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.

Gulf of Thailand · Seasons & weather

Best time to visit Surat Thani

Almost nobody comes to Surat Thani for Surat Thani. The season that matters here is the one that decides whether the boats run.

The season that actually matters

Surat Thani is a river city and a transport hub, not a beach. Most travellers arrive on a night train or a flight, sleep once, and leave on a boat. So the weather question is not really about sunbathing; it is about whether the crossing to Koh Samui, Koh Phangan or Koh Tao goes ahead, and whether the road to Khao Sok is passable.

The calendar is the southern Gulf one: dry from February to September, wet from October to December, with November and December the heaviest. That is the opposite of the Andaman coast, which is why a trip that combines Khao Sok with Samui has to be planned in two halves.

Transport

Tickets & connections

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In short

Surat Thani seasons

February–September: dry, calm sea, ferries on schedule
October–December: the rainy season, November and December heaviest
Ferry risk: cancellations at short notice in November and December
Chak Phra festival: October, end of Buddhist Lent
Same calendar as Koh Samui, the opposite of Khao Sok

February to September, the easy stretch

February to April is the driest and hottest part of the year, with a flat sea and ferries running to schedule. May to September stays largely dry on this coast while the Andaman side is under its monsoon, and it is the cheapest good weather you will find in southern Thailand.

This is also the reliable window for the Donsak crossings. Boats leave from Donsak pier, about an hour and a half east of town, and in these months the timetable is the timetable.

Good to know

Planning around the weather

Leave a spare day between your last ferry and your flight home in November and December.
Donsak pier is about ninety minutes east of town — count that into the timetable, not out of it.
Khao Sok is two hours west and runs on the Andaman calendar: wet when the coast here is dry.
The night train from Bangkok arrives before dawn, timed for the morning boats.

Cheow Lan lake in Khao Sok, west of Surat Thani

October to December, and the boats

The rain builds through October and peaks in November and December. Surat Thani province floods in some years, roads through the lowlands go slow, and the sea between the mainland and the islands gets rough enough that crossings are cancelled at short notice. If your flight home is the day after your ferry, this is the season to leave a day of slack.

October brings Chak Phra, the city's own festival at the end of Buddhist Lent, when decorated Buddha images are pulled through the streets and along the river. It is the one time of year Surat Thani is worth stopping in for its own sake.

Month by month

January	Showery at the start, drying out, quiet
February	Dry and calm — the good season begins
March	Hot and dry, the flattest sea of the year
April	Hottest month, Songkran mid-month, still dry
May	Hot with short showers, low prices
June	Warm and mostly dry — excellent value
July	Warm, brief showers, boats on schedule
August	Warm and largely dry, the European summer pick
September	Still good, showers slowly increasing
October	The rains arrive; Chak Phra festival in town
November	Wettest month — rough crossings, possible flooding
December	Wet and windy, improving towards New Year

Frequently asked questions

When is the best time to visit Surat Thani?

February to September. February to April is the driest and calmest, and June to September stays largely dry here while the Andaman coast is in its monsoon.

When is the rainy season in Surat Thani?

October to December, with November and December the heaviest. The province floods in some years, and ferry crossings to the islands are cancelled at short notice.

Can the ferries to Koh Samui be cancelled?

Yes, mostly in November and December when the sea gets rough. If you have a flight to catch, leave a day of slack between the crossing and the airport.

Does Khao Sok have the same weather as Surat Thani?

No. Khao Sok sits on the other side of the divide and follows the Andaman calendar, so it is wettest from May to October, when the coast at Surat Thani is mostly dry.

Travel guides

More guides to Surat Thani and the way on to the Gulf islands.

Part of the guides for

Surat Thani

Surat Thani