Koh Samui Weather Month-by-Month: What Each Month Really Feels Like
Twelve months, twelve moods: exactly what Samui's sky, sea, and prices do all year long.
- February is the driest, sunniest month; March brings the calmest seas for boat trips.
- November is the wettest month, and Ang Thong closes from November 1 to December 15.
- May, June, and September offer warm weather, small crowds, and great-value hotel rates.
- Budget for compulsory Christmas and New Year's Eve gala dinners at many resorts.
Here's the best-kept secret about Koh Samui weather: summer never leaves. The sun shows up all twelve months, the sea stays bathwater-warm, and every month has its own personality. After almost a decade here, I know exactly what each one brings, from the breezy blue days of February to the jungle-green glow of late year. Here's the real lowdown, so you can pick the Samui that fits your trip.
Samui Weather by Month: The Quick Version
The weather in Koh Samui runs on a different calendar than Phuket and the Andaman coast, which catches plenty of first-timers off guard.
- Dry and breezy (late December to March): The sunniest stretch, with February the star.
- Hot (April to May): Highs around 91°F. Glorious, but sweaty.
- Mixed (June to September): Sun most days, with short showers.
- Rainy season (October to mid-December): The island's true monsoon, peaking in November.
Daytime highs barely budge (mid-80s to low 90s°F), so rain is the variable that matters.
January: Breezy Blue Skies (With a Wildcard)
- Weather: 84-86°F days, about 75°F nights; roughly 3.5-5 inches of rain over 6-11 days
- Crowds and prices: High, especially right after New Year's
The northeast breeze keeps things comfy, and by mid-month most days are gorgeous. Early January can still throw a curveball, though: in 2017 an unseasonal storm flooded roads and delayed flights mid-peak season. If Chinese New Year lands late in the month, catch the lion dances at the Chinese temple near Maenam pier.
February: The Most Reliable Month of the Year
- Weather: 84-86°F days; about 1.5 inches of rain over just 3-5 days, plus 9 hours of daily sunshine
- Crowds and prices: Very high, and one of the priciest months
This is the safest bet for a beach vacation, with an 82°F sea and air that isn't sticky yet. The one wildcard is wind: in February 2026, Chaweng and Lamai flew red flags for a few days with 3-6 foot waves. On days like that, I drive west and swim at Lipa Noi instead.
March: Peak Beach Season Turns Up the Heat
- Weather: 86-89°F days; around 2 inches of rain over only 4-5 days
- Crowds and prices: High, easing late in the month
March has the fewest rainy days and the least cloud cover of the year, and once the breeze settles, the sea often goes glassy. It's my favorite month for Ang Thong boat days and early snorkeling at Coral Cove. Humidity starts creeping in by the last week.
April: Hot, Hotter, Songkran
- Weather: 90-91°F days; about 3 inches of rain over 8 days, with the sea up to 86°F
- Crowds and prices: Moderate, spiking around April 13-15
The midday sun means business. Mid-month, Songkran (Thai New Year) turns the island into a giant water fight. Chaweng Beach Road and Soi Green Mango go full-on, Maenam and Bophut stay family-friendly, and temples like Wat Plai Laem hold traditional water blessings.
Ted's Tip
To enjoy Songkran without getting blasted by a pickup full of teenagers with a water cannon, base yourself in Maenam or Bophut and pop into Chaweng for one wild afternoon. Seal your phone in a waterproof pouch before leaving the hotel (not after the first bucket), and park the scooter for all three days.
May: Hot, Quiet, and Great Value
- Weather: 90-92°F days (neck and neck with April for hottest); around 5 inches of rain over 16-17 days
- Crowds and prices: Low, with real deals appearing
Afternoon storms roll in, dump hard for 20 minutes, and cool everything off, which feels like a gift in this heat. In late May, the Samui Regatta brings international yachts racing off Chaweng Beach (the 2026 edition ran May 23-30).
June: Lush, Quiet, and Underrated
- Weather: About 88°F days; around 4 inches of rain over roughly 16 days
- Crowds and prices: Low
While Phuket gets hammered by the southwest monsoon, Samui sits largely sheltered behind the mainland. Expect sunny mornings, short storms, and deep-green hills. It's also fruit season, so watch for durian and mangosteen at roadside stalls.
