Surat Thani is Thailand's largest southern province, renowned as the gateway to world-famous Gulf islands including Koh Samui, Koh Phangan, and Koh Tao. The province combines pristine island beaches, the ancient rainforest of Khao Sok National Park, and the emerald waters of Cheow Lan Lake, making it one of Thailand's most diverse destinations.
Surat Thani province has a tropical monsoon climate with two distinct seasons: the dry season (December to April) and the wet season (May to November). The province receives significant annual rainfall from two monsoon systems — the southwest monsoon brings rain from May to October, while the northeast monsoon delivers heavy rains from October to December. The islands generally experience slightly different weather patterns, with Koh Samui's rainy season peaking in November.
Best time to visit
Best: December to April
Best Reason: The dry northeast monsoon season brings clear skies, calm seas, and sunny weather across Surat Thani province. January and February are peak beach season with the warmest, clearest water for diving and snorkeling.
Peak Season: December to February
Avoid: October and November
Avoid Reason: October and November see the heaviest rainfall from the northeast monsoon, with significant flooding risk in Surat Thani City and rough seas making ferry crossings uncomfortable or cancelled.
Month-by-month weather
Typical conditions throughout the year.
January
27°C/81°F average
Peak dry season — sunny days, calm seas, and excellent visibility for diving and snorkeling. Busy and expensive on the islands.
February
28°C/82°F average
Arguably the finest month for beaches — warm, clear, and calm. Whale sharks sometimes spotted at Sail Rock. Peak tourist crowds and prices.
March
29°C/84°F average
Still dry and warm. Transitioning to slightly lower crowds as post-peak season begins. Good for all activities.
April
30°C/86°F average
Hot and mostly sunny. Songkran (April 13-15) is a highlight. Small chance of afternoon showers towards month end.
May
30°C/86°F average
Transitional month — increasing afternoon thunderstorms but often still sunny mornings. Lower crowds and good value.
June
29°C/84°F average
Southwest monsoon brings regular rain, often in afternoon bursts. Mornings still sunny. Great value month for island visits.
July
29°C/84°F average
Regular tropical rainstorms but usually with sunny intervals. Khao Sok is especially lush. Good month for diving on Koh Tao.
August
29°C/84°F average
Similar to July — regular rain especially on the mainland but islands receive less. Excellent value accommodation rates.
September
28°C/82°F average
Heavy rainfall on the mainland. Koh Tao and Koh Phangan can still be decent. Risk of rough seas.
October
27°C/81°F average
The wettest month for most of the province. Flooding risk in Surat Thani City. Ferries sometimes cancelled. Not recommended for island hopping.
November
27°C/81°F average
Northeast monsoon arrives — Koh Samui's wettest month with heavy daily rains. Koh Tao and Koh Phangan are better but also rainy.
December
27°C/81°F average
Early December can still see some rain but conditions improve rapidly. Christmas and New Year see peak prices and crowds. Great holiday atmosphere.
The seasons
What to expect in each part of the year.
Spring
Months: Mar-May
The transitional period from dry to wet season. March and April are excellent with sunshine and warm seas. May brings increasing humidity and occasional afternoon thunderstorms.
Summer
Months: Jun-Aug
The southwest monsoon brings regular rain, particularly in the afternoons. Mornings are often sunny. The islands receive less rain than the mainland, making them still quite pleasant. Jungle at Khao Sok is lushest during this period.
Fall
Months: Sep-Nov
September and October mark the peak wet season. November brings the northeast monsoon's heaviest rains specifically to Koh Samui and the east coast. Khao Sok is very rainy. Rough seas can cancel ferries.
Winter
Months: Dec-Feb
The northeast monsoon delivers dry, sunny conditions to the mainland and west coast islands. December-February is peak season with the best weather for beach holidays and diving. Koh Samui sees occasional short rain showers but mostly sunshine.
Crowds & peak times
When to expect tourists and when to avoid them.
- High Season
- December to February (Christmas/New Year peak), plus July-August (European summer)
- Shoulder Season
- March-April and May-June — good weather and moderate crowds
- Low Season
- September-November — lowest prices but challenging weather
Major events & festivals
Time your visit around what matters.
Songkran (Thai New Year)
National water festival celebrated throughout the province with street water fights and temple merit-making
Full Moon Party
Monthly beach party on Haad Rin, Koh Phangan — dates vary each month based on lunar calendar
Chak Phra Festival
Surat Thani's unique festival with boat processions on the Tapee River — one of Thailand's most distinctive regional festivals
Loy Krathong
Festival of lights with floating lantern releases on rivers and beaches throughout the province
New Year Countdown
Major celebrations on Chaweng Beach, Koh Samui and throughout the islands