- From about November to January the north-east monsoon can make the Gulf of Thailand rough, so a route may change or a trip may be postponed.
- Ang Thong National Marine Park is usually closed every year from 1 November to 15 December, and no Ang Thong trips run on those dates.
- The captain makes the final call on the day, and wind and sea state matter far more than rain on its own.
- Short routes south of Samui tend to hold up best, such as a 4-hour trip to Koh Tan and Koh Madsum on Victoria for ฿25,000.
- Book your trip early in your stay and keep spare days, because a boat day can move but a flight home cannot.
It is 7 am, rain is hammering your hotel balcony, the boat is booked for 9, and the group chat is already asking whether the day is off. That is the real question behind every Koh Samui boat trip in the rainy season, and the honest answer is more often "the plan changes" than a simple yes or no.
I would rather tell you how it works than sell you a sunny picture. Some rainy-season days at sea are lovely, some are cancelled, and quite a few end up on a different route from the one you booked.
Does a Koh Samui boat trip in the rainy season actually go ahead?
Often yes, but not always, and not always to the place you planned. From about November to January the north-east monsoon can make the sea in the Gulf of Thailand rough, and trips may change route or be postponed.
Rain and rough water are two different problems, and people mix them up. A warm downpour with a flat sea is an inconvenience. A dry, bright day with a strong onshore wind can be far worse for a boat.
So do not judge the day from your balcony. A grey sky over Chaweng tells you very little about the water on the south side of the island, and a clear sky tells you very little about the crossing to Koh Tao.
There is one fixed date to plan around. Ang Thong National Marine Park is usually closed every year from 1 November to 15 December, so no Ang Thong trips run in that window, however good the weather looks. Check the opening date again if you plan to go right after it.
For the wider calendar, the month-by-month guide to boat trips covers the whole year. This article is only about the difficult stretch and how to get through it.
What is the weather really like during the north-east monsoon?
Expect variety rather than constant storms. A typical monsoon stretch mixes bright mornings, short heavy showers, whole grey days and spells of steady wind that build a swell on the Gulf side.
The showers are often the easy part. They arrive fast, soak everyone and move on, and the sea can stay perfectly manageable. Under a canopy it is warm, and many guests end up enjoying it.
The harder part is a run of days with strong wind from the north-east. It pushes waves against the exposed coasts, and the sea can stay lumpy for a while even after the wind drops. That leftover swell is what catches people out on a calm-looking morning.
A few more things change at this time of year, and it is better to hear them from me now than on the boat:
- Water clarity can drop after heavy rain, so snorkelling may be cloudier than in the photos you saw.
- Beaches can collect driftwood and rubbish that the waves bring in, and this varies a lot from one week to the next.
- Pig Beach and other shore stops depend on how safely the boat can get close, so a stop may be shorter or skipped.
None of this makes the season a write-off. It simply means you should arrive expecting a day that is flexible, not a day that matches the brochure.
How do captains decide whether a boat goes out?
The captain makes the decision, based on wind, swell and the forecast for the specific route, and safety comes before everything else. A guest cannot overrule a captain who says the sea is not safe, and no good agency should try.
The question is rarely just "go or stay". Usually it is: can this boat, with this group, do this route, and get home comfortably in the afternoon? A crossing that is fine at 9 am may be unpleasant by 3 pm if the wind builds.
The answer can also differ between boats on the same morning. A long-tail with a small open hull and a large catamaran do not face the same sea, and a route that is fine for one may be wrong for the other. So if one boat stays in, it is still worth asking the manager whether another boat or a shorter route could work on that date, as availability and conditions allow.
Who is on board matters too. A captain may be happy to run a lively crossing with four fit adults, yet choose something gentler for a family with small children or a grandmother who dislikes waves.
When there is doubt, you will usually hear about it the evening before or that morning. Keep your phone on and check WhatsApp, because this is how last-minute changes reach you.
Which routes still work when the sea is rough?
Short routes close to Samui and away from the wind tend to work best, and long open crossings are the first to go. In a north-east wind the south of the island is often more sheltered than the east coast, though this is a rule of thumb and not a promise.
Here is how I would rank the main routes for an unsettled week. The prices are per boat for a named example, not per person.
| Route | In the monsoon | Example |
|---|---|---|
| Koh Tan and Koh Madsum | Usually the safest bet: short and south of Samui | Victoria, 4 hours, ฿25,000 |
| Koh Som or Koh Mad Lang | Short, but the north side can catch the wind, so ask first | Vickey, morning half day, ฿21,000 |
| Koh Phangan | A short hop, with the sheltered side chosen on the day | Pearl, 8 hours, ฿38,000 |
| Around Koh Samui | Beautiful, but one coast takes the swell, so it may be shortened | Pearl, 8 hours, ฿39,000 |
| Ang Thong | Closed 1 November to 15 December; a long day after it reopens | Pearl, 8 hours, ฿39,000 |
| Koh Tao and Koh Nang Yuan | Long open water: usually the first route to be dropped | Pearl, 8 hours, ฿41,000 |
My honest opinion: do not book Koh Tao as your only boat day in the monsoon. It is a wonderful trip in the right conditions, but a long crossing in a lumpy sea is hard work, and it is the plan most likely to fall through.
If you want a safe first choice, look at Koh Tan and Koh Madsum. Koh Madsum is the island known as Pig Island, the trip is short, and the boats that run it come in every size and budget.
After the park reopens, Ang Thong by private boat is possible again, but late December can still be unsettled. I would keep it for a day when the forecast looks good, not lock it to your last free date.
Which boat makes sense on an unsettled day?
