The Similan Islands close every year from 15 May to 14 October, and reopen for visitors on 15 October. That annual rhythm barely changes: Mu Ko Similan National Park shuts for the entire southwest-monsoon season and opens through the dry months, so the practical rule is simple — you can visit from mid-October to mid-May, and you cannot for the five months in between. In 2026 the park is closed now and reopens on 15 October 2026 for the 2026–27 season. Exact dates are confirmed each year by Thailand’s Department of National Parks, so double-check before booking travel built entirely around the reopening week.
The Similan season at a glance
| Period | Status | What it means |
|---|---|---|
| 15 October – 14 May | OPEN | Day trips and liveaboards run; calm seas, peak visibility Nov–Apr |
| 15 May – 14 October | CLOSED | Entire national park shut — no landings, no diving, no exceptions |
Why the park closes for five months
The closure is part weather, part deliberate conservation. The southwest monsoon (roughly May–October) brings the year’s roughest seas to the outer Andaman — the Similans sit a long way offshore in open water, and monsoon swell makes the crossing genuinely hazardous for day boats. At the same time, the five-month pause lets the ecosystem recover from high-season traffic: coral regenerates, fish stocks rebuild in untrafficked water, and turtles nest undisturbed. It is the same logic behind the annual Maya Bay closure, applied to a whole archipelago. When the park reopens, daily visitor numbers are capped (3,850 per day in recent seasons) to keep the recovery from being undone in a single high season.
Planning around the dates
If the Similans are the centrepiece of your trip, aim for November to April — the seas are at their calmest and underwater visibility at its best; the shoulder weeks right after the October reopening are quieter and the reefs are at their freshest. If your holiday falls inside the closure window, the wider region does not shut with the park: our guide to which Phuket islands stay open in the monsoon season covers the alternatives, and the broader best time to visit Phuket guide sets out the season trade-offs island-wide.
An honest note on Similan day trips from Phuket
Simba Sea Trips does not run Similan day tours from Phuket — and that is a deliberate safety decision, not a gap in the brochure. I have been on the water most of my life and running boats commercially in Phuket since 2014, and the maths of that route has never sat right with us: the Similans are a very long way offshore, and if a twin-engine speedboat loses one engine out there — which genuinely happens in marine operations — the return leg becomes a five-to-six-hour crawl, putting passengers back at the dock after dark in deteriorating conditions. Operators who accept that risk profile with a full boat are making a different call than we are willing to make.
Our honest advice if the Similans are a must: base yourself in Khao Lak, the closest mainland departure point, which shortens the exposed crossing dramatically. Go in with open eyes, though — most Khao Lak Similan boats are high-volume operations carrying 30-plus passengers, a very different day from a small-group trip. And if what draws you is clear water, dramatic rock and world-class snorkelling rather than the name itself, the Phi Phi Sunrise tour (฿5,310 per person, all-inclusive, maximum 18 adults) and our other join-in tours deliver that year-round, an hour’s ride from Phuket rather than an expedition.
More on the Similans
For what the islands are actually like — the diving, the granite boulders, how to get there from Khao Lak — see the full Similan Islands guide and the Similan Islands destination page.
