Koh Lanta Water Temperature by Month (and Diving)

Featured image: Marcin Konsek, CC BY-SA 4.0, via Wikimedia Commons.

Quick answer: how warm is the sea in Koh Lanta?

Sea temperature around Koh Lanta stays between 29°C and 32°C in every month. SkyLand's long-term averages give an annual mean of 30.1°C. May is warmest at about 32°C. January is coldest at about 29°C, with February and December close behind. A 3°C spread across twelve months is smaller than the swing in sea state between a calm April and a rough September. SkyLand counts any water above 18°C as swimming season, so every month qualifies on temperature alone. Our Koh Lanta diving season guide holds the full calendar, and this page stays focused on the numbers.

Koh Lanta water temperature by month

Averages run from 29°C in January to 32°C in May. Figures below are approximate long-term sea surface values from SkyLand, not a forecast. Sea state notes come from local month-by-month reports and describe tendencies, not guarantees.

Warm water, but not always good water

Conditions swing far more than temperature does. November to April brings calm seas and good visibility. Rain returns from May, and the Andaman Sea turns choppier. Monsoon season runs June to October, when winds shift from easterlies to westerlies. In July, rough seas make ferry crossings and boat trips less reliable. Swimming on the west coast beaches is sometimes limited that month. August brings stronger waves and reduced underwater visibility. September is typically the roughest month, with boat trips limited. October starts to calm, and diving reopens slowly. Where you swim also matters. The west coast has sandy beaches between rocky outcrops, while the east coast is mostly mangroves. Ban Saladan on the north end of the island is the ferry hub, and Ko Lanta National Marine Park occupies the south end.

Do you need a wetsuit?

At 29–32°C, nobody needs thick neoprene for comfort at the surface. A rash guard or a 3 mm shorty covers most single-dive days. Divers who chill easily often step up to a full 3 mm suit. Three or four dives in one day also pull heat from the body, even in 29°C water. January is the coolest month, so that is when a longer suit pays off most. Our Koh Lanta diving overview covers what a typical dive day involves. Fun divers can read how a fun dive day is usually structured. For general diver health guidance, see Divers Alert Network. Ask about suit hire when you book, since sizes and stock vary by operator.

Temperature at the dive sites

Surface averages are not dive-depth figures. Published month-by-month temperatures for the offshore pinnacles are scarce. Treat the 29–32°C range as a surface guide and ask your operator what the water felt like on recent dives. Currents and depth can change how cold a dive feels. Hin Daeng Diving from Koh Lanta: Who It Suits and How to Go and Hin Muang Dive Site: Koh Lanta Trip, Depth & Who Can Dive are exposed offshore sites, so sea state and boat access matter more there than a degree of temperature. Koh Haa from Koh Lanta: Diving, Snorkeling and Day Trips is another offshore group where swell decides whether trips run. Our Koh Lanta dive site guide compares them side by side.

Best months by goal

Pick the month by the conditions you want, not by the thermometer. Each goal below maps to a different part of the year.

• Calm and clear: November to April, with December, January and February the most dependable for visibility.
• Budget and quiet: May to October brings fewer tourists and lower prices, but also rain and limited boat trips.
• Shoulder-season gamble: October, when the sea calms and diving reopens, or May, when seas start to get choppier.
• Skip July to September if you are a nervous swimmer, since rough seas and ferry delays are common.
• Skip August and September if you are a photographer who needs clear water.
• First-time divers on a short stay should avoid the rough months, because a cancelled boat can cost the whole trip.

Planning checks before you book

Check live wave height and wind on the morning you plan to dive, because forecasts change daily. Ask any operator about its cancellation policy, especially for the two roughest months, August and September. Ask what site it would switch to if seas are rough. Browse the Koh Lanta dive centers to compare options. Beginners can see how PADI courses on Koh Lanta are run. Official course standards are published by PADI. If you want a named operator to start with, see Phoenix Divers. Short-notice trips depend on boat schedules and sea state more than on a single degree of temperature.