Koh Samui in August: Weather, Sea and What's On

August is Koh Samui's so-called "Big Season": not a rain month in any real sense, but noticeably busier than June or July because of European school holidays. Weather and sea temperature stay just as good, but accommodation and tours are worth booking a little earlier than in the months before.

At a glance

Weather in August

Climatically, August barely differs from July: similar temperatures, and on average even slightly less rain. Showers tend to stay short and localised, usually in the afternoon, with the rest of the day staying sunny. The east coast (Chaweng, Lamai, Choeng Mon) generally stays calm, while the west coast sees occasional extra wind from the south-west monsoon, which mainly affects the Andaman coast at this time of year. The biggest difference from July isn't the weather – it's the crowds: European summer holidays bring a lot more families to the island.

What you can do in August — and what you can't

Boat and snorkelling tours run as usual in August, and Ang Thong Marine Park is open as normal. Because the island is busier, it's worth booking early for popular dates and family cabins. If a short burst of heavy rain hits, an indoor alternative like a cooking class is a better bet than rescheduling a boat tour at short notice.

The more affordable Ang Thong big-boat option suits families well: pick-up between 07:15 and 08:00, departing from Nathon in the west of the island, then around 90 minutes by boat from 08:30 to Mae Koh island and its Emerald Lagoon, followed by the viewpoint on Koh Wua Talap. Breakfast, buffet lunch, soft drinks and snorkelling gear are included, kayaking for an extra fee, and the park entrance fee (300 THB adults, 150 THB children) is paid locally:

from 1,250 THBAngthong Marine Park Full-Day Big Boat Economy Tour★★★★★4.76 from 361 reviews

For a late-afternoon option, the Pig Island sunset tour fits well: pick-up between 13:00 and 14:30, departing from the south, snorkelling at Koh Tan, a visit to the woolly pigs on Koh Madsum, and the return crossing around 17:45 at sunset, including dinner on the beach. The 50 THB island entrance fee is payable separately:

from 1,550 THBSunset snorkeling tour pig island Koh Mudsum & Koh Tan★★★★★4.73 from 22 reviews

On a rainy afternoon, the Thai cooking class is a reliable backup: pick-up around 08:00 or 13:00 in the south of the island, four hours in an open-air kitchen with a sea view, cooking a 5-course menu from your own choices, including the meal itself:

from 1,750 THBUnique Activity Thai cooking class 4 hours Koh Samui★★★★★4.88 from 52 reviews

Festivals and events in August

The key date in August is 12 August 2026: Queen Mother Sirikit's Birthday, also observed as Thai Mother's Day. It's a national public holiday marked with garlands, jasmine flowers for mothers, and blue decorations (her colour, as someone born on a Friday) – unlike the Buddhist holy days in July, this day carries no alcohol sales ban. As a public holiday, expect slightly more domestic visitors around this date.

Fruit in season

Durian season is tailing off in August but the fruit is still widely available, as is mangosteen in its final weeks. Rambutan and longan are both in the middle of their main season, which runs through September. Papaya, jackfruit, dragon fruit, guava and coconut remain available year-round. For the full seasonal calendar and customs rules on taking fruit home, see our Top 10 fruits in Thailand.

Frequently asked questions

Does it rain a lot on Koh Samui in August?

No — with around 100 mm over about 11 days, August is actually one of the drier months of the year, well below the levels seen in the real rainy season from October to December.

Is August a good time to visit Koh Samui?

Yes, weather-wise August is almost identical to July. The difference is the crowds: because of European summer holidays ("Big Season"), flights, hotels and popular tours are in higher demand and cost a bit more than in the months before.

Why is Koh Samui busier in August?

Because it's peak summer holiday time across much of Europe. The weather barely changes from July, but the number of families with children visiting does.

Is there an alcohol sales ban on Koh Samui in August?

No. The 12 August public holiday (Queen Mother's Birthday/Mother's Day) is not a Buddhist holy day and doesn't trigger a nationwide sales ban, unlike Asalha Bucha or Khao Phansa in July.

For the months either side, see Koh Samui in July and Koh Samui in September. The full climate table and an explanation of the Gulf-side rainy season are in Koh Samui weather and the truth about the rainy season, and an overview of every month is in The best time to visit Koh Samui.