Sea, Sand and Surf in Thailand: Andaman or Gulf, and When to Go

Updated 10th Sep 2026

Thailand has two coasts and they do not share a season. The Andaman side, west of the peninsula, takes the southwest monsoon from mid-May to mid-October. The Gulf side keeps raining after that, and its east-facing shores get more rain in that period than the Andaman side does.

Below are five stretches of coast, each with a different gateway airport, the marine park closures published for each, and the flights that reach them. None of the five is a Phuket beach, because the beaches of Phuket have their own page.

Andaman or Gulf: the two coasts run on opposite seasons

The Thai Meteorological Department (TMD) describes two monsoons on its own page about the monsoon winds, which is written in Thai. The southwest monsoon covers Thailand from mid-May to mid-October, bringing cloud and general rain, heaviest along the coasts and on the windward side of mountain ranges. The northeast monsoon runs from about mid-October to mid-February and brings cold, dry air down from the north, giving clear skies and cool, dry weather most noticeably in the north and northeast.

The south is the exception, and it is the exception that decides the booking. TMD states that during the northeast monsoon the south still has abundant rain, and that the south's east coast gets more of it than the south's west coast. Its account of the Thai seasons puts southern rain running through to December, often heavy enough to cause flooding.

So the Andaman coast is at its wettest and roughest from about mid-May to mid-October, and the Gulf coast takes its rain from about mid-October into December. TMD adds that the onset and the end of both monsoons can vary from the normal in any given year, and it declared Thailand's 2026 rainy season open on 15 May 2026. The UK Foreign, Commonwealth and Development Office (FCDO) puts the same split more bluntly for its own travellers, saying the rainy season is generally May to October but that in Koh Samui and the south-east of Thailand it is usually from November to March.

A trip can use both coasts. Phuket to Koh Samui and Krabi to Koh Samui are the flights that cross between them. For the national picture across the whole country rather than the coasts, see the best time to visit Thailand.

How these five stretches of coast were chosen

Four things decided the list:

• which sea the coast faces, and therefore which monsoon it takes;
• which months that monsoon covers, taken from TMD rather than from a general impression;
• the nearest airport with scheduled domestic flights, because a coast you cannot fly to is not an answer on this site;
• whether the coast sits in a national marine park with a published closure.

One stretch per gateway airport, so each entry is a different flight and a different part of the country. Three of the five face the Andaman Sea and two face the Gulf.

The closure dates below are the ones published in the National Park Office's closure list, which gives its own information as current at 7 January 2026. The file is hosted on Google Sheets rather than on a government domain, and it is the Tourism Authority of Thailand (TAT) that identifies it as that office's list. The list's own instruction is that each national park sets its own measures and conditions, so check with the park before planning around a date, and where a park publishes dates on its own page as well, both are given below.

Khao Lak and the Phang Nga coast, on the Andaman side

Khao Lak is a mainland coast in Phang Nga, running from Ban Nam Khem to Khao Lak - Lam Ru National Park. TAT describes it as suited to swimming and paddling, with watersports including skim boarding and stand-up paddleboarding. Piers on the Phang Nga coast are where boats leave for the Similan and Surin islands.

Mu Ko Similan National Park closes to visitors from 16 May to 14 October every year, its open season runs from 15 October to 15 May, and the closure covers the whole park including its accommodation. The park's own page gives both dates, and the National Park Office's list gives the same closure window while separately closing several of the park's named dive sites, Ko Tachai among them, with no end date. The park gives its reason plainly: the southwest monsoon may bring heavy rain and strong waves, and travelling there in that period is not safe for visitors.

Mu Ko Surin is the other full closure on this coast. The National Park Office's list gives it the same window, 16 May to 14 October. The park's own page says its passenger boat service runs until 16 May each year and then closes for the rainy season, without naming a reopening date.

Mu Ko Surin's own page gives the crossing from Kuraburi Pier as about 60 km, and one to two and a half hours depending on the boat. Mu Ko Similan's page records an average annual rainfall of 3,560 mm and an average temperature through the year of 27 degrees Celsius.

Phuket International Airport (HKT) is the gateway for this coast, and Airports of Thailand lists it among its own six airports. Bangkok to Phuket is the route that serves it.

