When is the best time for diving on Koh Tao?

Roughly March to September, when seas are calm and visibility at its best. Diving runs year-round, but October to December brings wind, rain and reduced visibility.

When is the rainy season on Koh Tao?

October to December, peaking in November. Like the rest of the Gulf, Koh Tao stays largely dry through the European summer months.

Can ferries to Koh Tao be cancelled?

Yes — in the November–December monsoon, rough seas occasionally halt crossings from Chumphon and Surat Thani for a day or two. Build slack into travel plans in those months.

When can you see whale sharks at Koh Tao?

Sightings happen year-round and are never guaranteed. Many divers report clusters of sightings in the settled months around March–May and again around September–October.

Best Time to Visit Koh Chang: Season and Rain

The eastern Gulf runs on the Andaman calendar

This catches people out. Koh Chang is in the Gulf of Thailand, but it does not follow Koh Samui's weather: its rain arrives with the south-west monsoon from May to October, the same months as Phuket, and its dry season is November to April.

So if you are choosing between Koh Chang and Koh Samui for a trip in October, they are not equivalent. Koh Chang is at the tail of its wet season, and Samui is heading into its own. The two Gulf islands are on genuinely different calendars.

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In short

Koh Chang seasons

November–April: dry season, calm sea, everything open
May–October: heavy rain, half price, much of the south closed
Best value: November and late April
Busiest and dearest: Christmas to mid-January
Same calendar as Phuket, not the same as Koh Samui

The dry season, month by month

November is the reopening: the jungle is at its greenest, the waterfalls still have water, and prices have not yet climbed. December to February is the peak — the most reliable weather of the year, cool enough at night to sleep without air conditioning, and busy at Christmas and New Year.

March and April are hot, dry and quieter than the peak, with April bringing both the year's highest temperatures and Songkran, the national water festival. The sea is at its calmest and clearest through this whole stretch, which is when the snorkelling trips to the outer islands are worth doing.

Good to know

Planning around the weather

Do not assume Koh Chang and Koh Samui share a season — they do not.
Boat trips to the outer islands are most reliable from December to March.
The waterfalls are best just after the rains, from October to December.
Roads get slick in the wet, and the hills here are steep — take extra care on a scooter.

The rainy season is really rainy

Koh Chang gets more rain than most Thai islands, and July to September is the heaviest of it. Rain still tends to come in bursts rather than all day, but the mountain catches weather and the jungle stays wet. On the upside, the waterfalls are at their most impressive and the island is beautifully green.

Practically, a lot closes. Lonely Beach and the southern end lose many of their bars and restaurants, some resorts shut entirely, and boat trips to the outer islands are cancelled when the sea is up. The car ferries keep running in almost all weather, so getting there is rarely the problem — but check that your hotel and its kitchen are open.

Month by month

January	Dry, cool nights, calm sea — peak season
February	Hot, dry and reliable, the best diving visibility
March	Hot and dry, quieter than the peak
April	Hottest month, Songkran mid-month, season ending
May	Rains begin, prices drop, first closures
June	Wet and green, warm rain in bursts
July	Heavy rain, many boat trips cancelled
August	One of the wettest months, waterfalls at their fullest
September	Wettest and quietest — much of the south is shut
October	Rain easing, the island starts reopening
November	Green, open and calm — the best value month
December	Dry and cool, prices climb towards Christmas

Frequently asked questions

When is the rainy season on Koh Chang?

May to October, with July to September the heaviest. It is one of the wetter Thai islands, because the mountain in the middle catches the weather.

Does Koh Chang have the same season as Koh Samui?

No. Koh Chang is dry from November to April, the same as Phuket. Koh Samui runs on a different calendar and is at its wettest around November.

Does Koh Chang close in low season?

Partly. The northern beaches stay open, but much of Lonely Beach and the southern end closes from about May to October.

When is Koh Chang cheapest?

June to October, when room rates fall sharply. Just check that your hotel and the restaurants near it are still open.

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Koh Chang

Best time to visit Koh Chang