The Best Time to Visit Pig Island (Koh Madsum)
Month-by-month rainfall and sea conditions for Koh Madsum boat trips, when tours get cancelled, and whether to book the morning or the afternoon departure.
Koh Samui runs on a different calendar from the rest of Thailand, and Pig Island trips run on a different calendar again, because a boat trip cares about the sea rather than the sky. The short answer is late January through April, with February the driest month of the year. The longer answer is that plenty of months outside that window are perfectly good for Koh Madsum, and one month is genuinely worth avoiding.
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Koh Samui Misses the Monsoon That Closes Phuket
This is the fact that trips up most first-time visitors to Thailand. The southwest monsoon runs from roughly May to September and hammers the Andaman coast, which is why Phuket and Khao Lak go quiet in that stretch. Koh Samui sits on the other side of the peninsula, in the Gulf, and largely misses it.
So the months when the west coast is at its wettest are ordinary months here. Rainfall on Koh Samui between May and September runs between about 100 and 135 mm a month, which is a scattering of afternoon showers rather than a season. If your dates are fixed in July or August and you were worried, do not be.
The Gulf has its own wet season instead, arriving with the northeast monsoon in October and running through December. That is when Pig Island trips get cancelled.
The Numbers, Month by Month
Rainfall figures below are long-run monthly averages for Ko Samui. Sea temperature never drops below about 28°C in any month, so water temperature is never the deciding factor here.
| Month | Rainfall | What it means for a boat trip |
|---|---|---|
| January | 125 mm | Improving through the month; the back half is usually settled |
| February | 65 mm | The driest month, and the safest bet for calm water |
| March | 115 mm | Still firmly in the dry window, hot and clear |
| April | 85 mm | The last dry month, and the hottest |
| May | 130 mm | Showers arrive but the sea stays workable |
| June | 135 mm | Ordinary; trips run normally |
| July | 115 mm | Ordinary; trips run normally |
| August | 100 mm | One of the drier mid-year months |
| September | 120 mm | Fine, but the last comfortable month before the turn |
| October | 295 mm | The northeast monsoon arrives; cancellations begin |
| November | 445 mm | The wettest month of the year — expect disruption |
| December | 265 mm | Improving from mid-month; settled by the end |
November is the outlier, and by a distance. At roughly 445 mm it carries nearly seven times February’s rainfall, and the problem for a Pig Island trip is not the rain so much as what the northeast monsoon does to the sea. Rough water means shortened itineraries, dropped reef stops, and outright cancellations.
What Actually Gets Cancelled, and In What Order
Operators do not simply call off a whole trip when the weather turns. They strip it down in a predictable sequence, and knowing the order tells you what you are risking.
The kayaking goes first. Any listing that includes kayaks around Koh Madsum drops them in low tide, big waves or strong wind, while everything else runs.
The reef stop at Koh Tan goes second. Snorkelling depends on both sea state and visibility, and neither is guaranteed on any tour on this site. On a private charter a cancelled reef stop usually means extra time at Pig Island rather than a refund; on a shared boat the itinerary just gets shorter.
Longtail departures go third. An open wooden boat sitting low in the water is a poor place to be in a short sea, so longtails are pulled from the schedule on mornings when speedboats still run. If you are travelling in October or November and want the traditional boat, build in a spare day.
The whole trip goes last, and every tour here offers free cancellation up to 24 hours before departure. Several operators also offer a full refund or a reschedule for a weather cancellation on the day, which is worth confirming on the specific listing you book rather than assuming.
Morning or Afternoon Matters More Than the Month
Within any given day there are two schedules, and for most of the year the choice between them shapes the experience more than the calendar does.
Morning departures leave the south coast between roughly half past eight and half past nine. Wind in the Gulf tends to build through the day, so morning water is usually flatter. The pigs are also at their liveliest before the heat sets in — they come down to the water line when boats arrive and they do it with more enthusiasm at ten in the morning than at four in the afternoon.
Afternoon and sunset departures leave after lunch, by which point most of the morning fleet is heading home. You get a considerably emptier beach at Koh Madsum, better light for photographs, and on the sunset itineraries the sun going down behind the island from the water. What you give up is flat water and lively pigs.
If you have one free day and uncertain weather, take the morning boat: it has more margin if something needs rescheduling and leaves the afternoon free. If you have several days, or you have been to Koh Madsum before, the afternoon and sunset trips are the better experience.
Booking Around the Weather
Three practical points.
Book with free cancellation, which every tour on this site carries up to 24 hours before departure. In the October to December window that is not a nicety, it is the mechanism you will use.
Book early in your trip rather than late. If you are on Koh Samui for a week and put the boat trip on day six, a cancellation leaves you nowhere to move it to. Put it on day two and the rest of the week is your buffer.
And check the forecast for the sea, not the sky. A grey morning with flat water is a perfectly good Pig Island day. A bright one with a stiff northeasterly is the one that gets shortened.
Frequently Asked Questions
What is the wettest month on Koh Samui?
November, at roughly 445 mm of rainfall — nearly seven times February’s 65 mm. It is also when the northeast monsoon makes the sea roughest, so it is the month when Pig Island boat trips are most often shortened or cancelled.
Is May to September a bad time to visit Pig Island?
No. Koh Samui largely misses the southwest monsoon that soaks the Andaman coast in those months, and rainfall here runs a fairly ordinary 100 to 135 mm through that stretch. Boat trips operate normally.
What is the driest month for a Koh Madsum trip?
February, at about 65 mm. The reliable dry window runs from around the middle of January through April, with April the hottest of the four.
Do Pig Island tours run in the rainy season?
Yes, most days. Operators adjust the itinerary rather than cancelling outright — kayaking goes first, the Koh Tan reef stop second, longtail departures third. Free cancellation up to 24 hours before departure applies year-round.
Is the water cold at any time of year?
No. Sea temperature off Koh Samui sits between about 28 and 30°C every month, so water temperature is never the reason to pick one month over another.
Should I book the morning or the afternoon trip?
Morning for flatter water and more active pigs; afternoon for a much emptier beach and better light. With one free day take the morning slot for the extra rescheduling margin. With several days, the afternoon is the better trip.
Pig Island, Koh Tan and a Boat Back Before Dinner
Half-day and full-day trips from Koh Samui's south coast, with snorkelling gear, hotel transfers and free cancellation up to 24 hours before you go.
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