Month | High | Low | Rain | Sun | Humid | UV | Crowd | Price |
|---|---|---|---|---|---|---|---|---|
| 29° | 24° | 14d·180mm | 6.5h | 82% | 10 | Very busy | Peak | |
| February (Best) | 30° | 24° | 6d·60mm | 8h | 78% | 11 | Very busy | Peak |
| March (Best) | 31° | 25° | 7d·75mm | 8.5h | 78% | 12 | Busy | Peak |
| 32° | 25° | 9d·100mm | 8.5h | 78% | 12 | Busy | Peak | |
| 32° | 25° | 14d·150mm | 7h | 80% | 11 | Moderate | Shoulder | |
| 32° | 25° | 13d·110mm | 7.5h | 78% | 11 | Busy | Shoulder | |
| 32° | 25° | 13d·110mm | 7.5h | 78% | 11 | Very busy | Peak | |
| 32° | 25° | 14d·110mm | 7h | 78% | 11 | Very busy | Peak | |
| 31° | 25° | 15d·150mm | 6h | 80% | 10 | Moderate | Shoulder | |
| 30° | 24° | 19d·290mm | 5h | 84% | 9 | Quiet | Low season | |
| 29° | 24° | 20d·340mm | 4.5h | 85% | 9 | Quiet | Low season | |
| 28° | 24° | 17d·230mm | 5h | 84% | 9 | Very busy | Peak |
View Other Months
Koh Samui May Hotel Picks
Frequently Asked Questions
Is May a good time to visit Koh Samui?
Koh Samui in May is moderate. Tourist crowds are moderate and flight/hotel prices are shoulder.
What's the average temperature in Koh Samui in May?
Koh Samui May averages a high of 32°C and a low of 25°C.
Does it rain much in Koh Samui in May?
Koh Samui May averages 150mm of rainfall over about 14 rainy days.
What should I wear in Koh Samui in May?
Start of the long wet season, but still warm and often sunny between showers. Around 32°C/25°C, humid. Light clothing, swimwear, SPF 50+, and a light rain layer for the increasing afternoon showers. Sea ~30°C.
What time are sunrise and sunset in Koh Samui in May?
Koh Samui May sunrise is 06:00 and sunset is 18:30, with 12h 30min of daylight.
What's the air quality like in Koh Samui in May?
Koh Samui May air quality (AQI) averages 38, rated Good. PM2.5 averages 14μg/m³.
What activities are recommended in Koh Samui in May?
In May, Koh Samui is great for Beach days between showers, Ang Thong/Koh Tao (check conditions), Island temple & waterfall loop.
Is May peak season in Koh Samui?
Koh Samui May crowds are moderate and prices are shoulder. You can travel relatively comfortably without long queues.
Best Months to Visit Koh Samui
View Other Months
Planning a May trip to Koh Samui?
You've checked the weather — next come the budget and the route.
Why you can trust weather guide
Based in Chiang Mai for 8+ years, with 30+ countries visited across Southeast Asia, Japan, and Europe. Every detail in this guide is primary-source verified as of April 2026, with prices auto-refreshed via live exchange rate APIs. This isn't AI-generated boilerplate — it's written from the perspective of someone who has actually been there.