Koh Samui weather May brings the hottest days of the year and the return of regular rain after the dry season. It is also when the high season ends, so beaches empty out and rooms become easier to find.
This guide gives you the official averages, explains the wind shift that changes which coast is calmer, and shows how to get the most out of a hot, quieter month.
Koh Samui Weather May at a Glance
May is the start of the transition season. Rain falls on about 14 days, usually as short afternoon or evening showers, temperatures peak and the wind turns to the west.
- Rainfall
- 131.6 mm
- Rainy days
- 14.0
- Average high
- 32.9°C
- Average low
- 25.7°C
- Humidity
- 80%
- Wind
- 2.2 kn, west
These Koh Samui weather May figures are the 1991–2020 climate normals of the Thai Meteorological Department for its Ko Samui station. They describe a typical May, not a forecast for your dates, and one station stands for the whole island.
Good for
- Value and quieter beaches
- Travellers who like heat
- East-coast beach holidays
- Remote workers on longer stays
Think twice if
- You struggle in heat and humidity
- You want the driest weather (go February to April)
- Your trip is all about the west coast sea
- You dislike afternoon showers
Where Koh Samui weather May sits in the year: average rainfall per month in millimetres, Thai Meteorological Department, Ko Samui station, 1991–2020. Select a month to open its guide.
May means better value
The high season is over. Compare rates for your dates and check each room's cancellation terms.
Koh Samui Weather May: Rain and Heat
The Thai Meteorological Department's Ko Samui station records an average of 131.6 mm of rain in May over 14.0 rainy days, a clear step up from April's 8.1. The Thai weather service usually declares the start of the national rainy season in mid-May; in 2026 it did so from 15 May.
Rain in May tends to arrive as short, heavy showers in the afternoon or evening rather than all-day rain, though grey days happen.
May is the hottest month on these figures, with an average high of 32.9°C and a low of 25.7°C. Humidity averages 80%.
Koh Samui Weather May: Sea Conditions and Swimming
From May to October the Ko Samui station records mostly westerly winds, and in May they are light, averaging 2.2 knots. On breezier days the west coast catches more chop, while the east coast, Chaweng and Lamai, is often calmer.
That is the opposite of the winter months, and it is why many visitors find the east coast at its best in May. Boat trips usually run, with the odd postponement after a storm.
Swimming safety
Lifeguard cover is limited on many Samui beaches. Stay out of the water when red flags are up or when waves break hard on the shore, keep children within reach, and ask your hotel about currents on the day. A calm-looking bay can still pull.
Koh Samui Weather May: Where to Stay
With westerly winds, the east coast is the natural choice for calm swims in May. The west coast is still lovely for sunsets but can be choppier.
| Area | Coast | In May |
|---|---|---|
| Chaweng | East | Often calm sea; plenty open; quieter than high season. |
| Lamai | East | Calm water, relaxed atmosphere. |
| Bophut and Fisherman's Village | North | Walkable and lively enough. |
| Choeng Mon | North-east | Sheltered bays. |
| West coast | West | Sunsets, but more exposed to westerly wind. |
Quieter months are a good time to try a higher category of room, since availability is better. Compare every area in our where to stay in Koh Samui guide.
When you have narrowed it down, compare rooms for your exact dates on Agoda and read the cancellation terms of each rate before you pay: they differ from one offer to the next.
Koh Samui Weather May: Best Things to Do
May works for most activities. Plan outdoor time for the morning, keep the hot middle of the day for the pool, and expect a shower later.
| Activity | In May | Plan B |
|---|---|---|
| Ang Thong Marine Park | Open; usually running | Rebook after a storm |
| Snorkelling | Good on calm days | East-coast spots |
| Temples and viewpoints | Very hot by late morning | Go at 8 am |
| Na Muang waterfall | Flow picks up after rain | Skip after a heavy downpour |
| Spa, cooking class | Unaffected | — |
Boat trips usually run. If a storm passes, operators may postpone.
Making the most of short showers
Most May showers are heavy but brief. Keep a light rain jacket in your bag, plan an indoor stop for the afternoon, and use rain radar to time your next move. Our rain radar guide shows how.
Why the east coast shines
With the wind mostly from the west, Chaweng, Lamai and Choeng Mon are often calm and clear in May, the reverse of the winter pattern. It is a good month to stay on the east coast for swimming.
