Things to Do in Koh Tao in September

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Stay in Koh Tao in September

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September on Koh Tao is an awkward month to plan for. The Gulf of Thailand misses the worst of the southwest monsoon that soaks Phuket and Krabi, which keeps this island far more usable than the Andaman coast, but showers still turn up most afternoons. Daytime highs hover around 27.8°C (82°F), and nights barely cool to 25.9°C (79°F), so the air on Sairee Beach at 10pm feels much like it did at noon.

The European summer crowd is gone by the first week of September, and Mae Haad pier gets noticeably quieter when the morning catamarans come in from Chumphon. Dive shops in Chalok Baan Kao and Sairee run smaller groups in September, sometimes two or three students per instructor. The crossing from the mainland, though, can be rough on west-wind days. The 90-minute run from Chumphon is not one you want to make with a queasy stomach.

The real problem arrives in October and November, when the northeast monsoon brings the island's wettest weeks. September is the last month before that. You get warm water, mostly diveable sites and shoulder-season quiet, and you trade them for grey skies on roughly three days in four. Many of those rainy days bring a single downpour of under an hour, and the smell of wet frangipani afterwards is half the charm.

Why visit in September

Once the August European holiday rush ends, group sizes at dive schools in Sairee and Chalok Baan Kao drop sharply, and Open Water courses often run with two or three students per instructor.
Whale sharks turn up at Chumphon Pinnacle and Sail Rock more often in the September to October window than in midsummer, though no sighting is ever guaranteed.
Tanote Bay and Ao Leuk on the east coast are sheltered from the southwest wind, so their snorkelling water stays calm and clear even when Sairee Beach is choppy.
Koh Nang Yuan's sandbar viewpoint draws a fraction of its high-season day-trip crowd, especially on weekday mornings before 10am.

Worth knowing

Rain falls on around 23 days of the month, and when an afternoon storm builds and stalls, longtail trips to Mango Bay and Koh Nang Yuan can shut down with little warning.
The Chumphon to Mae Haad catamaran crossing can be rough during southwest-wind spells, and occasional cancellations leave travellers stranded for a night on the mainland.
Humidity near 81% means laundry, towels and dive gear stay damp for days in Sairee guesthouses without air conditioning.
A handful of smaller bars and restaurants in Sairee Village close for staff holidays in late September, ahead of the October to November monsoon.

Best for

Think twice if

Weather measured 28° / 26°C 192mm rain · 23 rainy days · 81% humidity rains perceptibly ~3.7h/day · 68% of mornings dry

Crowds low

Pack Quick-dry shorts and synthetic T-shirts, a packable rain shell, reef-safe sunscreen for the bright breaks between showers, and sandals with grip for the slick concrete roads between Mae Haad and Sairee.

Warm, sticky, and changeable is a fair summary. The five-year average puts rainfall at 192mm (7.6 in) spread over about 23 rainy days, with humidity around 81%, and most of that arrives as short afternoon or evening bursts rather than all-day grey, though a two-day blow off the southwest monsoon rolls through once or twice a month. Sea temperature sits near 29°C (84°F), so a 3mm shorty is plenty for diving. September looks mild next to November's 336mm (13.2 in), though it is wetter than August's 145mm (5.7 in).

Seasonal caution

Southwest monsoon swells can make the west-coast beaches at Sairee and Mae Haad choppy, and ferry operators occasionally cancel Chumphon crossings with a few hours' notice.
The steep concrete tracks down to Tanote Bay and Ao Leuk turn slippery after rain, and scooter crashes on those hills are the island's most common tourist injury.

Year-round climate

Averages from the last 5 years.

Monthly climate averages for Koh Tao
Month	Avg high (°C)	Avg low (°C)	Rainfall (mm)
Jan	27	25	20
Feb	27	25	76
Mar	28	26	33
Apr	29	27	80
May	29	27	189
Jun	29	27	120
Jul	29	26	172
Aug	28	26	145
Sep	28	26	192
Oct	28	25	275
Nov	28	25	336
Dec	27	25	135

Best things to do in September

Dive Chumphon Pinnacle and Sail Rock

diving

These two deep granite pinnacles are the island's headline dive sites, and Sail Rock sits roughly halfway to Koh Phangan, with a vertical swim-through called the Chimney.

September and October produce the most frequent whale shark reports of the year, and the boats carry far fewer divers than they do in April.

Booking tipBook the Sail Rock trip 2-3 days ahead, because schools won't run it unless they have enough divers to fill the longer boat ride.

