Best Thai Islands by Month: Andaman or Gulf?
Go to the Andaman side from November to March and the Gulf side from April to September. Two dates shape the calendar: the Similan and Surin Islands close on 16 May and reopen after 14 October. The southwest monsoon runs from mid-May to mid-October.
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The short answer: Andaman in winter, Gulf in summer
If you can pick your month, go to the Andaman coast from November to March and to the Gulf coast from April to September, because each side is drier in those months. The Andaman Sea is the west side of the south, and the Gulf of Thailand is the east side.
The calendar turns on two dates. The Similan and Surin Islands close on 16 May and stay shut until after 14 October.
What the monsoons do
From mid-May to mid-October the southwest monsoon brings heavy rain, most of all along the coasts. From about mid-October the northeast monsoon takes over and runs to mid-February.
The south stays rainy under this second monsoon, and the east side more than the west. Heavy rain there continues until December.
| Months | What to expect | Better coast |
|---|---|---|
| November to March | Gulf rain peaks in November; Andaman is drier | Andaman |
| April to September | Andaman rain climbs; Gulf stays lighter | Gulf |
| October | Wet on both coasts | Neither |
October is the one month I would skip for both coasts. Treat the table as a guide to the coast, not to your exact beach.
Marine park closures
Check the closures before you fix a sailing date. Each park closes some sites for part of the year.
| Park or site | Closed |
|---|---|
| Similan Islands | 16 May to 14 October |
| Surin Islands | 16 May to 14 October |
| Maya Bay, Loh Samah, Lo Ko bay (Phi Phi) | 1 August to 30 September |
| Phang Nga Bay: Koh Lawa Yai, Ao Khian, Koh Boi Yai | 1 August to 30 September |
| Koh Rok (Lanta park) | 1 June to 30 September |
| Koh Ha, Hin Muang-Daeng (Lanta park) | 1 August to 30 September |
| Tarutao: Adang, Rawi and listed islands | 1 June to 30 September |
| Hat Chao Mai: Koh Cheuk, Koh Waen | 1 June to 30 September |
| Ang Thong Islands (Gulf) | 1 November to 15 December |
| Koh Samet: Koh Kudi | 1 July to 15 August |
| Koh Samet: Koh Talu | 16 August to 30 September |
Similan opened for the 2026 season on 15 October, so late October works for both Similan and Surin. If Maya Bay is your goal, avoid August and September. On the Gulf side, Ang Thong shuts some sites before mid-December.
Which month fits you
From late October to December, the Andaman parks reopen and the rain there is lighter than on the Gulf side.
From January to mid-February, nothing on the Andaman list is closed, so this is an easy time to go.
Mid-February to mid-May is the hot season, and Similan and Surin close on 16 May.
From mid-May to mid-October, the Andaman parks start closing and the coast gets the monsoon rain. Koh Rok, Tarutao and Hat Chao Mai close from 1 June, then Maya Bay and Phang Nga Bay’s listed sites from 1 August.
Treat all of these dates as the usual pattern, because the monsoons can start and end away from them in any year. Some sites can also change their opening with the weather.
For the whole country, see the best time to visit Thailand guide. Island pages: Koh Lanta, Koh Lipe, the Similan Islands and Koh Chang.
Photos (2)
- Max Maier
- Alejandro Dugar
Not confirmed: The rainy season can start 1 to 2 weeks early or late; check the park announcement for your sailing date.
Common questions
Which Thai island coast is best in December?
The Andaman side. Heavy rain in the south lasts until December, and the east side gets more of it.
When is the rainy season in Thailand?
It runs from mid-May to mid-October. In the south the rain carries on until December.
When do the Similan Islands close?
The park closes from 16 May to 14 October.
When is Maya Bay closed?
From 1 August to 30 September.
Are the Surin Islands open in July?
No. Surin is closed from 16 May to 14 October.
Do monsoon dates change each year?
Yes. Both monsoons can start and end away from their normal dates.
Read next
Sources and reader comments
Official legal texts (Gazette, government portals):
- Thai Meteorological Department: Climatological Data of Thailand for 30-year period 1991-2020 (Meteorological Data report 551.586-13-2023) (opens in a new tab)
- Royal Gazette 9 Jan 2026: DNP announcement closing tourism and overnight stays in national parks and forest parks, B.E. 2569 (annex dated 18 Dec 2025) (opens in a new tab)
- Thai Meteorological Department: climate of Thailand (Thai page: monsoons, seasons, regions) (opens in a new tab)
- DNP news, 16 Oct 2026: Similan Islands open for the season on 15 October 2026 (opens in a new tab)
- DNP news, 15 Oct 2026: Andaman marine parks open for the season (opens in a new tab)
Prices, timetables and opening hours change; check with the operator before you travel. See how guides are checked.
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Comments (5)
AstroTommy
I recommend Koh Samet, it's a popular islands weekend holiday spot for locals from Bangkok. The island has a national park on it, it's a few hours by bus from Bangkok Ekamai station
peteyy_cz
just don’t go to Phuket, fly to Krabi that’s like a 2 hour flight from over there. I’d recommend Ao Nang beach find a cheap hotel and hang around the beach for a few days. You can go to Phi Phi by boat from there for a day trip.
tallwhiteguycebu
I second this, just fly to Krabi and stay in Ao Nang. They have these long tail boats that will take you to different beaches for 200 baht round trip
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thehotflashpacker
I just spent 16 days at Koh Lanta. (Khong Dao beach). Had a nice pool, super easy swimming beach. Not so expensive excursions by motor boat to good snorkel spot, phi phi, and emerald cave. Small night market, lots of chill bars and restaurants to chose from. Easy ride from Krabi airports (2 hrs).
cliff0217
Less about the type of beach, more about weather. Also, you didn't state the length of time. You need to go in with expectation that it will rain, and to be flexible when it does. I think Aug/Sept, Samui has least amount of rain. I suggest renting a car. To me, Samui is compact, has good hiking spots, easy to find food, and more options for mid-level/high-end hotels - ultimately it attracts a more mature traveler. You'll run into partygoers because it's a docking point for Phangan, but for the most part, prices out many tourists. Some would say Hua Hin, but to me, it's a weekend trip (if that's what you want, then great). Hope this helps!