Gulf of Thailand Weather

Two coasts, two monsoons

Thailand's beach weather confuses people for one simple reason: the country's two coastlines have nearly opposite rainy seasons. The Andaman side — Phuket, Krabi, Koh Lanta — is hit by the south-west monsoon from May to October, when its seas turn rough and its skies grey. Many travellers read 'rainy season in Thailand' and assume the whole country is under water.

Clear-day beach weather at Ban Krut on the Gulf coast

The Gulf coast runs the other way. Sheltered from the south-west monsoon, Ban Krut, Koh Samui, Koh Tao and Koh Phangan stay largely dry through the European summer, with only brief storms. Their rain arrives late, with the north-east monsoon: October to December is the Gulf's wet window, and November–December is when the seas around the islands turn genuinely rough. The practical rule: November to April, lean Andaman or the dry-season Gulf; May to September, the Gulf is clearly the better coast.

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At a glance

Gulf coast (Ban Krut, Samui, Tao, Phangan): dry December–April, largely dry June–August
Gulf's wettest months: October to December
Andaman coast (Phuket, Krabi): wet May to October
Gulf seas around Samui, Tao and Phangan turn rough November–December

Good to know

Booking for the European summer? Default to the Gulf coast — it is the right side of the country in July and August.
Travelling October–December, build flexibility into island plans: ferries and dive boats answer to the sea, not your schedule.
Rain on the Gulf tends to come in bursts — wet-season mornings are often the driest part of the day.
The mainland Gulf coast (Ban Krut, Hua Hin) suffers less from rough seas than the islands — a good wet-season compromise.

The Gulf's year in three acts

Act one, December to April: the classic dry season. After the rains fade in December, the whole Gulf coast settles into sunshine, calm seas and breezes — the postcard months, and the busiest. March and April turn hot, often above 33°C, before the year's first thunderstorms mark the change.

Act two, May to September: the Gulf's quiet triumph. While the Andaman gets its daily soakings, the Gulf stays mostly dry — hot days, green landscapes, and short, dramatic evening storms that clear quickly. June through August in particular is far drier here than most visitors expect, which is why the Gulf islands are the smart choice for summer-holiday travellers.

Calm dry-season sea on a Koh Samui beach

October to December: when the Gulf takes its turn

Act three is the reckoning. From October the north-east monsoon pushes rain onto the Gulf coast, and October to December is its wettest stretch — sometimes gentle grey days, sometimes proper multi-day downpours. On the islands, November and December add rough seas: ferries can be bumpy or cancelled, dive boats stay in, and beaches lose their sparkle.

It is not a write-off — rain often falls in bursts with bright gaps, prices dip and the crowds thin — but it is the one window when the Andaman coast is the objectively better beach bet. If your dates are fixed in November, consider Phuket or Krabi; if they are fixed in July, do the opposite and come to the Gulf.

Mist over Cheow Lan lake near Surat Thani in the wet season

Month by month

January	Dry and breezy across the Gulf — excellent everywhere
February	Dry, sunny, calm seas — peak conditions
March	Hot and dry; visibility at its best around the islands
April	Hottest month, still dry — Songkran festivities
May	Hot with first evening storms; still a good bet
June	Largely dry and quiet — underrated month
July	Warm, mostly dry, short showers — good Gulf weather
August	Warm with brief storms; far drier than the Andaman
September	More showers creeping in, but plenty of sun
October	The rains arrive — wettest window begins
November	Wet, and island seas turn rough — the Gulf's low point
December	Rain easing through the month; dry season returns late-month

Frequently asked questions

When is the rainy season on the Gulf coast?

October to December. Unlike the Andaman side, the Gulf stays largely dry from December through April and again through most of June to August.

Is Koh Samui dry when Phuket is wet?

Broadly yes. Phuket's wet season runs May to October; Samui and its neighbours stay mostly dry then, with their own rains arriving from October.

Which coast should I choose for July and August?

The Gulf, clearly — Ban Krut, Samui, Tao and Phangan are largely dry then, while the Andaman is in the thick of its monsoon.

Can I still visit the Gulf islands in November?

You can, but manage expectations: it is the wettest, roughest window, and ferries and dive trips can be disrupted. For guaranteed beach weather that month, the Andaman side is safer.

The Gulf coast's upside-down monsoon

Two coasts, two monsoons

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