East coast mornings
In May, the best beach time is usually early: the light is softer, the sea on the east coast is often glassy, and the heat has not yet built. Plan a swim at 8 or 9 am, retreat to the shade by 11, and come back for a late-afternoon dip after the shower has passed. It is a rhythm many long-stay visitors settle into.
Long stays in May
May is a popular month to start a longer stay on Samui. Resorts and serviced apartments are easier to book, and some offer monthly rates. If you plan to work remotely, ask about backup power and internet, since short power cuts can follow storms.
Visiting temples respectfully
Big Buddha, Wat Plai Laem and the island's other temples ask visitors to cover shoulders and knees and to remove shoes before entering buildings. Keep a light scarf or sarong in your bag; it also helps against the midday sun.
Ang Thong National Marine Park: kayak and snorkel day trip
Usually running in May, with fewer boats than in high season. Morning departures avoid most of the afternoon showers.
Check on the listing before you book
- Pickup area and departure pier
- What happens if the park closes for weather
- Whether the national park fee is included
Powered by GetYourGuide. Price, duration and availability depend on your date.
Koh Samui Weather May: Day Trips
Samui is the hub for day trips in the Gulf of Thailand. In May, the average wind at the Ko Samui station is 2.2 knots from the west, which decides how comfortable the crossings are. Shorter trips are the safer choice whenever the forecast is borderline.
| Trip | In May |
|---|---|
| Ang Thong Marine Park | Open outside the annual closure; can close for a day in rough seas. |
| Koh Phangan | Short, usually smooth crossing. |
| Koh Tao and Koh Nang Yuan | Long crossing, usually workable; check the forecast. |
| Pig Island and the southern islands | Short trips, the easiest choice on a borderline day. |
Whatever the month, book day trips early in your stay so you can move them, and read each operator's weather and cancellation policy. Our guides to Ang Thong, getting to Koh Phangan and Koh Nang Yuan cover each trip in detail.
Koh Samui Weather May: Heat and the Start of the Rainy Season
May has the highest average maximum of the year at the Ko Samui station, 32.9°C. Combined with humidity, the heat can be tiring for visitors arriving from a European spring.
Short, heavy showers usually bring some relief in the late afternoon or evening. Plan your day around them: outdoor sightseeing in the morning, pool or spa in the afternoon, dinner after the rain.
Visakha Bucha, a Buddhist holy day that falls on the full moon of the sixth lunar month, is often in May. Temples hold ceremonies and candlelit processions, and the sale of alcohol may be restricted that day. Check the date for your year before you travel.
Koh Samui Weather May: Who It Suits
May suits travellers who prefer value and space over guaranteed dry weather.
- Couples. Quiet beaches and good-value resorts.
- Families. Possible outside school holidays; plan around midday heat.
- Snorkellers. East-coast and Ang Thong trips usually run.
- Budget travellers. Better value than the high season.
- Remote workers. Quieter cafés and easier long-stay deals.
Koh Samui Weather May: A 5-Day Plan
A plan for heat and afternoon showers.
- Day 1. Arrive, swim at Chaweng or Lamai.
- Day 2. Ang Thong day trip with a morning departure.
- Day 3. Big Buddha and Wat Plai Laem at 8 am, spa in the afternoon.
- Day 4. Beach morning, cooking class in the afternoon.
- Day 5. Na Muang waterfall, then a sunset on the west coast if the sky is clear.
Koh Samui Weather May: Prices and Crowds
May is the start of the low season, so rooms are generally easier to find and rates lower than from December to April.
Compare live prices for your exact dates rather than relying on percentages quoted online.
Koh Samui Weather May: Packing and Getting Around
Pack for heat, sun and short showers.
- Light, breathable clothing
- A compact umbrella or light rain jacket
- Reef-safe mineral sunscreen and a hat
- Electrolyte sachets
- Insect repellent
Roads can be slippery right after a shower. If you ride a scooter, slow down and avoid riding during heavy rain. If you plan to ride, read our scooter rental guide first, and keep data on your phone with an eSIM for Thailand so you can check radar and messages on the road.
Koh Samui Weather May: Health and Safety
Heat is the main health risk in May, with average highs of 32.9°C and humidity around 80%. Drink water before you feel thirsty, add electrolytes on long days out, and keep the hours between 11 am and 3 pm for shade, the pool or a long lunch.
