Similan Islands: Last Weeks to Dive Before the 2026 Season Closes

The Clock Is Ticking on the Similan Season

Every year, the Similan Islands National Park shuts its doors around mid-May and doesn't reopen until mid-October. For the 2025-2026 season, most liveaboard operators are running their final trips between late April and the first week of May. After that, the monsoon takes over and the Andaman Sea becomes a no-go zone for dive boats.

If you've been putting off a Similan trip, you've got roughly four to five weeks left. And here's the thing most people don't realize — these final weeks often deliver the best conditions of the entire season.

Why April and Early May Are the Sweet Spot

March gets all the hype, but April quietly delivers cleaner water and fewer boats. Visibility regularly hits 25-30 meters at sites like Koh Bon and Richelieu Rock. The thermoclines that made February dives unpredictable have mostly settled, and surface conditions stay calm through most of April.

Water temperatures hover around 28-30°C, so a 3mm wetsuit or even a rash guard works fine for most people. The currents at Koh Tachai and the northern sites pick up slightly, which is actually good news — stronger flow brings more plankton, and more plankton brings the big stuff.

Manta rays patrol Koh Bon's ridge consistently through April. Whale sharks cruise past Richelieu Rock and Koh Tachai with surprising regularity in the final weeks. These aren't rare sightings — operators report encounters on roughly 60-70% of late-season trips to these sites.

The Dive Sites You Can't Miss

A typical Similan liveaboard covers four major areas, and each one has a different personality.

• Similan Islands (Islands 1-9): The granite boulders here create swim-throughs, caverns, and dramatic walls. Christmas Point on Island 9 is the standout — huge boulders stacked at impossible angles with soft corals and sea fans everywhere. East of Eden on Island 7 offers a gentler slope with turtles, moray eels, and reef sharks.
• Koh Bon: A submerged pinnacle on the west side drops from 18 to 40+ meters. This is manta territory. The cleaning station at 22 meters pulls mantas in almost daily during April. Leopard sharks rest on the sandy bottom, and barracuda schools circle the pinnacle.
• Koh Tachai: Strong currents make this an advanced site, but the reward is pelagic action — trevally, tuna, and the occasional whale shark. The pinnacle rises from 30 meters to about 12 meters below the surface, and the drift along it feels like flying.
• Richelieu Rock: Arguably the best dive site in Thailand. This horseshoe-shaped pinnacle is covered in purple and orange soft corals and absolutely packed with life. Seahorses, ghost pipefish, harlequin shrimp on the macro side. Whale sharks, barracuda walls, and giant groupers on the big side. You could do ten dives here and see something new every time.

What a Late-Season Liveaboard Trip Looks Like

Most Similan liveaboards run 4-day or 5-day itineraries departing from Thap Lamu pier near Khao Lak. A few longer 6-day routes extend south to the Surin Islands or north toward the Myanmar border. You'll typically log 15-18 dives over a 4-day trip, including night dives at sheltered Similan anchorages.

Daily routine: wake-up dive at 6:30 AM, breakfast, second dive mid-morning, lunch, afternoon dive, dinner, optional night dive. It sounds packed, but there's plenty of deck time between dives for napping, reading, or just watching the islands slide by.

Mid-range boats like the Sawasdee Fasai, Deep Andaman Queen, or MV Pawara offer en-suite cabins, three meals a day mixing Thai and Western food, and free tea and coffee. Beer and soft drinks are available for purchase onboard. Solo travelers are welcome — operators match you with a same-gender cabin mate or offer a single supplement.

Prices and Deals for the Final Trips

Late-season pricing works in your favor. Operators want to fill cabins before the shutdown, so discounts of 15-30% are common in April. Here's what the market looks like right now:

• The Junk: May 4 departure, Similan and Surin Islands route, from €789 (flash sale ends April 10)
• Sawasdee Fasai: All remaining 2026 trips from $772 (20% off regular price)
• Seatopia: May 26 departure, South Andaman route, from €566
• MV Raga: April 26 - May 1, 5 days/4 nights, Similans + Richelieu Rock, 42,500 THB
• Big Blue Diving: April 14 departure, cabins from 43,800-49,800 THB

Most operators include transfers from Phuket Airport or Khao Lak hotels, all meals, tanks, weights, and a dive guide. Gear rental runs around 500-800 THB per day extra. Nitrox is sometimes included, sometimes 200-300 THB per fill.

How to Get There

All Similan liveaboards depart from Thap Lamu pier, which sits about 30 minutes south of Khao Lak town. From Phuket Airport, it's a 90-minute drive north. Most operators offer shuttle transfers — expect to pay around 500 THB for a shared van from Phuket or get a free pickup from Khao Lak hotels.

If you're coming from Bangkok, the easiest option is to fly into Phuket (1.5 hours, flights from 1,500-3,000 THB one way) and take the transfer from there. Some divers fly into Surat Thani and drive across, but that adds 4+ hours and isn't worth the hassle unless you're already on the Gulf side.

Arrive the afternoon before your departure. Thap Lamu itself has a few guesthouses, or stay in Khao Lak for more restaurant and accommodation options. The boat typically departs between 6-8 PM, so there's no rush if your flight lands midday.

Booking Tips for a Last-Minute Trip

Spots fill fast in the final weeks. Here's how to lock one down:

• Book direct: Operator websites often have lower prices than aggregator sites, plus perks like free gear rental or nitrox.
• Check your certification level: Most boats require Open Water minimum, but Koh Tachai and Richelieu Rock dives go to 30+ meters. Advanced Open Water gives you access to all sites.
• Recent experience matters: Some operators ask when your last dive was. If it's been over 12 months, consider a refresher dive in Khao Lak or Phuket before boarding.
• Deposits are usually 30%: Final payment is due 60 days before departure, but for late bookings you may need to pay in full immediately.
• Flexible cancellation: Many operators still offer COVID-era rescheduling policies. Ask before booking.
• Bring your own gear if possible: Rental gear on boats is serviceable but not always the right fit. Your own mask and computer make a big difference.

Make It Happen Before Mid-May

The Similan Islands don't do rainchecks. Once the park closes, that's it until October. And while October-November openings can be good, they're hit-or-miss with leftover monsoon swells and reduced visibility.

April's combination of warm water, big animal encounters, discounted liveaboard prices, and fewer crowds makes it the smartest time to go — if you act quickly. Check current availability on siamdive.com and lock in your spot before the season slips away.