Here is the one thing every mover needs to understand about Samui's weather: it is the opposite of Phuket. Because Samui sits in the Gulf of Thailand, its monsoon runs on a different calendar — it is dry and glorious when the Andaman coast is wet, and wettest in October and November when Phuket is in peak season. Get the timing right and Samui's climate is a joy. Get it wrong and you arrive into the rain.
Thailand's two coasts face opposite seas and opposite weather systems. The Andaman coast — Phuket, Krabi, Phi Phi — is hit by the southwest monsoon, which brings its rain roughly May to October. The Gulf coast — Samui, Phangan, Tao — sits on the other side of the peninsula and runs on a different rhythm, with its wet season landing later, in the autumn.
The practical upshot is the headline of this whole page: Samui is good when Phuket is wet, and worst when Phuket is at its peak. When the Andaman is being rained on from May to October, Samui is relatively dry and pleasant. When Phuket is bone-dry and packed from November to April, Samui has just been through its wettest window. If you are choosing between the two islands, or timing a move, this single fact matters more than any average temperature.
Roughly: Phuket's best is Nov–Apr; Samui's best is Dec–Mar but it also stays decent through the Andaman wet season (May–Oct). Samui's worst stretch — October to December — is exactly when Phuket is hitting peak season. They are mirror images. Choosing a Gulf island for a December beach holiday without knowing this is how people end up disappointed.
A realistic month-by-month guide. “Rain” on Samui usually means intense bursts, not all-day grey — more on that below.
| Month | What to expect | Rating |
|---|---|---|
| December | The wet season is easing but the year can still end damp; improving toward month's end. | Good, drying |
| January | Cooler, drier, fresh sea breezes — one of the loveliest months. | Excellent |
| February | The driest month of the year. Sunny, comfortable, low humidity. | Best |
| March | Dry and warming up — the tail of the prime window. | Excellent |
| April | Hot, building humidity; Songkran festival. Still mostly dry. | Good, hot |
| May | Hotter and more humid, the odd shower — but Samui stays decent while Phuket gets wet. | Good |
| June | Hot and humid, ~29°C, short sharp showers; pleasant between bursts. | Decent |
| July | Similar — warm, humid, brief downpours, plenty of sun. | Decent |
| August | Hot and humid with quick showers; a good Gulf-season window. | Decent |
| September | Rain increasing as the wet season approaches; still sunny spells. | Mixed |
| October | Wet season begins in earnest — rain around ~295mm. | Wet |
| November | The wettest month — around ~445mm. Heaviest rain, rough seas, ferry disruption. | Wettest |
Do not picture days of unbroken drizzle. On Samui, even in the wet months, rain typically falls in intense bursts of 20 to 60 minutes — a heavy tropical downpour, then it clears and the sun returns. You plan around the bursts rather than losing whole days. The hot season (roughly June to August) is genuinely hot and humid at around 29°C, with those quick afternoon showers offering brief relief. Outside the wettest weeks, you get a lot of usable sunshine year-round.
The exception is the heart of the wet season — October and November — when the rain is heavier and more persistent and the sea turns rough. That is the stretch to avoid for a first impression, a beach-dependent visit, or a move where you need to be out and about settling in.
The climate has real, practical implications when you are relocating rather than holidaying:
Samui's climate is a genuine asset — if you understand it is a Gulf island. Aim for December to March for the best of it, know that October and November are the wet, rough-sea low point, and remember the whole thing is the mirror image of Phuket. Time your move with that in mind and the weather works for you, not against you.
December to March, with February the driest and most pleasant month — cool breezes, low humidity and plenty of sun. January and March are also excellent. For a move, arriving in this dry window makes settling in, viewing rentals and learning the roads far easier than during the October–November rains.
Mainly October to December, peaking in November, which is the wettest month at around 445mm, with October around 295mm. This is the opposite of Phuket's wet season. Even then, rain on Samui usually falls in intense 20–60 minute bursts rather than all day, but the sea gets rough and ferries can be disrupted.
Because they sit on opposite coasts. Phuket faces the Andaman Sea and gets the southwest monsoon roughly May to October. Samui sits in the Gulf of Thailand on the other side of the peninsula, so its wet season comes later, in autumn. The result is that Samui is relatively dry when Phuket is wet, and wettest in October–November when Phuket is at its peak.
It depends on the month. Through the Andaman wet season (May–October) Samui actually stays fairly good, with hot, humid weather and short sharp showers. The genuinely wet stretch is October to December, peaking in November — that is the time to avoid for a beach-dependent visit, with heavier rain, rough seas and possible ferry disruption.
The hot season, roughly June to August, runs around 29°C and is humid, with brief afternoon showers offering some relief. April is hot too. The cooler, fresher months are December to March. Expect to use air conditioning heavily in the hot, humid months, which makes electricity the main swing cost in a Samui budget.
Yes, in the wettest weeks. During October and November, rough seas can delay or cancel ferries, which matters because the island depends on boats and planes for both people and goods. If you are moving around then, build slack into your dates and deliveries, and check operator updates. Flights are more weather-resilient than ferries but not immune.