Weather and Best Time in Koh Samui and Koh Tao
Part of the Koh Samui and Koh Tao travel guide — see every topic in All Koh Samui and Koh Tao Guides.
The weather on Koh Samui, Koh Phangan and Koh Tao is different from much of Thailand. These islands are on the Gulf of Thailand side. Their main rainy season comes late in the year, from about October to December. On the Andaman coast, around Phuket and Krabi, the main rain comes from about May to October. This means the Gulf islands are a good choice when the Andaman side is wet.
The dry months
The best weather on the Gulf islands is usually from about January to April. Days are sunny, the sea is calm and the water is clear. From about February, it is a very good time for diving on Koh Tao. These months are also the busiest, especially around the New Year and in February, so book rooms and flights early. March and April are the hottest months. Plan beach time for the morning and late afternoon, and rest in the shade at midday. Easter and other school holidays in many countries also fall in this period.
The middle of the year
From about May to September the weather is still good on the Gulf islands. There are some showers, but they are often short. This is a smart time to visit, because it is the rainy season on the Andaman coast. The Gulf islands are a good choice for a beach trip in July and August, during school holidays in many countries. Wind can make some beaches a little choppy at times. On Koh Tao, this is also a good time for whale sharks. Rooms are often easier to find than in the peak months.
The monsoon, October to December
The heaviest rain usually falls from about mid-October to early December. November is often the wettest month. There can be strong winds, heavy rain for days, and rough seas. Ferries may be cancelled, and Ang Thong Marine Park usually closes from about 1 November to 15 December. Flooding can close some roads for a short time. Prices are lower in these months, and there are still sunny days. If you visit in this season, keep your plans flexible and leave an extra day before any flight home. Many visitors choose a hotel with a pool and good indoor space for rainy days.
Gulf or Andaman?
Thailand has two coasts with beaches. The Gulf side includes Samui, Phangan and Tao. The Andaman side includes Phuket, Krabi and the Phi Phi Islands. Their rainy seasons fall at different times. A simple rule: from about May to September, choose the Gulf. From about November to April, the Andaman side is usually better, but the Gulf is also good from about January. In the dry months both coasts can be good, so you can visit both on one trip. Flights link Samui with Phuket and Krabi, so it is easy to add one beach from each coast.
Temperature and what to pack
It is warm all year on the Gulf islands. Daytime temperatures are usually around 28 to 34 degrees C. The sea is warm enough to swim in at any time. Pack light, loose clothes, a hat, sunglasses and reef-safe sun cream. A light rain jacket is useful, even in the dry months. In the monsoon months, bring a dry bag for your phone on boats. Cover your shoulders and knees when you visit temples or local villages. Drink plenty of water, because the heat and humidity make you tired quickly.
Weather and Best Time at a glance
| Best time | About January to April for calm seas and sun |
|---|---|
| Good value | About May to September; dry when the Andaman side is wet |
| Rainy season | About mid-October to early December; November often wettest |
| Ang Thong closure | Usually about 1 November to 15 December |
| Temperature | Warm all year, about 28 to 34 degrees C by day |