Snorkel Tanote Bay and Ao Leuk

snorkelling

Coral and boulder reefs sit within 50m (164 ft) of the sand in both east-coast bays, and blacktip reef sharks are sometimes spotted at Shark Bay, a short way south.

When the southwest wind roughs up Sairee, the east coast stays calm, and these bays regularly offer better visibility in September than the famous west side.

Booking tipAfter rain, take a songthaew taxi down the steep road rather than a rented scooter.

Open Water course in Chalok Baan Kao

diving

The four-day PADI or SSI entry course runs in the shallow, sheltered training bays around Chalok Baan Kao and Japanese Gardens at Koh Nang Yuan.

Low-season classes run two or three students per instructor, against six or more in July and August.

Booking tipReach out to two or three schools a week before you arrive and ask what their actual class size will be on your start date.

Freedive training at Tanote

freediving

Freediving schools run buoy lines in Tanote Bay's deeper water for depth training, working toward 20m (66 ft) and beyond.

During southwest-wind weeks, the flat east-coast water makes line training far more comfortable than in November, when the northeast monsoon hits that side.

Early hike to John-Suwan Viewpoint

hiking

A short, steep trail above Chalok Baan Kao climbs to a granite boulder that looks out over both Chalok and Shark Bay.

The driest window in September is usually before 9am, and the rain-washed air gives the sharpest views of the year.

Booking tipBring cash for the small landowner's entry fee at the trailhead.

Quiet morning at Koh Nang Yuan

day trip

Three linked islets joined by a sandbar sit off the northwest tip of Koh Tao, and a steep boardwalk climbs to the island's most photographed viewpoint.

Day-trip boats are scarce in September, so the sandbar is often near-empty before 10am.

Booking tipTake the first taxi boat from Sairee and check the forecast, since boats stop running when westerly swell builds.

What to eat in September

In season: fruit

Longkong
This southern Thai cousin of langsat peaks from late August into October. The pale, sweet-sour clusters arrive in piles on the ferry from Chumphon and Surat Thani growers.
Rambutan
The southern rambutan season tails off in September, so the last hairy red bunches at Mae Haad fruit stalls tend to be cheap and very sweet.

On menus now

Kaeng som pla
Chalok Baan Kao's local kitchens lean on this sour, turmeric-yellow southern fish curry on rainy evenings, and the sharp tamarind heat clears a damp head fast.

Festival food

Khanom for Sart Thai
Surat Thani province marks the Tenth Lunar Month festival with khanom la (lacy rice-flour sheets), khanom ba, and khanom kong, and during festival week you'll find them stacked as offerings and sold at Mae Haad.
Mooncakes
In the weeks before the full moon of the eighth Chinese lunar month, mooncakes for the Mid-Autumn Festival turn up in 7-Eleven and Thai-Chinese bakeries across the island.

Regular events in September

Sart Thai (Tenth Lunar Month Festival)Free

Surat Thani province, which includes Koh Tao, makes merit for ancestral spirits with food offerings and khanom stacks at temples. On the island it is quieter than on the mainland.

15th day of the waning moon of the tenth lunar month, usually mid-to-late September or early October

Mid-Autumn FestivalFree

Thai-Chinese families light lanterns and share mooncakes, and small offerings appear at shrines around Mae Haad.

25 September in 2026

Full Moon Party at Haad Rin, Koh Phangan

The monthly beach party on the neighbouring island pulls some backpackers off Koh Tao for a night, and dedicated party boats leave from Mae Haad.

On or near the September full moon, around 26 September in 2026

Mahidol DayFree

The Thai observance honouring Prince Mahidol, the father of modern Thai medicine, is marked in hospitals and schools but is not a public holiday.

24 September

Best places this September

Tanote Bay
beach
This east-coast cove has boulders, a jumping rock and coral close to shore, and stays sheltered during southwest-wind weeks.
Tanote
Ao Leuk
beach
A small, deep-sided bay with some of the island's best shore snorkelling, reached down a steep concrete road.
Ao Leuk
Koh Nang Yuan
island
Three islets joined by a sandbar off the northwest coast, with the viewpoint climb at the far end.
Sairee
John-Suwan Viewpoint
viewpoint
A granite outcrop above the south coast overlooking Chalok Baan Kao and Shark Bay.
Chalok Baan Kao
Chumphon Pinnacle
dive site
A deep granite pinnacle about 11km (7 miles) northwest of Koh Nang Yuan, known for batfish, barracuda and occasional whale sharks.
offshore
Sairee Beach
beach
The island's longest west-coast beach at about 1.7km (1 mile). Its sunset strip empties out noticeably after August.
Sairee
Hin Wong Bay
bay
A rocky, remote east-coast bay with clear water in calm spells and almost no crowd in September.
Hin Wong
Mae Haad pier
market area
The arrival point for every ferry, with fruit stalls that are the easiest place to buy longkong in season.
Mae Haad

