Season dates
When the Similan Islands Open and Close
Mu Ko Similan is shut by law for five months a year. The season runs 15 October to 15 May — here is why, and what it means for booking.
Check dates and availability ↗Mu Ko Similan National Park season calendar
| Period | Status | Set by | Notes |
|---|---|---|---|
| 15 October – 15 May | Open to visitors | DNP order | Park hours 08:00–16:00 daily |
| Mid-May – 14 October | Closed to all visitors | DNP order | Applies to Mu Ko Similan and Mu Ko Surin together |
| 15 May 2026 | Last day of 2025–26 season | DNP | Closure announced for 15 May – 15 October 2026 |
| 15 October 2026 | 2026–27 season opens | DNP | Exact date confirmed by DNP shortly before opening |
| Nov – Apr | Full operating window | — | All day-trip and liveaboard operators running |
Why the park shuts for five months
The Similan Islands are not a year-round destination, and that is a legal fact rather than an operator preference. Each year Thailand's Department of National Parks orders Mu Ko Similan closed for the southwest monsoon, alongside neighbouring Mu Ko Surin. Two reasons are given publicly. Crossing roughly 70 kilometres of open Andaman Sea in monsoon swell is genuinely dangerous for small passenger boats, and the reefs benefit from a season without anchor chains, fins and sunscreen. The department also uses the window to repair ranger stations and mooring buoys. No operator can legally run a trip during the closed months.
The exact dates, and how firm they are
The published season runs 15 October to 15 May. For 2026 the department announced the closure as 15 May to 15 October, with the islands reopening for the 2026–27 season in mid-October. In practice the mid-October opening has been stable for years, but the department confirms it formally only shortly before the season starts, and retains discretion to shift for weather or conservation reasons. Treat 15 October as the working assumption and expect confirmation in the first half of October. The closing date is applied more predictably, since it is fixed to the monsoon calendar.
What this means for planning
The closure compresses all Similan tourism into seven months. Boats and liveaboard cabins over Christmas, New Year and Chinese New Year sell out weeks ahead, because supply is capped by the daily visitor limit and cannot expand to meet demand. Shoulder periods in late October and early May are quieter and cheaper, but early-season seas can still be lumpy as the monsoon retreats. If your Thailand dates fall between mid-May and mid-October, no amount of searching will find a legitimate Similan trip. Operators marketing Similan tours in those months are usually selling a different destination.
Where operators go in the closed season
Andaman operators do not simply stop. Between mid-May and mid-October, Khao Lak and Phuket boats redirect to sites that stay open through the monsoon, including day trips around Phuket's own coastline and the Phi Phi group, and dive sites in sheltered waters east and south of Phuket. Some Khao Lak dive centres close entirely and reopen in October. This matters if you are booking accommodation in Khao Lak, which is heavily seasonal: a town built around Similan departures becomes very quiet once the park shuts.
Booking around the reopening date
Because the reopening date is confirmed late, tours for the first days of a season are sometimes listed as provisional. Sensible practice is to avoid scheduling your only possible Similan day on 15 or 16 October. Give yourself a few days of slack in mid-to-late October, or book from the start of November when the season is unambiguously running and sea conditions have usually settled. Booking platforms with free cancellation up to 24 hours before departure remove most of the risk either way.