Ao Nang and Railay in Krabi, on the Andaman side

Ao Nang, Noppharat Thara Beach and Railay all sit inside Hat Noppharat Thara - Mu Ko Phi Phi National Park. So do Ko Phi Phi Don, Ko Phi Phi Le, Ao Maya, Ko Yung, Ko Poda, Thale Waek and the shell cemetery. So the mainland beaches and the offshore islands sit inside one protected area.

The National Park Office's list shows no seasonal closure for the park as a whole and closes specific places instead. Ao Maya, Ao Lo Sa Ma and Ao Loko are closed from 1 August to 30 September every year. Ko Yung is listed as closed indefinitely, and diving on the west side of Ko Kai is listed as temporarily closed from 16 May onwards.

Ao Maya's closure falls in August and September, which is inside the Andaman wet season rather than at the end of it. It is a closure a monsoon rule of thumb does not predict. Koh Phi Phi covers the islands themselves.

Krabi Airport (KBV) is the gateway, and it is a Department of Airports airport rather than one of the six on the Airports of Thailand list. The department's own 2026 air-transport data records scheduled domestic flights there. Bangkok to Krabi is the route, and Ao Nang has a guide of its own.

The Trang coast: Hat Chao Mai and its islands, on the Andaman side

Hat Chao Mai National Park covers a stretch of the Trang coast. Its named sites include Ko Kradan, Ko Chueak, Ko Muk, Ko Waen, Morakot Cave, Changlang Beach, Pak Meng Beach, Yao Beach, San Beach and Yong Ling Beach. The park's welfare shop sells food and drinks and is open daily from 08.30 to 16.30.

The park's own page describes a climate that rains through the year, with summer from January to April, a rainy season from May to December, and annual rainfall over 2,100 mm. That runs later than the national picture, where TMD puts the Thai rainy season at about mid-May to mid-October. Both are worth knowing before booking November here.

The National Park Office's list closes Ko Chueak and Ko Waen from 1 June to 30 September, and Ko Muk and Ko Kradan from 1 August to 30 September. The same list closes Morakot Cave itself for the whole of September. Snorkelling and water activities on the reef in front of Ko Kradan are listed as temporarily closed from 15 May onwards.

Trang Airport (TST) is the gateway, and the Department of Airports' own 2026 air-transport data records scheduled domestic flights there. Bangkok to Trang is the route.

Koh Samui and Mu Ko Ang Thong, on the Gulf side

This is where the Andaman assumption fails. Mu Ko Ang Thong National Park, the archipelago reached from Koh Samui, is closed in the National Park Office's list from 1 November to 15 December: its tourist sites and its accommodation together. That falls in the middle of a period that a May-to-October rule of thumb marks as the dry half of the year.

The park's own English page supports the direction without giving those dates. It describes an archipelago hit by monsoon rain and severe storm surges, with average rainfall of 2,000 mm a year, and it names February to August as the time when the weather is hot, the sea is calm and sailing is at its best. The same 1 November to 15 December window appears in the list for Mu Ko Chumphon, so it is not one park's quirk.

If a day trip out to Mu Ko Ang Thong is the reason for the trip, the date is the first thing to check.

Koh Samui Airport (USM) is the gateway, and Bangkok Airways sells Bangkok to Koh Samui from Bangkok's Suvarnabhumi Airport (BKK) on its own site. Koh Samui has a guide of its own.

Koh Chang and the Trat coast, on the eastern Gulf

Mu Ko Chang National Park covers more than 40 islands, of which Ko Chang is the largest, over about 650 sq km of which roughly 458 sq km is water. On Ko Chang itself the sandy and rocky beaches are on the western side, and the east coast is mudflats and a narrow rocky beach.

The rain is the honest annoyance here. The park's own page gives an average annual rainfall of about 4,700 mm, against 3,560 mm at Mu Ko Similan and 2,000 mm at Mu Ko Ang Thong, all three published by the Department of National Parks, Wildlife and Plant Conservation. The same page puts the rainy season from May to October, winter from November to February and summer from March to April.

The closures the National Park Office's list publishes here are island-level and activity-level rather than a season for the whole park. Ko Thong Lang, Ko Kra and Ko Thian are listed as closed indefinitely, which is a harder thing to plan around than a season. A dive site at the coral restoration area off Ko Yak Yai is listed as temporarily closed to scuba from 11 November, and a hiking trail is closed from 1 June to 31 October.

Trat Airport (TDX) is the gateway, and Bangkok Airways sells Bangkok to Trat from Suvarnabhumi on its own site. Trat has a guide of its own.

