Best time to visit Thailand: north, Andaman and Gulf by season

Choose the coast before you choose the month

The useful distinction is Andaman versus Gulf, rather than “Thailand in summer” or “Thailand in winter”. Phuket, Krabi and the islands to their west face the Andaman Sea. Samui, Phangan and Tao sit in the Gulf. A good month on one side need not be a good month on the other.

When we checked on 2026-10-07, TAT’s monsoon guidance described May to October as the southwest monsoon period, with September taking the strongest rain. The same article placed the Samui-area rains in October to December, peaking in November and easing in January. That article was published in 2018: use it as a broad seasonal pattern, then consult the current forecast and the operator before a boat trip.

If the beach matters more than the rest of the route, choose it first. A plan that tries to rescue every rainy day with another island transfer tends to spend the holiday on piers. Stay somewhere with places to eat and things to do on land, and keep the boat day movable.

The north: a cool-season trip needs layers

TAT’s January 2026 column describes Chiang Mai’s cooler weather from November to February, and contrasts the city with much colder mountain mornings. Chiang Mai and Chiang Rai make comfortable bases for a mix of old-town walking, food and a day out in the hills. A mountain sunrise is a different outing from a city afternoon: pack a warm layer even when the forecast for the hotel looks tropical.

The same column highlights January’s wild Himalayan cherry blossoms around Ban Khun Chang Khian. They are a seasonal possibility, not a flowering appointment. Do not build a whole northern route around a photograph taken in another year; ask locally about the current blooms and whether the road is suitable for your transport.

For a short trip, stay in Chiang Mai rather than adding a new bed every night. A full day out can be followed by a quiet morning in town. If you add Chiang Rai, give it its own nights instead of treating the entire north as a string of roadside stops.

The Andaman: plan around the sea, not just the rain

TAT’s guidance warns that Andaman monsoon weather can affect ferries and other marine activities. Even with a ticket in hand, a crossing depends on the conditions at the time. A dry-looking morning at your hotel is not a sailing guarantee, and a cancellation is a reason to change the plan rather than shop around for a boat willing to go.

For an Andaman trip, Phuket or Ao Nang gives you a base accessible by road, from which to decide about the next day’s outing. A room on a smaller island can be lovely, but it adds a ferry to both ends of the stay. Keep that trade-off in mind when the international flight is close.

Seasonal park closures are another decision altogether. TAT’s January 2026 notice explains that national parks can close fully or partly for weather, safety and ecological recovery, with dates varying by attraction. Check the Department of National Parks and the individual park. We have not treated an old Similan or Maya Bay closure calendar as the current one.

The Gulf: a useful alternative, with its own wet months

Samui, Phangan and Tao are the islands named in TAT’s later-rain guidance. They can be worth considering when your dates fall in the Andaman monsoon period, but changing coasts does not remove the need to check the sea. Choose the island for the kind of stay you want, then check the actual connection from your arrival airport.

A week does not need all three islands. One base and a weather-dependent day trip usually leaves more time for the beach than a daily change of ferry and hotel. Samui is a practical starting point for comparing onward options; if Tao is the main reason for the trip, allow it real nights and a mainland buffer rather than fitting it between flights.

In October to December, keep the Gulf part of the route flexible. The broad TAT pattern peaks in November and tails off in January, but the day-to-day forecast is more useful than any month label once you are there.

How to match the route to your dates

These are editorial route choices, not official weather promises or timetables. Keep one coast rather than trying to sample both in a short holiday.

• November to February: start by comparing Bangkok, Chiang Mai and an Andaman base; add warm layers for the northern hills and check Gulf rain if Samui is your priority.
• May to October: consider a Bangkok-and-north trip with flexible outdoor days, or compare the Gulf islands with the wetter Andaman coast. Do not assume a marine park or ferry is operating.
• October to December: give special attention to the Samui-area forecast and sea conditions. Bangkok and a mainland base make it easier to change an outing without changing every hotel.
• A fixed departure flight: spend the previous night where you can reach the airport without a sea crossing. A spare night is more useful than one last island on the map.

Check parks, weather and transport again before you leave

Use the forecast for your destination, not just Bangkok. TAT directs travellers to the Thai Meteorological Department for storm, flood, high-wave and coastal warnings. Its September 2026 visitor update also shows how quickly railway, airport and marine plans can change after heavy rain. That update described the situation on 29 September, not a permanent assurance that every route is open.

Ask the tour operator what happens if the weather cancels the outing: refund, rescheduling, a different route or a land activity. Confirm whether a park fee is included and whether the park is open. For mountain days, ask about the walking involved and road access. Book the experience that fits the season rather than the season around a non-refundable experience.