Gulf weather, not Andaman weather
Driest month
February
64.3 mm mean rainfall
Warmest mean high
May
32.9 °C by day
Wettest month
November
444.6 mm mean rainfall
Annual mean temperature
28.0 °C
Tropically warm all year
The quick answer
Choose February to April for the strongest statistical chance of dry beach and boat days. June to August is a useful UK-summer option, with more cloud and local showers but before the main Gulf rain peak. October and November need the most flexibility; TMD records November as the wettest month by a wide margin.
Driest starting point
February–April
UK-summer option
June–August
Most flexibility
October–December
Official climate normals
These figures are averages from TMD station Ko Samui 48550 for 1991–2020. Rainfall is the monthly total; a measurable rain day does not automatically mean an all-day washout.
| Month | Mean high | Mean low | Rainfall | Rain days | Travel outlook |
|---|---|---|---|---|---|
| January | 29.0 °C | 24.2 °C | 126.8 mm | 11.1 | Drying out |
| February | 29.4 °C | 24.9 °C | 64.3 mm | 5.6 | Driest month |
| March | 30.4 °C | 25.4 °C | 115.8 mm | 5.9 | Dry and warm |
| April | 31.8 °C | 26.0 °C | 82.9 mm | 8.1 | Dry and hot |
| May | 32.9 °C | 25.7 °C | 131.6 mm | 14.0 | Hotter, more showers |
| June | 32.7 °C | 25.3 °C | 133.6 mm | 13.1 | Useful summer option |
| July | 32.3 °C | 25.1 °C | 117.0 mm | 14.3 | Workable with showers |
| August | 32.4 °C | 25.1 °C | 102.2 mm | 14.5 | Summer with a buffer |
| September | 31.9 °C | 24.8 °C | 117.5 mm | 15.0 | Transition month |
| October | 30.6 °C | 24.3 °C | 294.9 mm | 19.3 | Rain peak begins |
| November | 29.7 °C | 24.1 °C | 444.6 mm | 18.7 | Wettest month |
| December | 29.3 °C | 24.0 °C | 263.1 mm | 14.2 | Still changeable |
The lower Gulf receives its strongest rain later in the year. July and August can therefore be useful on Samui while the Andaman coast is often wetter and rougher.
TMD counts a day with measurable rainfall as a rain day. It may include dry usable hours, but the statistic never promises that every shower will pass quickly.
For Ang Thong and other boat days, wind, waves and thunderstorms matter more than one weather-app rain percentage.
Choose the season deliberately
February has the lowest mean rainfall. March and April have relatively few rain days, while daytime heat climbs towards April.
Best for: Beach time, Ang Thong, island combinations and a first Samui trip.
Trade-off: This is a popular window. Secure the stay that matters and schedule active hours before the hottest part of the afternoon.
Koh Samui receives showers and more cloud, but the main rain peak has not arrived. July and August are often more practical here than on the Andaman coast.
Best for: UK school holidays, a slower pace and a Koh Phangan or Koh Tao combination.
Trade-off: Measurable rain days are more frequent. Keep boat plans movable and let current sea conditions overrule the calendar.
Rain rises sharply from October. November is the wettest month; December remains changeable and January usually moves back towards drier conditions.
Best for: Wellness, food, longer stays and travellers able to exchange complete days.
Trade-off: Boat departures, sea views and beach time are less predictable. Book flexibly and take local flooding seriously.
One shower is not the whole day
A tropical shower can pass quickly, but rain in October and November can also persist. Look for usable windows and sea conditions, place the boat day early and make land days valuable in their own right.
Different trips need different months
February–April
The driest months give the best statistical starting point. Still check current wind and waves before Ang Thong or a Koh Tao crossing.
June–August
Samui is often a stronger Thai coast choice than the Andaman side in these months. Expect heat, cloud and local showers rather than guaranteed blue skies.
May–September
The island is lush and the main rain peak is still ahead. Alternate beach time with temples, food, inland nature and wellness.
May, June or September
Shoulder periods may produce useful room options. Check cancellation and change terms instead of choosing on a displayed rate alone.
Pack with purpose
Koh Samui packing listLight, breathable clothing — Add a modest layer for temples, boat wind and strong air conditioning.
