May 31 sees frequent showers in Koh Samui. Historical data shows a 40% chance of rain, so pack accordingly. Temperatures average 28°C. Koh Samui is currently in its most popular travel window, meaning vibrant crowds and premium pricing.
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Essential Travel Info for Koh Samui
Currency
THB
฿ Thai baht
Language
Thai
Driving
Left side
Safety
Moderate Safety
GPI: 2.098
Koh Samui Weather Forecast for May 31
"Warm & Sunny. Expect average highs of 27.9°C. 40% chance of rain."
What to Wear in Koh Samui in May
Based on historical data for May 31, Koh Samui typically experiences temperatures between 24.3°C and 27.9°C. We recommend packing t-shirt, light clothing, umbrella to stay comfortable. With a 40% chance of rain, keeping a raincoat or umbrella handy is a smart move.
Complete Packing Guide
Weekly breakdown & essential items for Koh Samui
Smart Suitcase
- T-Shirt
- Light Clothing
- Umbrella
Average High
27.9°C
Daytime Peak
Average Low
24.3°C
Nighttime Low
Feels Like
31.6°C
🔥 Feels warmer
Rain Chance
40%
Avg 2.9mm if it rains
Cloud Cover
84%
Light drizzle
Pressure
N/A
Low volatility
Koh Samui Weather Conditions & UV Index
Weather Confidence
30-year variance analysis
Based on 10 years of data
🎯 This date historically delivers consistent weather 84% of the time. Safe to plan outdoor activities with confidence.
Sun Exposure
UV Index & Safety Guide
Protection Needed
SPF 30 recommended
05:00 - 10:00
16:00 - 18:00
Type I-II
🔴 17 min to burn
Type III-IV
🟡 26 min to burn
Type V-VI
🟢 43 min to burn
UV estimate based on latitude, season & cloud cover. Actual UV may vary.
Outdoor Comfort
How pleasant is it outside?
Dew Point
23.7°C
Humid/Sticky
Heat Index
31.6°C
Feels hotter
😐 Best outdoor time:
Morning hours (before 11 AM)
Marine Conditions
Marine Life
No special warnings. Enjoy the swim!
Swim Index
✅ Excellent Swimming Conditions
Travel & Logistics Insights
Local Calendar
Business Day
Standard hours in Thailand
Flight Traffic
High
92/100 pressure index
Health Advisory
Required
2 vaccines • View Details →
Landing Slots
~49
Daily arrival options (inc. codeshare)
Sunrise, Sunset & Wind in Koh Samui
Daylight & Sun
Solar Elevation Cycle
🌅 Sunrise
05:59
☀️ Noon
12:19
🌇 Sunset
18:38
⏱️ Daylight
12h 38m
Wind Speed
19.3 km/h
Gentle breeze
Sunshine
9.9 hrs
Direct Sun (Cloud-free)
Humidity
78%
Humid / Damp
Travel Intelligence
Exclusive flight analytics & health data for Koh Samui
Smart Flight Estimator
Airport-to-Airport Logistics
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Travel Health & Safety in Koh Samui
Travel Comfort Index
Real-time tourism conditions
Weather Quality
⛅ Good
Tourist Crowds
🟡 Busy
Price Level
💰💰💰 Expensive
Health & Wellbeing
Meteo-Health Forecast
Stable conditions. Low risk of headaches.
Weather unlikely to affect joint pain.
Moderate fish activity expected.
Air quality is acceptable. Sensitive individuals should limit prolonged outdoor exertion.
Regional Safety Profile
Seismic Activity
Zero seismic activity detected in 30 years.
Typhoon Risk
Year-round risk present
Travel Alert: This region has elevated natural risks. We recommend registering with your embassy and keeping emergency numbers handy.
"According to 30YearWeather's analysis of 30 years of NASA satellite data, Koh Samui on May 31 averages 27.9°C with a 40% precipitation probability. Wedding/Outdoor Event Score: 82/100."
— Source: 30YearWeather.com|Data: NASA POWER (1991-2021)|View Methodology
Koh Samui Weather History (2010–2024)
Temperature History
Hall of Fame
Records from last 10 years
Better Alternatives Nearby
Consider these dates within ±7 days
May 25
27.9°C • 27% rain
Score
90
May 24
27.8°C • 31% rain
Score
88
May 26
27.9°C • 33% rain
Score
88
💡 Moving your event by a few days could significantly improve weather conditions
Compare Other Cities
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📍 Is Koh Samui Worth Visiting on May 31?
Planning a trip to Koh Samui on May 31? Our historical weather analysis based on 30 years of NASA satellite data shows that this time of year typically offers vibrant summer conditions averaging 27.9°C with a 40% historical precipitation risk.
✈️ Travel Logistics: Approximately 49 landing slots available daily during this period, indicating manageable crowd levels.
💉 Health Advisory: 11 vaccinations are recommended for Thailand, including COVID-19.
🌊 Coastal Conditions: Water temperature averages 31.4°C (hot soup). Wave conditions are generally lake-like with heights around 0.29m.
📊 Historical Extremes: The hottest May 31 recorded in the last 30 years saw temperatures hit 30.2°C in 2025, while the coldest dropped to 22.6°C in 2018.