Surfing in Thailand: one coast, one season, and it is marginal

Thailand has surf, and it is small: TAT's 2018 article on Thai surf spots describes flat, lake-like conditions outside a short swell season and, inside it, mushy onshore conditions that are inconsistent, windblown and rainy. The swell TAT describes arrives with the southwest monsoon, which TMD puts at about mid-May to mid-October.

That is the same window in which Mu Ko Similan and Mu Ko Surin are closed and the sea is at its roughest. The same article named breaks on Phuket's west coast and, on the mainland, Pakarang Cape at Khao Lak, which it called one of the few mainland spots in Thailand with good surf after New Year, often well into January and February.

January and February are the opposite half of the year from the monsoon window, and TAT does not reconcile the two. Its own Khao Lak page describes the coast as widely known as Thailand's "Surf Town".

If surfing is the reason for the trip, Thailand is a marginal choice. The monsoon swell season is short, the conditions inside it are onshore and inconsistent by the tourism authority's own account, and it falls in the same months as the Similan and Surin closures and the riptide warnings below.

Beach safety: the flags, and what to do in a rip

The Department of Disaster Prevention and Mitigation (DDPM) gives advice for swimming in the sea during the monsoon season, carried by the Government Public Relations Department.

If a current carries you away from the shore, wave for help and float with the current until help arrives. Do not swim against the current, because it will exhaust you. DDPM's emergency line is 1784, and it runs 24 hours.

The flag scheme in that advice has four states:

• Two red flags: the beach is closed, all activity is suspended, and it is extremely dangerous. No swimming at all.
• One red flag: danger. No swimming.
• Yellow flag: swim with caution.
• Red and yellow flag: a lifeguard patrols this stretch and swimming is permitted.

On national-park beaches, the Department of National Parks, Wildlife and Plant Conservation describes a shorter version of the same idea: yellow means the shore waves are moderate and swimming is still allowed, and red means the wind and waves are strong enough to put a swimmer in danger.

The rest of DDPM's advice is practical:

• check the forecast before travelling, and if a storm or high-wave warning is out, do not swim or do any water activity at all;
• stay away from deep water, high waves, strong wind, dangerous marine life, and any reverse current or undertow;
• do not do water activities during or after heavy rain;
• wear a properly fitting life jacket or an approved flotation device in the water;
• swim in designated areas, or where a lifeguard is on duty.

The FCDO gives British travellers the same warning in its own words, telling them to take care swimming off coastal areas, especially during the monsoon, because people have drowned in strong riptides. It also warns that jellyfish can swim close to shore particularly in the rainy season from May to October, and that jellyfish stings can be fatal.

Frequently asked questions

Which Thai coast is drier in November, the Andaman or the Gulf?

The Andaman coast is the drier of the two. During the northeast monsoon, from about mid-October to mid-February, the south as a whole still gets abundant rain, and the south's east coast gets more of it than the south's west coast. Rain on the southern Gulf side often continues through to December.

When does Mu Ko Similan National Park close?

From 16 May to 14 October every year, with the open season running from 15 October to 15 May. The park's own page gives both dates and the National Park Office's closure list gives the same closure window. The closure covers the whole park, accommodation included, and the list closes several of the park's named dive sites, Ko Tachai among them, with no end date.

Can I visit Mu Ko Ang Thong National Park from Koh Samui in November?

Not from 1 November, going by the National Park Office's list, which closes the park's tourist sites and accommodation from 1 November to 15 December each year. That is the reverse of the Andaman pattern, and the same window applies to Mu Ko Chumphon. Check with the park before booking a day trip in that period.

What do the beach flags mean on a Thai beach?

Two red flags means the beach is closed and all activity is suspended. One red flag means danger and no swimming, a yellow flag means swim with caution, and a red and yellow flag means a lifeguard patrols that stretch and swimming is permitted. The Department of National Parks, Wildlife and Plant Conservation describes only yellow and red on national-park beaches.

Is there a fee to enter a Thai national marine park?

The parks that publish the information charge on arrival and tell visitors to keep the receipt. Mu Ko Ang Thong National Park's own page says to carry the receipt for inspection after the entrance fee is paid.

Which airport serves the Trang coast and Hat Chao Mai?

Trang Airport (TST). The Department of Airports' own 2026 air-transport data records scheduled domestic flights there, and Bangkok to Trang is the route from the capital. This site carries an airport page and the Trang routes, but no separate destination guide for the province.