Best Time to Dive Koh Tao: Month-by-Month Guide

Featured image: Visions of Domino, CC BY 2.0, via Wikimedia Commons.

The short answer: which months to pick

Aim for January to June if you want flat seas and visibility of 20–30 m, as local operators report it. April and May add the best whale shark odds. July to September brings fewer people, and October to December brings lower accommodation rates and a second whale shark window. Boats go out every day of the year, so fixed dates still work. Match your pick to the kind of diver you are.

• First Open Water student: May to September, when quieter shops suit courses.
• Certified fun diver: January to May for the clearest water.
• Whale shark chaser: March to May or October to November, with no guarantee.
• Crowd-averse diver: September and October.
• Fixed-dates traveler: come anyway and ask about the shop's bad-weather plan.

Can you dive Koh Tao year-round?

Yes. Local operators report water between 28°C (82°F) and 31°C (88°F) in every month, and boats sail 365 days a year. A 3 mm suit is enough, and many divers skip a suit entirely. Our water temperature guide covers suit choice in detail. The Gulf of Thailand is naturally sheltered, so even the rainy months rarely stop diving. If you are still weighing the island itself, read whether Koh Tao is good for diving.

Koh Tao diving conditions by month

Figures below are operator-reported approximations, not guarantees. Visibility swings day to day and site to site. Prices and hours checked November 2026. For rainfall and wind outlooks, use the Thai Meteorological Department. Water in March sits near 29°C (84°F), and May peaks near 31°C (88°F).

Where the seasons and sources disagree

Published seasons do not line up, so treat the edges of each season as soft. June, September and October are the months to book with flexibility. Three points of conflict matter most.

• Whale shark windows: one Koh Tao operator says March to May and October to November. A regional liveaboard broker says March to April and September to October.
• End of the dry season: the operator runs it to June. A blogger with 100+ Koh Tao dives puts it at December to May.
• Start of wind: the blogger reports windy weather from July or August. Island friends now call June "windy June", though she did not dive it herself.

When to see whale sharks

Operators report sightings year-round, with peaks in March to May and again in October to November. Sail Rock and Chumphon Pinnacle are the sites named most often. Chumphon sits about 45 minutes from Koh Tao by boat. Odds stay uncertain, though. One blogger logged 100+ dives on the island and never saw one. Treat peaks as tendencies, not promises, and never build a whole trip around one animal. Our whale shark guide covers sightings in depth. Turtles and schooling fish give you other reasons to dive in any month, as the marine life overview shows.

Best month to dive Koh Tao by diver type

Your goal matters more than the calendar. Use this grid, then adjust for your own dates.

Bad-weather days: what actually happens

Rough water on the west side usually means a change of site, not a cancelled day. One operator says it switches to east-coast sites such as Hin Wong Pinnacle and Tanote Bay, which are naturally protected from the prevailing winds. That operator also reports 28 sites around the island and says it reschedules at no charge in the rare case no outing is possible. Sail Rock is the exception. It sits far out, and most shops visit only about once a week. In November and December the sea can be too rough for it. Rougher months are not shown to make dives riskier, but know your emergency plan. See our hyperbaric chamber guide, and read Divers Alert Network guidance on insurance. Ask each shop before you pay:

• What is the bad-weather plan for west-side sites?
• What is the reschedule or refund policy for a lost day?
• How large are the boats, and how many divers per guide?
• For courses, what is the class size in your travel month?

Mistakes to avoid when timing a dive trip

Four errors cause most disappointment.

• Booking only for whale sharks. Sightings are never promised.
• Assuming rainy season means no diving. Boats still run in October to December.
• Skipping the bad-weather question. It decides what happens on a windy morning.
• Booking a Sail Rock day with no spare day in the schedule.

Crowds, booking lead time and cost timing

Operators flag December to January and July to August as the busiest weeks. March to May also fills with divers chasing whale sharks. Book those periods early. September and October see significantly fewer visitors. One Koh Tao fun-dive catamaran listed prices starting at ฿2,000 in 2026. No source gives a verified month-by-month price swing, so see current dive costs and compare quotes. Shop choice matters too, and the dive resort guide helps with it. Night dives run in any season, as the night dive guide explains.

Koh Tao versus the Andaman side by month

The Andaman Sea is usually strongest from November to April. The Gulf, including Koh Tao, is often the better choice from May to September. A trip in those summer months suits Koh Tao better than the west coast. Remote Andaman sites such as the Similan Islands are liveaboard territory, so read about a Koh Tao Liveaboard: Options, Alternatives & When to Go if you want distant sites from here.