July: The Summer Crowd Rolls In
- Weather: About 88°F days; 3.5-5.5 inches of rain over 14-17 days, usually in short bursts
- Crowds and prices: Moderate to busy, with rates often 10-20% above June
European and Asian families arrive on summer vacation, creating a mini peak season. The weather is June's twin, which makes Samui one of the best Thai beach picks during school break.
August: Family Season in Full Swing
- Weather: About 88°F days; 4-5 inches of rain over 14-17 days
- Crowds and prices: Busy, with prices climbing
Afternoon showers are common, but they're usually over before you finish a coconut shake. Skies run cloudier on average, which sunburn-prone shoulders may appreciate. Families stay until the last week, then the island exhales.
September: The Quiet Secret
- Weather: About 88°F days; 5-6 inches of rain over 16-21 days, cloudier late in the month
- Crowds and prices: Low, with rates often 30-40% below peak
With kids back in school, the beaches are yours. The first half is usually lovely, while the second half gets moodier. Bonus: Na Muang finally looks like a proper waterfall again (my Na Muang waterfalls guide covers the jungle swim).
October: A Month of Two Halves
- Weather: About 86°F days; around 10 inches of rain, with 19-20 rainy days
- Crowds and prices: Very low
October often starts hot and sunny. By the last week or so, the northeast monsoon usually arrives, the sea turns choppy, and boat trips start getting canceled. It's the start of the rainy season in Koh Samui, and some small beach bars close for renovations or staff breaks.
November: The Real Rainy Season
- Weather: About 84°F days; the wettest month, averaging roughly 12-18 inches of rain over about 19 days
- Crowds and prices: Minimal, with some of the year's cheapest hotel rates
Storms can last days instead of 20 minutes, waves on the east and north coasts can top 6 feet, and ferries to Koh Tao and Koh Phangan get canceled when the sea gets angry. Ang Thong Marine Park also closes every year from November 1 to December 15. The upside is bargain rates, an emerald island, and storms that put on a real show from a covered balcony. My rainy-day guide has plenty of backup plans.
Ted's Tip
If November is your only window, leave a buffer day between your last ferry or island flight and your flight home. Samui's microclimates are real, too: when one bay is getting soaked, another is often dry, so a rental car (not a scooter on slick roads) lets you chase the sunshine.
If you're traveling in monsoon season, it's worth reading my guide to the best travel insurance for Koh Samui before you book.
December: From Soggy to Spectacular
- Weather: About 84°F days; around 6-7 inches of rain over roughly 13 days, mostly early in the month
- Crowds and prices: Peaking at Christmas and New Year's, making it the priciest month of the year
December usually starts as the monsoon's tail end and finishes in full sunshine. Ang Thong reopens mid-month, and from around December 15-20, prices jump. Heads-up: many resorts add a compulsory Christmas or New Year's Eve gala dinner, often 2,500 to 8,000 baht per adult. The payoff is New Year's Eve fireworks over the Gulf.
So, Which Month Is Yours?
That's Koh Samui weather in a nutshell. For near-guaranteed sunshine, aim for February through April. For deals and quiet beaches, May, June, and September are my sleeper picks. My full guide to the best time to visit Koh Samui breaks it down by travel style. There's no bad month here, just different flavors of paradise.
Once you've picked your month, my 7-day Koh Samui itinerary shows you how to fill the week.
FAQ
What is the hottest month in Koh Samui?
April and May tie for hottest, with highs around 90-92°F. April feels more intense thanks to clearer skies, while May adds cooling afternoon storms.
What is the wettest month in Koh Samui?
November, averaging roughly 12-18 inches of rain, often in multi-day storms. Late October and early December can be wet too.
Is Koh Samui's rainy season the same as Phuket's?
Nope. Phuket's wet season runs roughly May to October, while Samui's heaviest rain lands from late October to mid-December.
How warm is the sea in Koh Samui?
Warm year-round, from about 82°F in the cooler months to roughly 86°F from April through June.
Do Koh Samui's waterfalls dry up?
They can shrink to a trickle from February to April. They look their best from September to December, though trails get slippery after heavy rain, so wear shoes with real grip.
Got more questions? My Koh Samui Weather & Seasons FAQ tackles eight more.