Choose shelter and a short route before you choose style. The two hulls of a catamaran give more stability and space, and a boat with a real saloon gives you somewhere dry to sit when a shower comes through.
A speedboat is the most flexible option, because it covers distance fast and can use a short weather window. The downside is that you feel every wave at speed, so it suits people who do not mind a bumpy ride.
Long-tails are the cheapest way to get out, from ฿3,000 for 1-2 people to Koh Tan and Koh Madsum. They are also low and open, so in the monsoon I would see them as a calm-day option and accept that they may not run.
Motor yachts and larger catamarans have indoor space, which matters on a showery day. You pay more for that: Princess 42 starts at ฿77,000 and Coco Paradise at ฿45,000, so only spend it if comfort is the reason for the trip.
Pearl suits small groups who want a fast boat with hotel transfer included, Victoria suits an easy half day to the southern islands, Blue Coco suits families who want cabins and a saloon, and Hilux suits groups who like fishing and leave from the west side.
Think about the pier as well. Victoria and Nina leave from Thong Krut on the south coast, the long-tails leave from Thong Krut Pier too, and Hilux is moored on the west side. Scarlet leaves from Choeng Mon or Bang Rak in the north, so ask how that coast looks on your date.
What happens if your trip is postponed or changed?
Usually the first conversation is about moving the route or the date, not about giving up. Ask for the exact rule for your boat before you pay anything, because the terms are not identical across every boat.
One clear example is the long-tail. A cancellation or no-show on the day costs 100% of the tour price, yet no cancellation fee is charged when extreme weather, meaning heavy rain or strong wind, prevents the trip.
Route changes are common and worth accepting. Nina's terms say plainly that the route can change depending on the weather. If the captain offers Koh Tan instead of the plan you wanted, that is usually good judgement and not a downgrade.
Keep in mind the difference between a captain's decision and your own. Deciding at breakfast that you do not like the clouds is not the same as a boat being stopped by the weather, so talk to the manager before assuming anything.
A request on the site is free and non-binding, and no payment is taken at that stage. A manager then confirms the date and final price, which is the right moment to ask your weather questions.
How can you book flexibly in the rainy season?
Book early in your stay, keep spare days behind it and agree on a plan B route in advance. These are the habits that save the most trips:
- Do not leave it for your last day. Aim for the first half of your holiday, so there is room to move the date.
- Avoid booking the day before a flight. Even if the trip runs, a delayed return adds stress you do not need.
- Ask about plan B when you book. "If Koh Phangan is rough, where would the boat go instead?" is a perfectly normal question.
- Choose a boat with short programmes. Blue Coco has a morning half day for ฿36,000, and Nina has one for ฿29,000, which helps if the afternoon looks doubtful.
- Prefer morning departures when the choice exists, as the wind often builds later, though not every day follows that pattern.
- Give a working WhatsApp number, and check it the evening before and first thing in the morning.
- Tell the manager about small children, older guests or anyone who gets seasick, so the captain can plan for them.
You can start with a date, group size and a rough idea on the request form, and mention that your dates are flexible. Being open about that makes it easier to find a good day.
What should you bring on a rainy-season boat day?
Pack as usual, then add protection for anything that must stay dry. The sun can still burn through thin cloud, so keep the sunscreen in the bag even on a grey morning.
- A dry bag or a waterproof phone pouch.
- A light rain jacket or a thin long-sleeved layer, because wet and windy can feel cool on the way back.
- Shoes with grip for wet decks and piers.
- Seasickness tablets, taken before departure and not after you start to feel bad.
- A spare set of dry clothes for the transfer back to the hotel.
The full list is in the boat trip checklist. On the morning itself, eat something light, read the manager's last message and trust the captain's call, even if the sky at your hotel tells a different story.
Questions and answers
When is the rainy season on Koh Samui?
The wettest and windiest part usually falls from about November to January, when the north-east monsoon affects the Gulf of Thailand. It does not mean rain all day, every day. Conditions vary from week to week, so treat any forecast as a guide and not a guarantee.
Can I visit Ang Thong in November?
Usually not. Ang Thong National Marine Park is usually closed every year from 1 November to 15 December, and no Ang Thong trips run then. Later in December it can reopen, but the sea can still be unsettled.
Is it safe to take a boat trip when it is raining?
Rain alone is rarely the problem. The captain looks at wind, swell and the route, and will not go if the sea is unsafe. A warm shower on a calm sea is usually just a wet half hour.
Will I get seasick more easily at this time of year?
You might, because the sea can be lumpier than in the calm months. Choose a short route, take a tablet before you leave and stay on deck looking at the horizon. Tell the manager early if someone in the group is prone to it.
Is the snorkelling still good in the monsoon?
It can be, but expect less clear water after heavy rain or strong wind. On a poor day it may be cloudy enough that the guide suggests swimming or another stop instead. Do not make snorkelling the only reason for a monsoon trip.
Do I pay anything when I send a request?
No. The request is free and non-binding, and no payment is taken at that point. A manager confirms the date and the final price, and that is the time to ask how weather changes work on your boat.
Is a sunset cruise a good idea in the rainy season?
It can be a smart choice, since it is short and you can often decide closer to the day. Victoria runs a 2.5-hour sunset cruise to Koh Tan for ฿21,000. The sunset itself is not guaranteed under cloud, but a gap in the weather can be very pretty.
Ready to choose your boat?
Every boat page shows the routes, prices and what is included. The booking request is free: a manager checks the boat is free on your date and confirms the price.
Updated 15 November 2026. Prices can change: the boat page always shows the current price.
