Koh Samui Rainy Season: November and December vs the Andaman Coast

The Koh Samui rainy season is the opposite of most of Thailand. While Bangkok, Chiang Mai and Phuket dry out in November, the Gulf islands get their heaviest rain of the year as the northeast monsoon pushes in from the sea. That does not mean Samui is a bad choice for a late-year trip, but it does change what you can plan. This guide explains what November and December are usually like on Samui, which trips are affected, and when the Andaman coast is the better pick.

Photo: Vyacheslav Argenberg / Wikimedia Commons, CC BY 4.0

How the Koh Samui rainy season works

Thailand's southern peninsula has two coasts with different weather.

• The Andaman coast (Phuket, Krabi, Koh Lanta, Koh Lipe) gets rain from the southwest monsoon, roughly May to October. From November it enters its dry season.
• The Gulf coast (Koh Samui, Koh Phangan, Koh Tao) is partly sheltered from that monsoon, so it stays fairly dry in the middle of the year. Its main wet season comes later, from about October to December, when the northeast monsoon brings rain and wind.

According to the Thai Meteorological Department, November is usually the wettest month on the Gulf side of the south. December is often still wet in the first half, then improves. January and February are usually sunnier.

The pattern varies from year to year. Some Novembers have long dry spells, and some Decembers stay grey. Treat it as a probability, not a rule.

What November and December are like on the ground

Rain comes in bursts. Rather than all-day drizzle, you often get heavy showers, sometimes for a few hours, with dry gaps in between. A run of several wet days in a row is also possible when a low-pressure system passes.

The sea is rougher. On days with strong northeast winds, the east-facing beaches such as Chaweng and Lamai get bigger waves. Swimming can be unsafe when red flags are up. Beaches on the west and south coasts, such as Lipa Noi, are often calmer.

Boats can be disrupted. When waves are high, the authorities may warn small boats to stay in port. Ferries and speedboats between Samui, Koh Phangan and Koh Tao, and from the mainland at Donsak, can be delayed or cancelled. Build in a spare day before a flight.

It stays warm. Temperatures remain comfortable, and humidity is high. Pack light rain gear rather than warm clothes.

What closes or changes

Ang Thong National Marine Park is closed to visitors from 1 November to 15 December 2026 for the monsoon season, according to the Department of National Parks. It reopens on 16 December. The popular day trip by boat to the park's islands, lagoon and viewpoint is not possible during the closure, and in the weeks after reopening it can still be called off on rough days.

Snorkelling and diving trips from Samui to Koh Tao and nearby reefs run less often, and visibility drops after heavy rain.

Some beach bars and small resorts use the quiet weeks for repairs and close for a short period.

What still works well in the rain:

• The Big Buddha and Wat Plai Laem on the north coast, which are quick visits between showers
• Cafés, spas, cooking classes and Thai massage
• The Fisherman's Village night market in Bophut on Fridays, if the weather holds
• Driving to the waterfalls, which have more water in this season, though paths can be slippery

Photo: Fabio Achilli from Milano, Italy / Wikimedia Commons, CC BY 2.0

Samui or the Andaman coast?

If your main goal is beach days and island boat trips, the Andaman coast is usually the safer choice in November and early December.

Pick the Andaman side (Phuket, Krabi, Lanta, Lipe) if:

• You travel in November or the first half of December
• You want snorkelling or island-hopping trips, which depend on calm seas
• You have a short trip with no spare days

Samui still makes sense if:

• You go from late December, when the weather usually improves
• You are mainly there for a resort, a spa or a family stay, and rain breaks are fine
• You find good hotel rates and are happy to keep plans flexible

If you want both, a common pattern is to start on the Andaman coast in December and move to Samui in January. Flights link Samui with Bangkok, Phuket and Krabi via several routes, but they are not cheap, so compare times and prices before you commit.

When to switch to the Gulf

From about mid-January to April, the Gulf islands are usually at their best: dry, calm seas and clear water for Ang Thong, Koh Tao and Koh Nang Yuan trips. This is also when the Andaman coast starts to get hotter and busier, so Samui becomes the stronger choice.

The Gulf's quieter months, from May to September, are another good window for Samui while the Andaman side is wet.

A flexible 4-day plan for December

Day 1: arrival and the north coast

Fly in and check in near Bophut or Bangrak, where the north coast is a little more sheltered in this season. Visit the Big Buddha and Wat Plai Laem in the late afternoon, then walk Fisherman's Village.

Day 2: beach morning, inland afternoon

Spend the morning on the beach if it is dry. If it rains, drive inland to Na Muang waterfall, or book a cooking class.

Day 3: Ang Thong or a south coast day

If you are on Samui after 16 December and the sea is calm, book the Ang Thong boat trip. Otherwise, explore the quieter south and west coasts, with the Hin Ta Hin Yai rocks at Lamai and a sunset on the west side.

Day 4: slow morning and departure

Keep your last day light so a boat or weather delay does not affect your flight.

Our 4 days in Koh Samui sample trip gives a full plan for a drier month, and you can reorder the days in RoamerPlanner when the forecast changes. For the Andaman alternative, see our 3 days in Phuket trip or 3 days in Krabi trip.

Planning tips for the wet weeks

• Check the forecast daily from the Thai Meteorological Department, and follow any warnings for the Gulf of Thailand.
• Book boats that can be changed, and do not plan a ferry on the same day as an international flight.
• Choose your beach with the wind in mind. In northeast winds, the west and north coasts are often calmer than Chaweng and Lamai.
• Get travel insurance that covers weather delays.
• Drive carefully. Roads are slippery after rain, and many accidents on the island involve rented motorbikes.

For a wider look at the season, our guide to Thailand in December compares each region.

Quick FAQ

When is the rainy season on Koh Samui? Usually from about October to December, with November the wettest month. January to April is usually drier.

Is Koh Samui worth visiting in December? It can be, especially in the second half of the month. Expect some rain and plan flexible days.

Is Ang Thong Marine Park open in November? No. In 2026 it is closed from 1 November to 15 December and reopens on 16 December.

Sources, checked 4 November 2026: Thai Meteorological Department climate information and seasonal outlook for southern Thailand; Department of National Parks announcement on the 2026 Mu Ko Ang Thong National Park closure (1 November to 15 December). Weather patterns described here are averages, not a forecast for your dates.