Ang Thong is the one Koh Samui day trip with a fixed shut season: the national park closes completely from 1 November to 15 December every year. Outside that window, mid-February to April is the driest and calmest stretch. Below you will find what each month brings, which boat suits your dates, how busy the islands actually get, and a date check that tells you whether the park is open on yours.
Ang Thong is not open all year, and the annual closure is the first thing to check your dates against: the park is closed completely from 1 November to 15 December, whatever the forecast says. It reopens into December, the busiest month of the year on Koh Samui. Outside that window, what decides whether a booked day actually happens is the sea rather than the rain — this is a 30 km open-water crossing each way, and the park shut for a full day on 8 January 2026 on a two-to-three-metre wave warning.
If your dates are flexible, aim for mid-February to April. Those are the driest weeks of the year, the northeast monsoon has left the Gulf, and it is the window the park authority names itself for calm sea and clear water, which is what a full day built around kayaking, snorkelling and a 500-metre viewpoint climb depends on. April is the busiest of the three.
If your dates are already fixed for the summer, the trip holds up better than the season's reputation suggests. June and September are the quietest months of the year — June has the fewest visitors, September the emptiest hotels — and both take less rain than May. The trade-off is the southwest monsoon: afternoon showers, and 15 or 16 days a month with some rain on them against February's six. Whatever your dates, the choice still open to you is the boat: a big boat rides out a swell that a speedboat slams into.
Check dates and prices — from $68 Is the park open on my date?
Once your dates clear the closure, the month decides two things: how much rain lands on the crossing, and how many other boats are at the same anchorage.
Mid-February to April is the best window overall. February takes 58 mm of rain across the whole month against 490 mm in November, March records the fewest days with rain of any month at five, and the sea between the two monsoons is at its steadiest, which is what a 30 km crossing and a snorkelling stop both rest on. The drawback is April: hotel occupancy reaches 81%, the highest of the three, and the stops are correspondingly fuller.
December and April are the two peaks for beds on Koh Samui, and December carries the extra problem that the park is shut for its first fifteen days. October and November are the wettest months of the year by a wide margin, at 290 mm and 490 mm.
June and September are the quietest. June has the fewest visitors of any month and September the emptiest hotels at 72% occupancy, and both take less rain than May. The trade-off is the southwest monsoon: expect afternoon showers, more days with some rain than February gets, and a higher chance that a rough morning moves your departure.
Below, the months are compared in detail, with rainfall, days with rain, hotel occupancy and the park's status for each.
Put in the day you are thinking of. The card tells you whether the park is open, what the conditions usually look like, and which boat suits them.
Pick a date above
Without a date, the year in one line: the park is shut 1 November to 15 December, February and March are the driest months, and October and November are the two wettest.
February averages about 58 mm of rain across the whole month and six days with any rain. November averages about 490 mm and twenty. Every other month sits between the two.
Inside the forecast window the card reads a live forecast for the islands and says so. Beyond it, the card shows the long-run average for that month and says that instead.
Koh Samui and Ang Thong sit on the Gulf side of the peninsula, which runs on the opposite monsoon clock to Phuket and the Andaman coast.
Two winds decide the year here. The southwest monsoon runs from about mid-May to mid-October and soaks the Andaman coast, but the Gulf side is in its lee, so on Samui it shows up as afternoon showers instead of washouts. The northeast monsoon arrives from about mid-October and does the opposite: it pushes moisture straight onto this coast, which is why the east side of southern Thailand is still in heavy rain in November and December when Bangkok has already dried out. Everything below follows from those two dates.
Mid-February to April is the gap between them. The northeast monsoon has gone, the southwest has not arrived, and the crossing to the islands is at its steadiest. This is when the limestone stacks stand out of flat water, the snorkelling stops are clear rather than stirred up, and the 500-metre climb on Koh Wua Ta Lap is a view instead of a cloud. The park authority points at the same window in its own visitor guidance.
May to September is the southwest monsoon. It is the part of the year most travellers write off before checking. The islands stay green, the sea is workable most days, and the showers tend to be short. September is the quietest month on Koh Samui and takes less total rain than May.
