Best Time to Visit Koh Samui

Month-by-month weather, sea conditions and festivals for the whole island — not just the park. Here's exactly when to book, and when to hold off. Updated August 2026.

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Quick Answer

February and March are the best months — driest skies, calmest seas and the clearest snorkelling water of the year, with peak visibility for both shore snorkelling and boat trips to Ang Thong. December, January and April are also excellent. The one stretch to avoid outright is October–November: the wettest, roughest weather of the year, plus the annual Ang Thong closure.

Koh Samui Runs on the Opposite Monsoon Clock

Koh Samui sits on the Gulf of Thailand side of the peninsula, which runs on the opposite seasonal pattern to Phuket and the Andaman coast. Samui's wettest, roughest months are October–December (November is the single wettest), while the Andaman coast is soaked May–October. That's why "best time for Thailand" advice built around Phuket can actively mislead Koh Samui travellers — and why Samui is one of Thailand's best beach islands during the European summer holidays (July–August), when the Andaman side is in its own monsoon.

Pоwered by GetYourGuide

Koh Samui, Month by Month

Temperatures barely move year-round (roughly 27–29°C, sea always 28°C+) — rain and sea state are the real variables.

MonthRainSea & Boat TripsCharacter
JanuaryModerate, drying outCalm, light NE winds✓ Good — peak season begins
FebruaryDriest monthCalmest of the year✓ Best all-round
MarchLow, sunniest skiesCalm, best visibility✓ Best all-round
AprilLow-moderateStill calm✓ Good — Songkran Apr 13–15
MayRising, short showersBuilding SW-monsoon swell◑ Fair — great value
JuneShort afternoon showersModerate◑ Fair — quiet, good value
JulyModerateGenerally calm on the Gulf side◑ Fair — better than Phuket now
AugustModerate, lushGenerally calm◑ Fair — good value, low crowds
SeptemberRising, cloudiest monthBuilding✕ Weak — rising cancellation risk
OctoberHeavy, ramping upRough✕ Avoid — frequent cancellations
NovemberWettest monthRoughest✕ Avoid — Ang Thong closed Nov 1
DecemberEasing through the monthImproving◑ Good after ~Dec 15 reopening
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Rainfall Figures Vary by Source

Weather aggregators disagree on exact annual rainfall totals for Samui (estimates range from roughly 1,650mm to 2,400mm a year) depending on the station and reference period used. Every source agrees on the same overall pattern, though: driest in February, wettest in October–November. Treat monthly figures as a guide, not gospel, and check a short-range marine forecast (Windy or Windfinder) before booking a boat day.

Other Experiences You Might Enjoy

Whatever week you land on, there's a good boat trip for it.

Once you've picked your dates, the standout trips are the limestone islands and Emerald Lake of Ang Thong Marine Park, the clear reefs and turtles of Koh Tao and the Koh Nang Yuan sandbar, and the easy family day to Koh Madsum (Pig Island) and Koh Tan. Basing yourself on Koh Phangan for part of the trip? Our Koh Samui–Koh Phangan ferry guide covers the crossing. Add sea kayaking, a private speedboat charter, or a sunset cruise. Live options across all of these are below.

Peak, Shoulder & Low Season at a Glance

The same four windows, framed for planning: when to book early, when to bargain-hunt.

✓ Peak

December – February

Perfect weather, highest prices and biggest crowds. Christmas–New Year and Chinese New Year are the most expensive weeks of the year — book hotels 6–8 weeks ahead.

◑ Shoulder

March – June

Excellent-to-good weather at roughly 20–30% lower prices than January, with thinner crowds. Arguably the smartest value window of the year.

◑ Variable

July – September

A reliable Gulf-side summer beach option while the Andaman coast is in its own monsoon, cooling toward the cloudiest month, September.

✕ Low

October – November

The wettest, roughest stretch of the year. Lowest prices and fewest tourists, but the highest chance of washed-out boat days.

The Best Month Depends on Why You're Going

Weather quality is one input — your travel style matters just as much.

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General Beach Holiday

December–April, best of all February–March — dry, calm and sunny roughly 8 hours a day in March.

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Boat Trips & Island Hopping

February–April are the safest windows for glassy conditions to Ang Thong and Koh Tao. Most operators cancel above roughly 1.5m waves.

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Snorkelling Visibility

Best February–April, when park visibility often reaches 15–20m. See our snorkelling tours guide for spot-by-spot conditions.

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Summer-Holiday Families

July–August. Choose Samui over Phuket for this stretch — the Gulf side is markedly sunnier and calmer during the Andaman coast's own monsoon.

