Koh Tao is Thailand's top diving island. This month-by-month guide covers diving conditions, weather, visibility, and the best time to visit for every type of traveller.
Koh Tao — "Turtle Island" — is Thailand's premier diving destination. The island has trained more divers than almost anywhere else in the world, with warm clear water, abundant marine life, and dive schools to suit every budget.
Koh Tao's Two Seasons
Dry season (March–September): Gulf of Thailand's east coast is calm and clear. Best diving visibility, most reliable weather.
Wet season (October–February): Rougher seas, some dive site closures. East coast sites remain mostly accessible.
Key fact: Koh Tao's wet season is opposite to Phuket — when Phuket is wet, Koh Tao is often dry.
Month-by-Month Breakdown
January–February: Good Conditions
Weather: 27–32°C | Diving: Good, 15–25m visibility | Rates: Shoulder
Solid months — worst of wet season has passed. Whale sharks occasionally spotted at Chumphon Pinnacle.
March–May: Excellent — Best Value
Weather: 28–34°C, minimal rain | Diving: Excellent, 20–30m | Rates: Shoulder-to-high
Best overall conditions. Whale shark sightings increase. Pre-peak crowds. Arguably the best time to visit.
June–August: Peak Season
Weather: 28–33°C, calm | Diving: Excellent | Rates: Peak
European summer fills the island. Whale shark encounters most frequent. Book dive courses in advance.
September–October: Transition
Weather: Increasing rain | Diving: Good (Sep), variable (Oct) | Rates: Dropping
September still good. October sees rougher conditions — east coast sites remain diveable.
November–December: Wet Season
Weather: Regular rain, rough seas | Diving: Variable | Rates: Lowest
November is wettest. East coast sites often still accessible. Best value for flexible travellers.
Best Dive Sites
Chumphon Pinnacle: Top site — whale sharks, giant grouper, barracuda. Best June–September.
Sail Rock: Chimney dive between Koh Tao and Koh Phangan. Whale sharks year-round.
Southwest Pinnacle: Excellent coral and fish life. All levels.
White Rock: Shallow, ideal for beginners and snorkellers.
Diving Courses
PADI Open Water courses cost 9,000–12,000 THB — significantly cheaper than most destinations. Top schools: Big Blue Diving, Crystal Dive, Ban's Diving Resort.
Getting There
- From Koh Samui: 2-hour high-speed ferry
- From Surat Thani: 3-hour high-speed or 6-hour night ferry
Verdict
Best overall: March–May (excellent diving, pre-peak, good value)
Best for whale sharks: June–September
Best value: November–February
Avoid: October–November if you want guaranteed diving
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