A clear, month-by-month guide to Surat Thani's Gulf-coast climate - including the October-December northeast-monsoon season that's the real reason ferries to Koh Samui, Koh Phangan and Koh Tao get cancelled - plus what to pack.
Surat Thani, the mainland Gulf-coast gateway to Koh Samui, Koh Phangan and Koh Tao, has a tropical, near-equatorial climate with fairly steady temperatures year-round - but its rain pattern is genuinely different from most of Thailand. A drier, hotter stretch (February-April) gives way to routine southwest-monsoon rain (May-September), before the real story: a sharp northeast-monsoon deluge (October-December) that brings the heaviest rain of the year and is the single biggest reason ferry crossings to the islands get disrupted. If your trip depends on a reliable island crossing, the Don Sak ferry piers are the thing to plan around most carefully.
Surat Thani's closest thing to a dry season. February is the driest month of the year by far, and April is the hottest, with daytime highs pushing toward 33°C. Humidity is still noticeably higher than inland cities like Khon Kaen or Chiang Mai year-round, but this stretch is the most comfortable and the most reliable for ferry crossings to Koh Samui, Koh Phangan and Koh Tao.
The regional southwest monsoon brings frequent but generally moderate rain - 14 to 17 rainy days most months, usually as afternoon or evening storms rather than sustained all-day downpours. It is wetter and more humid than the Feb-Apr stretch, but ferry disruption is still the exception rather than the rule in this period.
This is Surat Thani's real wet season and its defining weather story: the northeast monsoon funnels heavy, sustained rain and rough seas into the Gulf of Thailand, with October and November each averaging well over 270mm of rain across 18-20 rainy days - roughly double the wettest months of the mid-year southwest monsoon. Cooler air also drops daytime highs into the high 20s. This is when ferry and speedboat operators serving Koh Samui, Koh Phangan and Koh Tao most often suspend sailings for rough seas, monsoon troughs and the occasional tropical depression forming over the Gulf.
Approximate daytime highs and overnight lows and typical rainfall for each month, based on compiled long-term averages (1991-2021). Figures are climate averages - individual years vary, and the northeast-monsoon intensity in particular swings year to year. October and November are each around 270-280mm on average - roughly double the wettest months of the mid-year southwest monsoon - while February is the driest month of the year.
| Month | High | Low | Rain | Verdict |
|---|---|---|---|---|
| January | 29° | 22° | Moderate | Warm, still some rain |
| February | 31° | 22° | Very low | Driest month |
| March | 33° | 24° | Low-moderate | Hot, drying out |
| April | 33° | 25° | Moderate | Hottest month |
| May | 32° | 25° | Moderate-high | Monsoon onset |
| June | 31° | 25° | Moderate | Regular storms |
| July | 31° | 24° | Moderate | Regular storms |
| August | 31° | 24° | Moderate-high | Consistently wet |
| September | 30° | 24° | High | Wetter, building |
| October | 29° | 24° | Very high | Ferry-risk season begins |
| November | 29° | 23° | Highest | Peak ferry-disruption risk |
| December | 28° | 23° | High, easing | Coolest, still unsettled |
Temperatures in °C. Figures are averages for Surat Thani city; individual years vary.
For the most comfortable weather and the most reliable ferry crossings to Koh Samui, Koh Phangan and Koh Tao, come between February and April - the driest, hottest and calmest stretch of the year. May to September brings routine but generally moderate southwest-monsoon rain, with ferry disruption still the exception. October to December is Surat Thani's defining weather season: the northeast monsoon brings the heaviest, most sustained rain of the year and the real risk of ferry and speedboat suspensions to the islands, so if your trip timing is flexible, it's worth avoiding this window - or at minimum building in a spare day or two around any island crossing.
| Season | What to bring |
|---|---|
| Drier stretch (Feb-Apr) | Light, breathable clothing, sunscreen and a hat - this is Surat Thani's most comfortable and most ferry-reliable stretch, though humidity never fully disappears. |
| Routine monsoon (May-Sep) | A compact umbrella or rain jacket for regular afternoon storms, plus quick-dry footwear. Ferry disruption is still uncommon in this period, but check forecasts before island day trips. |
| Ferry-disruption season (Oct-Dec) | A proper rain jacket, dry-bag protection for electronics if you're crossing by ferry, and schedule flexibility - build in a spare day or two around any Koh Samui/Phangan/Tao crossing, and check operator status the morning of travel rather than assuming your booked sailing will run. |
February to April is Surat Thani's driest, most reliable stretch for both comfortable weather and dependable ferry crossings to Koh Samui, Koh Phangan and Koh Tao. December and January are cooler and calmer than the October-November peak but still carry some monsoon tail, so build in flexibility if your trip depends on a ferry crossing.
Surat Thani's Gulf-coast position means it takes the brunt of the northeast monsoon from roughly October to December, which regularly brings rough seas, monsoon troughs and occasional tropical depressions to the Gulf of Thailand. In November 2025, for example, multiple ferry and speedboat operators (including Lomprayah, Songserm and Lotus Ferry) suspended sailings on the Surat Thani-Koh Samui-Koh Phangan-Koh Tao routes for several days due to exactly this kind of weather system.
Yes, meaningfully. Most of Thailand - Bangkok, Phuket, inland cities like Khon Kaen and Chiang Mai - sees its wettest months during the May-October southwest monsoon. Surat Thani, on the Gulf coast, gets its heaviest rain later, in October and November, driven by the northeast monsoon. It's worth knowing this if you're comparing weather advice written for the rest of Thailand.
Surat Thani's tropical, near-equatorial climate keeps temperatures fairly consistent year-round, with April as the hottest month (highs around 33°C) and December as the coolest (highs around 28°C). Humidity stays relatively high in all seasons compared with inland Thailand.
Light, breathable clothing and sun protection year-round, plus a proper rain jacket and dry-bag protection for electronics if you're travelling October-December, when ferry crossings to the islands are most likely to be disrupted by rough seas.
Climate averages compiled from long-term (1991-2021) data; the November 2025 ferry-suspension example is a real, recent, multi-source-corroborated event cited to illustrate typical northeast-monsoon disruption, not a permanent schedule -- always confirm current sailing status directly with your ferry operator.
Whether you're passing through to the islands or settling in mainland Surat Thani, match the right area to how you want to live, then browse residences there.
General climate information based on long-term averages (climate-data.org, 1991-2021); actual weather and ferry schedules vary year to year - check a current forecast and your ferry operator's status before you travel. Hero photo by Pok Rie on Pexels.