Compact rain poncho — Useful in a day bag for a sudden shower or exposed transfer.
Check the current poncho price on AmazonSun hat and covering layer — UV exposure remains relevant through thin cloud and on the water.
Insect repellent — Practical around green inland areas and at dusk; follow the product directions.
Check current insect-repellent options on AmazonWaterproof drybag — Separates a phone, camera and dry clothing from spray on a boat day.
Check the current drybag price on AmazonQuick-dry towel — Compact for beach and boat days and easier to reuse after a shower.
Check the current travel-towel price on AmazonAs an Amazon Associate, we earn from qualifying purchases. You pay nothing extra; availability and delivery vary by country.
Complete Thailand packing listKeep the plan flexible
Plan A
Use the calmest sea window for the main boat day and place it early enough to move.
Plan B
Combine Wat Plai Laem, a long lunch and Fisherman’s Village when short showers pass.
Plan C
A cooking class, spa or food-led day remains worthwhile when the rain genuinely persists.
Book smart: Put the most important boat day early in the stay and keep one substantial island day plus one sheltered wet-day plan in reserve. Prefer conditions that allow a change when sea conditions deteriorate.
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DFS People Also Ask
February to April gives the driest statistical starting point in the TMD 1991–2020 normals. June to August can also work well for a UK-summer trip. The right month still depends on heat tolerance, budget and how much flexibility your boat plans have.
Koh Samui’s clearest rainfall peak is later than on the Andaman coast. Rain rises sharply in October, peaks in November and remains elevated in December. September is a transition month and January normally moves back towards drier conditions.
November is the wettest month at TMD station Ko Samui for 1991–2020, with 444.6 mm mean rainfall. October averages 294.9 mm and December 263.1 mm.
Travellers who need predictable beach and boat conditions take the largest statistical weather risk in October and November. That is not a ban on travel: it means flexible bookings, substantial land alternatives and current marine checks matter much more.
August is a workable month. TMD records 102.2 mm mean rainfall and 14.5 rain days, while the main Gulf rain peak arrives later. Expect heat, cloud and local showers, and check wind and sea state for every boat departure.
The climate averages are close: July records 117.0 mm rainfall and August 102.2 mm, with similar temperatures and rain-day counts. That small statistical difference cannot predict one holiday, so choose around dates and value, then use the current forecast for daily plans.
December can work for a flexible island stay, but it is not statistically one of the driest months: TMD records 263.1 mm mean rainfall. Travellers prioritising guaranteed-looking beach imagery should avoid promises and check the current pattern close to departure.
Yes, but rainfall is uneven across the year. February is the driest month in the station normals, while October to December carry the strongest rainfall signal. A rain-day count records occurrence, not whether every hour was wet.
Use timing and trip style rather than a universal winner. Koh Samui often has a more useful rainfall pattern from June to August; Phuket can be more attractive in other windows. Compare current conditions, coast access, flights and the experiences you actually want.
Mosquitoes are present in a tropical island environment, especially around vegetation, standing water and dusk. Use practical bite prevention such as appropriate clothing and repellent, and seek current professional health advice for personal medical questions.
Verder plannen
Compare coasts, island rhythm and a practical multi-day route.
Lees de gids
Choose between temples, inland nature, beaches and Ang Thong.
Lees de gids
Compare Chaweng, Lamai, Bophut, Maenam and the quieter west coast.
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Bronnen & methode
We do not generate a long-range weather forecast. The table uses official climate normals; for the coming days, use the current Thai Meteorological Department forecast.
Thai Meteorological Department
Authoritative monthly temperature, rainfall and rain-day normals for station 48550.
Thai Meteorological Department
Official current forecast; climate normals are not a forecast.
Tourism Authority of Thailand
Official island and destination context.
Kuoni
Current UK-English competitor and month-intent coverage reviewed through DFS.
The Koh Samui Guide
Detailed local editorial interpretation reviewed through DFS; official TMD data controls the table.
Climates to Travel
Comparative monthly climate structure reviewed through DFS.
Let us know how we can improve this travel guide.
Complete your route
A good itinerary connects what you want to see with where you stay and the season in which you travel. Start with the best things to do in Koh Samui, compare it with the best hotels in Koh Samui and use our practical Thailand travel guides to align the practical details.
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