Mosquito-borne illnesses such as dengue occur in Thailand all year and are more common in the rainy season. Use repellent, especially at dawn and dusk, and choose rooms with screens or air conditioning.
Helmets are compulsory for scooter riders in Thailand, and road accidents are the most common cause of serious injury for visitors. Ride slowly, avoid riding after drinking, and make sure your travel insurance covers scooters if you plan to ride.
Travel insurance that covers medical care and weather-related changes is worth having whatever the month.
Koh Samui Weather May: Getting Here
Most visitors arrive either by air into Samui's own airport, mainly with flights from Bangkok, or by flying or taking the train or bus to Surat Thani and crossing by ferry from Donsak to Nathon or Lipa Noi. The ferry route is usually cheaper and takes longer.
Crossings are usually smooth, with occasional delays after a squall.
Compare ferries and flights on 12Go for your dates, and see our Koh Samui ferry guide for the routes. Sea crossings usually run normally; storms can cause short delays.
Koh Samui Weather May: Booking Tips
- Read the cancellation terms on each offer.
- Book boat trips for the morning.
- Look at long-stay rates if you are staying several weeks.
- Leave a buffer day before international flights.
Booking a few weeks ahead and reading the conditions of each rate matters more than chasing the lowest headline price.
Koh Samui Weather May vs April and June
| Month | Rainfall | Rainy days | High / low | Wind |
|---|---|---|---|---|
| April | 82.9 mm | 8.1 | 31.8°C / 26.0°C | 2.6 kn, east |
| May | 131.6 mm | 14.0 | 32.9°C / 25.7°C | 2.2 kn, west |
| June | 133.6 mm | 13.1 | 32.7°C / 25.3°C | 2.3 kn, west |
May is hotter and wetter than April, and similar to June, which has almost the same rainfall with slightly fewer rainy days. To weigh every month side by side, use our best time to visit Koh Samui guide.
The bottom line on Koh Samui weather May
May is hot and quieter, with rain returning on about 14 days, mostly as afternoon showers. Stay on the east coast for calm swims, plan outings for the morning, and enjoy better value than in the high season.
Koh Samui Weather May: FAQ
Is May a good time to visit Koh Samui?
Yes for value and quiet beaches, if you can handle heat and some afternoon showers. Rain falls on about 14 days on average.
Is May the hottest month in Koh Samui?
Yes on the official averages: the average high is 32.9°C at the Thai Meteorological Department's Ko Samui station.
Does it rain a lot in May?
More than in April. The 1991–2020 average is 131.6 mm over 14.0 rainy days, usually in short showers.
Which coast is calmer in May?
Usually the east coast, because winds are mostly from the west from May to October.
Is Ang Thong open in May?
Yes, outside the annual closure period, and tours usually run.
Is May low season on Koh Samui?
Yes. The high season ends in April, so beaches are quieter and rooms easier to find.
Will it rain all day in May?
Rarely. Rain usually comes as short, heavy showers in the afternoon or evening.
Ready to book May?
Compare rooms for your exact dates. Not sure about the weather? Ask a local on WhatsApp from the menu.
See how the season continues in our June guide, or compare with April.
Sources for Koh Samui Weather May
Climate figures on this page come from the Thai Meteorological Department's 30-year climate normals. Other facts were checked on 13 November 2026 against the sources below. Weather, park rules and event dates can change, so confirm locally before you travel.
- Thai Meteorological Department: climatological data for the period 1991–2020 (Ko Samui station 48550)
- Thai Meteorological Department: forecasts and warnings
- Tourism Authority of Thailand
- Thairath: TMD declares the 2026 rainy season from 15 May
How we put this guide together
Every climate figure on this page comes from one official dataset, the Thai Meteorological Department's 1991–2020 normals for the Ko Samui station, so the May numbers can be compared fairly with every other month in our series. We do not publish rain probabilities by week, sunshine hours or sea temperatures, because no official Samui series supports them.
Dates for parks, festivals and holidays were checked against the sources listed above. Prices change daily, so we point you to live availability instead of quoting rates. We update this guide when an official date or rule changes.
Disclosure: InsideSamui may earn a commission when you book through some links on this page, at no extra cost to you. Tour listings are provided by GetYourGuide. Prices, park rules and event dates change, so always confirm before you travel.