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Budget & Quiet Travellers

May, June or September for the lowest prices and thinnest crowds, accepting the odd short shower.

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Hard Avoid

October–November for any beach or boat-based plan — pair a fixed trip in this window with an Andaman-coast leg (Phuket, Krabi) instead, since it's dry there.

October–November: The Months to Avoid

October and November are the worst months for a beach or boat holiday on Koh Samui: the heaviest rain, roughest seas, frequent ferry disruption and multi-day cloudy spells. November is statistically the wettest month, and the Gulf's tropical-cyclone risk window runs roughly mid-October to late December, when low-pressure systems can bring flooding to Surat Thani province.

Two knock-on effects worth planning around:

  • Ang Thong Marine Park closes annually from November 1 to around December 15 for monsoon safety — see our Ang Thong best-time guide for the exact closure details and what to book instead.
  • Inter-island ferries run less reliably. Crossings to Koh Phangan and Koh Tao see occasional cancellations in this window — check current sailings in our Koh Samui–Koh Phangan ferry guide before booking a fixed-date crossing.
    • Calm sea conditions for kayaking near Ang Thong Marine Park during the dry season
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    Wave & Wind Thresholds

    A wave forecast above ~1.5m or wind over 15–20 knots typically means boat tours get cancelled or rescheduled. Keep a flexible backup day if you're travelling October–December.

    Festivals & Holidays That Move Prices

    Big dates to plan around, whether you want to join in or avoid the crowds.

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    Songkran (Thai New Year)

    April 13–15 nationally; Samui's water-fight celebrations run roughly April 10–15 along Chaweng Beach Road. Lively but crowded and pricier.

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    Full Moon Party

    Monthly on nearby Koh Phangan — spikes ferry and accommodation demand island-wide. See our ferry guide for 2026 dates and booking tips.

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    Christmas & New Year

    Dec 23–Jan 2 is the highest-demand, highest-price stretch of the year across the island.

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    Chinese New Year

    Late January or early February brings another price and crowd spike, right in the middle of the best-weather window.

    Match Your Tour to Your Season

    Live availability updates in real time — good for a quick reality check on what's actually running.

    🥇 Peak Season (Dec–Apr) — Kayak, Snorkel & Lunch

    The flagship Ang Thong day tour, at its best when seas are calmest — snorkelling, kayaking and the viewpoint hike in one trip.

    Check Prices & Availability →

    🚢 Shoulder Season (May–Sep) — Stable Big-Boat Cruise

    A spacious, more stable ride for the occasional choppier shoulder-season day — a comfortable pick if seas are up.

    Check Prices & Availability →

    🐷 Any Season — Easy Family Day (Pig Island & Koh Tan)

    Sheltered, close-to-shore waters that stay calmer even in shoulder-season swell — a dependable backup on marginal weather days.

    Check Prices & Availability →

    🐢 Feb–Apr for Peak Visibility — Koh Tao Day Trip

    The clearest water in the Gulf, best in the dry-season window. Full details in our Koh Tao day trip guide.

    Check Prices & Availability →

    Booking Smart Around the Seasons

    General Booking Windows

  • Peak season (Dec–Feb): book hotels 6–8 weeks out; boat tours can usually wait until 48–72 hours ahead once you can check the forecast.
  • Shoulder/low season (May–Sep): book 24–48 hours ahead and always choose free-cancellation tours.
  • Fixed dates in Oct–Nov? Build a flexible, indoor-friendly itinerary or pivot boat days to the Andaman coast, which is dry then.

    • Signs a Tour Will Get Cancelled

  • Wave forecast above ~1.5m or wind over 15–20 knots: most operators cancel or reschedule — keep a backup day.
  • An active tropical low in the lower Gulf (mid-Oct–late Dec): postpone crossings and check Thai Meteorological Department marine warnings.
  • Pack for both anyway: a light rain jacket and reef-safe sunscreen both earn their place — see the full packing list.

    • Common Question

    February and March are the best months — the driest, sunniest and calmest weeks of the year, with the clearest water for snorkelling and diving. December, January and April are also very good. Avoid October and November, which bring the heaviest rain, the roughest seas and the annual Ang Thong Marine Park closure. March–May offers near-peak conditions at noticeably lower prices, and July–August is a smart pick for a Gulf-side summer beach holiday since Koh Samui runs on the opposite monsoon clock to Phuket. See our Ang Thong-specific best-time guide for exact closure dates.

    Ready to Lock In Your Dates?

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