Your packing checklist

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Packable rain shellAfternoon storms usually pass within an hour, and a light shell weighs less than a poncho on a scooter. Shop
Motion sickness tabletsTake them 30 minutes before the Chumphon catamaran, since southwest swell can make the crossing lurch. Shop
Dry bag, 10-20 litresLongtails to Mango Bay and Koh Nang Yuan throw spray, and sudden showers soak phones on the ride back. Shop
Silica gel packs or zip bagsHumidity keeps cameras and passports damp in fan rooms, and mould can start on leather within a week. Shop
Reef-safe sunscreenUV stays fierce in the bright gaps between September clouds, and several dive schools ask guests to avoid oxybenzone. Shop
Grippy sandalsWet concrete roads down to Tanote and Ao Leuk turn slick, and flip-flops cause a lot of scrapes. Shop
3mm shorty wetsuitWater near 29°C (84°F) feels cool on a third dive of the day, and your own suit dries faster than a shared rental. Shop
Mosquito repellent with DEET or picaridinStanding rainwater breeds mosquitoes, and dengue cases across southern Thailand tend to rise through the wet months. Shop

Insider tips

If the wind is out of the southwest, skip Sairee for snorkelling and head to Ao Leuk or Tanote, and if it swings northeast late in the month, reverse that plan.
Divers in Chalok Baan Kao often ask to swap to a Sail Rock trip once a whale shark report comes in, so tell your school you want a call if one is sighted.
The first taxi boat to Koh Nang Yuan beats the tour groups by about 90 minutes, and the viewpoint boardwalk is dry enough before the afternoon storms.
Long-stay room deals are rarely advertised online, so ask in person at Sairee guesthouses for a monthly rate, since late September is when owners most want occupancy before the wet season.
Mae Haad fruit sellers usually lower longkong prices in the late afternoon, when the day's ferry stock needs to move before it bruises.

Avoid these mistakes

Booking the last afternoon catamaran from Chumphon on the day of an international flight home. Weather cancellations do happen this month, so leave a buffer night.
Renting a scooter to ride down to Tanote or Ao Leuk in the rain. Those hills are the island's crash hotspot, and a songthaew costs less than a clinic visit.
Writing off the whole island because the forecast shows rain icons every day. Most September showers last under an hour, so plan boats and hikes for the mornings.

Practical tips for September

Check the ferry schedule the evening before any mainland crossing, as operators post weather cancellations late. Dive schools may shift west-coast sites to the east side at short notice, so keep plans flexible. ATMs cluster in Mae Haad and Sairee, and the smaller viewpoints and beach access roads charge cash-only landowner fees. Temples expect covered shoulders and knees during Sart Thai merit-making, and tipping dive crews at the end of a course is customary but optional. Some Sairee Village bars shorten hours or close for a week in late September, so check ahead before walking across the island. Solo travellers can weigh the island's 7.6/10 solo-safety score (see the TTDI Solo-Safety Index) alongside the scooter warning above.

FAQ

Is September a good time to visit Koh Tao?

It is a fair month, not a great one. The island stays warm and mostly diveable, crowds thin after August, and rates fall. Rain will find you on most days, so September suits divers and budget travellers better than those chasing sun. February to April is far more reliable.

Is it rainy on Koh Tao in September?

Yes, fairly often, though rarely all day. Showers tend to arrive in the afternoon or evening and clear within an hour. The heavy wet season hits in October and November, which see roughly one and a half to nearly twice September's rainfall.

Can you dive on Koh Tao in September?

Yes. Water temperatures stay warm, most sites run normally, and whale sharks are reported at Chumphon Pinnacle and Sail Rock more often in this window. Schools may swap west-coast sites for sheltered east-coast ones when the southwest wind picks up.

Is Koh Tao crowded in September?

No. After the European summer holidays end in the first week of the month, Sairee Beach and Koh Nang Yuan feel noticeably emptier, and dive classes shrink to small groups.

Do ferries to Koh Tao get cancelled in September?

Occasionally. Southwest swell can make the Chumphon crossing rough, and operators sometimes cancel sailings with short notice. Build a spare night into your plans before any flight home.