December 18 is generally a great time to visit Koh Samui. While there is a slight chance of rain (39%), showers are usually brief. Expect comfortable 25°C weather. 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 December 18
"Mild & Comfortable. Expect average highs of 24.8°C. 39% chance of rain."
What to Wear in Koh Samui in December
Based on historical data for December 18, Koh Samui typically experiences temperatures between 22.6°C and 24.8°C. We recommend packing t-shirt, light clothing, umbrella to stay comfortable. With a 39% 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
24.8°C
Daytime Peak
Average Low
22.6°C
Nighttime Low
Feels Like
25.7°C
☀️ Feels accurate
Rain Chance
39%
Avg 2.8mm if it rains
Cloud Cover
69%
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 75% of the time. Safe to plan outdoor activities with confidence.
Sun Exposure
UV Index & Safety Guide
Protection Needed
SPF 15 for extended outdoor time
UV estimate based on latitude, season & cloud cover. Actual UV may vary.
Outdoor Comfort
How pleasant is it outside?
Dew Point
20.9°C
Humid/Sticky
Heat Stress
Low
No heat warning
🙂 Best outdoor time:
Any time during daylight hours
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
85/100 pressure index
Health Advisory
Required
2 vaccines • View Details →
Landing Slots
~45
Daily arrival options (inc. codeshare)
Sunrise, Sunset & Wind in Koh Samui
Daylight & Sun
Solar Elevation Cycle
🌅 Sunrise
06:30
☀️ Noon
12:17
🌇 Sunset
18:04
⏱️ Daylight
11h 34m
Wind Speed
22.7 km/h
Moderate wind
Sunshine
9.5 hrs
Direct Sun (Cloud-free)
Humidity
79%
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 December 18 averages 24.8°C with a 39% precipitation probability. Wedding/Outdoor Event Score: 86/100."
— 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
December 24
24.8°C • 18% rain
Score
98
December 25
24.9°C • 20% rain
Score
97
December 22
24.8°C • 19% rain
Score
96
💡 Moving your event by a few days could significantly improve weather conditions
Compare Other Cities
Same date (December 18) in other destinations
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📍 Is Koh Samui Worth Visiting on December 18?
Planning a trip to Koh Samui on December 18? Our historical weather analysis based on 30 years of NASA satellite data shows that this time of year is characterized by pleasant mild weather averaging 24.8°C with a 39% historical precipitation risk.
✈️ Travel Logistics: Approximately 45 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 28.6°C (tropical bath). Wave conditions are generally fun waves with heights around 0.83m.
📊 Historical Extremes: The hottest December 18 recorded in the last 30 years saw temperatures hit 26.6°C in 2024, while the coldest dropped to 20.7°C in 2022.