October to mid-December is the northeast monsoon proper. October rain climbs to roughly five times a February month, November is the wettest month of the year, and the park is closed from the first of November. When it reopens in mid-December the sea is still unsettled, and December is simultaneously the busiest month of the year for beds on the island.
| Month | Rain | Days with rain | Hotels full | Ang Thong |
|---|---|---|---|---|
| January | 138 mm | 11 | 77% | Open. Monsoon tail, rough days happen |
| February | 58 mm | 6 | 77% | Open. Driest month of the year |
| March | 78 mm | 5 | 78% | Open. Fewest days with rain |
| April | 77 mm | 8 | 81% | Open. Dry, hot, and the busiest dry month |
| May | 147 mm | 15 | 77% | Open. Showers start, sea builds |
| June | 113 mm | 15 | 75% | Open. Fewest visitors of the year |
| July | 123 mm | 14 | 74% | Open. Sheltered from the Andaman monsoon |
| August | 119 mm | 15 | 74% | Open. Similar to July |
| September | 117 mm | 16 | 72% | Open. Emptiest hotels of the year |
| October | 290 mm | 20 | 73% | Open, but the rain ramps up hard |
| November | 490 mm | 20 | 74% | Closed all month. Wettest month |
| December | 209 mm | 14 | 82% | Closed to 15 Dec, then open. Busiest month |
Between the monsoons Southwest monsoon Northeast monsoon Wettest stretch Park closed
Rain is the average total for the whole month and days with rain is the average count of days recording any. Hotels full is the share of rooms occupied across Surat Thani province, averaged over the last three complete years. Daytime highs sit between 29 and 33°C in every month of the year, and daylight varies by barely an hour between the solstices, so neither is a reason to pick one month over another.
The month does not change what you see at Ang Thong. It changes how the crossing feels, and that is a boat decision.
A speedboat gets you there in about 45 minutes and gives you longer on the islands. It also slams in a swell. A big boat takes roughly twice as long and rides the same swell far more comfortably. In February and March that difference barely matters. From May onward it is the main thing to get right, which is why the cheapest option on this page is often the better one for a summer date.
Best for May to October dates
From $38 · 4.35 stars · 5,089 reviews · 9 hours
The steadiest ride in the fleet and the cheapest trip that still includes kayaking and the Talay Nai lagoon. Slower on the water, which is exactly what you want when the southwest monsoon is putting a swell into the Gulf.
Best for February to April dates
From $68 · 4.69 stars · 2,026 reviews · 8.5 hours
The highest-rated of the standard full-day trips, and the one this page recommends for the dry window. Speed buys you time on the islands, so the viewpoint climb, the lagoon and the snorkelling all fit without a rush.
Best for December and April, when beds are fullest
From $128 · 4.84 stars · 1,905 reviews · 10 hours
The highest rating on this page by some way. In the two months when occupancy on Samui is above 80 per cent, the stops themselves get crowded, and a smaller boat is the only part of that you can actually control.
Best if you are staying on Koh Phangan
From $78 · 4.53 stars · 1,046 reviews · 9 hours
The same park, the same stops, leaving from the other island so you skip the ferry. It costs more than the Samui equivalent because the run is longer.
Prices are the lowest advertised per person and were checked on 8 September 2026; ratings and review counts were re-checked against the live listings on 9 September 2026. They move with season and demand, so the booking page is the figure that counts. For the longer argument between the two hull types, see our speedboat versus big boat comparison.
If your dates land inside the Ang Thong Marine Park closure, the boats that still run go elsewhere. Koh Tao and the Koh Nang Yuan sandbar hold some of the clearest snorkelling water in the Gulf, and a Koh Madsum (Pig Island) and Koh Tan trip from Koh Samui stays in sheltered water close to shore. Live options below.
The single hard fact on this page, and the one worth checking your dates against first.
Mu Ko Ang Thong shuts to visitors from 1 November to 15 December every year, by annual order of Thailand's Department of National Parks. It is a park-wide closure for monsoon safety and for letting the beaches and reefs recover, not a run of weather cancellations, so it applies to every operator regardless of what the forecast says on the day.
Outside the closure the national park entrance fee is 300 baht for adults and 150 baht for children, payable in cash on arrival unless your operator has already included it. Our park guide sets out what each ticket covers.
The Pig Island and Koh Tan snorkelling day is the closest substitute in sheltered water, from $42 with 5,483 reviews behind it. Availability is the thing to check, since the same weather that closes the park can stop other boats too.
A whole recommendation rests on the gap between 58 mm and 490 mm, so it is fair to ask what those numbers actually describe.
Every rainfall figure on this page is the total depth of rain across a whole month in an average year. It is not a daily rate and it is not a forecast for your day. A month with one violent storm and a month with three weeks of drizzle can total the same.
That is why the days-with-rain column sits next to it. Between them the two say something a single number cannot. September takes 117 mm across about sixteen days, so the rain is frequent and light. October takes 290 mm across twenty, so it is both frequent and heavy.
The honest version of the headline is narrow: an average November delivers more than eight times the rain of an average February. It does not mean rain is eight times more likely, or that there are eight times as many wet days. November records about twenty days with rain and February about six. Those are different measurements and the page has both.
For a day trip, days with rain is usually the more useful column. A 45-minute crossing and six hours on the islands do not care about a monthly total.
