When to visit

Is Koh Samui or Phuket better in August?

Updated 2 June 2026

Short answer

Koh Samui is dramatically better than Phuket in August — it isn't close. Samui sits on the opposite (Gulf) monsoon calendar and gets around 110mm of rain in August across nine days, with peak sea conditions and excellent diving. Phuket gets around 360mm across 23 days, with red-flag beach warnings, closed dive operators, and the worst price-to-weather ratio of the year because European school holidays keep rates near-peak.

This is the easiest comparison on the Thai calendar — and somehow the one most travellers get wrong. In August, Koh Samui is dramatically better than Phuket. Same country, opposite coasts, opposite monsoons. Phuket is at its wettest and most expensive simultaneously; Samui is at its driest, sunniest, and most reliable.

Here's the side-by-side.

Rainfall and weather

	Phuket (August)	Koh Samui (August)
Monthly rainfall	~360mm	~110mm
Rainy days	~23	~9
Average temperature	28°C	29°C
Sea temperature	28°C	30°C
Dominant weather	Wet, rough, stormy	Hot, bright, calm

Samui isn't dry in any objective sense — but compared to its sister island on the opposite coast, it might as well be. The Gulf monsoon doesn't really arrive until October–December, which is the inverse of the Andaman.

Sea, swimming, and diving

Phuket in August: Andaman Sea is rough, visibility drops to 5–10m, the Similan Islands are officially closed (mid-May to mid-October), and most west-coast beaches fly red flags routinely. Rip currents kill swimmers every season — this isn't an exaggeration, it's a published statistic. Dive operators are mostly closed or running reduced schedules.

Samui (and Koh Tao) in August: Calm seas, sea temperature 30°C, dive visibility 25–30 metres on Koh Tao — this is genuinely peak conditions. Angthong Marine Park day trips run every day. Live-aboards are operational.

If your trip involves any swimming, snorkelling, or diving, this difference alone settles the question.

Prices

Here's the genuinely surprising part: Phuket is more expensive than Samui in August despite being objectively worse. European school holidays push Phuket hotel rates to near-peak levels, even as the weather is at its worst. Samui sees a smaller bump because it's a less well-known European-family destination — so you pay less and get better weather.

This makes August the most lopsided price-to-experience trade in the Thai calendar. You can pay more to be wetter, or you can pay less to be drier. Most people don't realise the choice exists.

When Phuket still makes sense in August

A few legitimate reasons to pick Phuket anyway:

You're already in the region and flights to Samui add hassle (Samui's airport is small and routes are limited)
You want Old Town, food tours, spas, and shopping rather than beach days — Phuket Old Town works in any weather
You're not going for the beach at all and just want a base for indoor activities at a discount-from-peak rate
You have a non-refundable booking from before you knew this

If any of those apply, see our is it okay to go to Phuket in August breakdown for what works on Phuket specifically in monsoon season.

When Samui is the obvious call

Almost everyone else. Beach trip, snorkel trip, dive trip, anniversary, honeymoon, family beach holiday — Samui in August delivers. The catch is logistics: Samui's airport (USM) is small and operated by a single carrier, so flights are pricier than Phuket. Many travellers fly into Surat Thani (URT) and take the ferry — cheaper, slightly longer.

For the full August picture and a suggested itinerary, see our Thailand in August guide.