Crowding is measurable, and on Koh Samui the measurements are less dramatic than the seasonal language suggests.
Thailand's tourism ministry publishes hotel occupancy and visitor numbers for every province every month. Averaged across the last three complete years for Surat Thani, which covers Samui, Phangan and Koh Tao, the picture is this. December is the busiest month on both measures. April is second. September has the emptiest hotels of any month, and June draws the fewest visitors. February, despite being the best-weather month, sits below the annual average on both.
The more useful finding is how narrow the band is. Occupancy runs from 72 per cent in September to 82 per cent in December. Visitor numbers move by about thirty per cent between the quietest month and the busiest. Koh Samui does not empty out in low season, and it does not become unbearable in high season either, so holding out for a quiet month buys less than the phrase implies. What that does mean in practice: February gives you the driest weather without the December and April crush, which is an unusually clean combination.
One caution about the figures. They count paid accommodation and arrivals across an entire province, and Ang Thong is a day trip taken by a fraction of those people. They are a good guide to how much competition there is for a boat seat in a given week. They are not a headcount of anyone on the water.
Eight periods in date order, with what to expect and which boat to book.
Keep a backup day
138 mm 11 wet days 77% full
Drying out but still inside the northeast monsoon. Rough days happen and single-day park closures happen with them. Book a trip with free cancellation.
Recommended
58–78 mm 5–8 wet days 77–81% full
February is driest, March has the fewest wet days, April is dry and hot and the busiest of the three. Book the boat a few days out, once you can see a forecast.
Quietest for visitors
113–147 mm 15 wet days 75–77% full
The southwest monsoon arrives, mostly as afternoon showers. June draws the fewest visitors of any month, which shows up in how easy it is to get a seat.
Better than the Andaman coast
119–123 mm 14–15 wet days 74% full
A good time to be on this coast, while the Andaman side takes the monsoon head on. Both months stay under 125 mm and the sea is generally workable.
Emptiest hotels of the year
117 mm 16 wet days 72% full
Less total rain than May, June or July, and the lowest hotel occupancy of any month. The rain is frequent but light, and boats run normally.
The rain ramps up
290 mm 20 wet days 73% full
A different proposition to September: five times February's rain, with the northeast monsoon setting in and sailings pulled more often as the month goes on.
Park closed
490 mm in November 20 wet days Nothing runs
The park is shut by government order. Plan a Koh Tao or Pig Island day instead, and treat Ang Thong as a reason to come back.
Busiest month of the year
209 mm 14 wet days 82% full
The park reopens into the highest occupancy and visitor numbers of any month. Book early for Christmas and New Year week, accept that the sea can still stop a sailing, and check before you travel in case the reopening has slipped.
Whatever your window, the booking pattern is the same. Fix the accommodation early if you are travelling in December or April, and leave the boat itself until two or three days out, when a forecast exists and you can pick the hull that suits it.
Tap a question to open the answer.
No. Mu Ko Ang Thong closes to visitors from 1 November to 15 December every year, by annual order of the Department of National Parks. It is a park-wide closure for monsoon safety and habitat recovery, not a weather cancellation, so it applies to every operator whatever the forecast looks like. If your dates fall inside it, a Koh Tao or Pig Island boat day is the usual swap. Reopening is condition-dependent and can slip a few days past 15 December, so confirm with your operator if you are booking the third week of the month.
February, at about 58 mm of rain across the whole month and roughly six days with any rain at all. March is close behind on total rainfall, at about 78 mm, and actually records the fewest wet days of the year, around five. Those two months sit between the northeast monsoon leaving the Gulf and the southwest monsoon arriving, which is why they are also the calmest stretch for the crossing.
No. September takes about 117 mm of rain, less than May, June or July. It is also the quietest month of the year for hotel occupancy across Surat Thani province. It does record slightly more days with some rain than May, so showers are more frequent but lighter. The park is open and boats run normally.
Yes, individual days get cancelled when the sea is too rough to cross safely, and this is not limited to the wet season. The park itself shut for a full day on 8 January 2026 after the regional meteorological centre warned of waves of two to three metres in the Gulf. No public series of cancellation rates exists, so treat this as a risk to plan around, not a probability anyone can quote. Booking a tour with free cancellation and keeping a spare day in your itinerary is the practical response.
December, on both official measures. Averaged over 2023 to 2025, December records the highest hotel occupancy of any month in Surat Thani province and the highest visitor numbers, and the park is shut for its first fifteen days. April is next. The quietest months are September by occupancy and June by visitor numbers. The whole spread is narrower than most people expect, though: the busiest month draws about thirty per cent more visitors than the quietest, not several times more.
Every figure above, and where it stops being able to tell you anything.
Compare the full-day options for your travel window: duration, hull type, group size and cancellation policy in one place.