Best Time to Visit Thailand's Islands: Koh Samui, Phuket & Krabi

I’ve spent a cumulative six weeks spread across Koh Samui, Phuket, and Krabi over the last three years, and the one thing I learned the hard way is that “Thailand season” is a lie. Each island cluster has its own monsoon rhythm, and showing up in the wrong month can mean sideways rain for four days straight. Here’s the real breakdown of when to go—and when to skip—based on actual trips, not generic weather charts.

What’s the weather actually like on Koh Samui vs. Phuket vs. Krabi?

The biggest mistake most guides make is lumping all Thai islands together. They don’t share the same rainy season. Koh Samui sits in the Gulf of Thailand, while Phuket and Krabi face the Andaman Sea. Their monsoon calendars are almost opposite.

On my first trip, I flew into Phuket in early November expecting sunshine. Instead, I got daily downpours that turned Patong’s beach into a brown slurry. Meanwhile, a friend on Koh Samui that same week was posting photos of blue skies from Bang Rak pier.

The Gulf islands (Koh Samui, Koh Phangan) get most of their rain from October to mid-December. The Andaman side (Phuket, Krabi, Phi Phi) gets hammered from May through October. The sweet spot—where both sides are decent—is January through March. That’s the high season everywhere, and you’ll pay for it.

Koh Samui best weather: January to March, then July to September (drier than people think)
Phuket best weather: November to April (December–March is peak)
Krabi best weather: Same as Phuket—November to April, with March being the driest month
Rainy months to avoid: October–November for Koh Samui; May–October for Phuket and Krabi

When should I visit Koh Samui for fewer crowds and lower prices?

If you want to dodge the European winter crowd, aim for late August or September on Koh Samui. Most guides tell you to avoid this period because it’s “rainy season” on the Gulf, but I spent ten days on Samui in September 2023 and got sun seven of them. The rain came in short afternoon bursts—enough to cool things down, not enough to ruin a day.

We stayed at The Library in Chaweng, which was half the price it would have been in January. Chaweng Beach was busy but not shoulder-to-shoulder. Lamai was even quieter. The one downside: a few beachfront restaurants close for renovation during this window, but the food scene in Fisherman’s Village on the north coast stays open and lively.

Low season (May–October): Hotel rates drop 40–60% vs. December peak
Shoulder season (April & November): Decent weather, thinner crowds, moderate prices
High season (December–March): Book everything three months ahead or you’re stuck in a bad room

Is Phuket worth it during the rainy season?

I’ll be honest: I wouldn’t do it again. I tried Phuket in late May once, and the west-coast beaches—Kata and Karon—had red flags up every day. The Andaman Sea gets rough, and the lifeguards mean it. You can still do indoor stuff (cooking classes, the Big Buddha, shopping in Phuket Town), but the whole point of Phuket is the water.

That said, if you’re on a shoestring and only have May–October available, stick to the east side of the island. Cape Panwa and Ao Yon are more sheltered. I had a decent afternoon kayaking out of Ao Yon Beach while the west side was getting pounded.

Best months for Phuket beaches: December, January, February (flat water, clear skies)
Months to skip entirely: June, July, August (consistent rain and big surf)
Hidden gem timing: Early November—still wet, but the crowds haven’t arrived yet and prices are low

What’s the best window for Krabi and the islands around it?

Krabi’s mainland (Ao Nang, Railay) and its offshore islands (Phi Phi, Koh Lanta) share the Andaman monsoon. But Krabi has a microclimate advantage: the limestone karsts block some of the wind, so even in shoulder months you can find pockets of good weather.

I went to Railay Beach in early April, which is technically the tail end of hot season. It was 35°C and humid, but the water was bath-warm and the crowds were thinning out. The walk from Ao Nang to Railay East took ten minutes by longtail, and we had Phra Nang Cave Beach almost to ourselves by 4 p.m.

For Phi Phi, don’t bother going between June and September unless you’re okay with cancelled ferry crossings. I got stuck on Koh Phi Phi Don for an extra night in July 2022 because the waves shut down the pier. The island’s infrastructure isn’t built for that kind of weather.

Prime Krabi window: November to March (perfect for island hopping)
Hot but tolerable: April (fewer tourists, but carry a fan in your room)
Avoid for island trips: June–September (ferry cancellations are common)

Should I book tours in advance or find them on the ground?

I’ve done both, and I lean toward booking ahead in high season and winging it in low season. In December on Koh Samui, the Ang Thong Marine Park day tours sell out two days in advance. I booked through a local shop in Chaweng the night before and still ended up on a cramped speedboat with 30 people.

In low season, you can haggle. I walked down to Lamai Beach in September and found a longtail boat operator willing to take me to Koh Tan for snorkeling at half the posted price because he had no other customers. Just check the weather the morning of—tours will run even if it’s overcast, but they won’t refund if it pours.

Book ahead: Ang Thong Marine Park, Phi Phi day trips, James Bond Island tours
Buy on the spot: Private longtail charters, snorkeling near shore, sunset cruises
Skip entirely in rain: Any open-water snorkeling tour (visibility drops to zero)

Where should I stay based on the season?

Your choice of accommodation matters more than the island itself when the weather turns. On Phuket, a hotel on the west coast in monsoon season is a bad bet. On Koh Samui, a bungalow on the east coast (Chaweng, Lamai) catches the morning sun and avoids the prevailing winds.

I stayed at Sawasdee Village in Kata, Phuket during a rainy October trip, and the pool was unusable because of windblown debris. Meanwhile, a friend at Cape Sienna in Kamala—a more sheltered bay—had a fine time. On Krabi, Centara Grand Beach Resort on Railay West is a good year-round pick because the bay is protected by cliffs.

Koh Samui, dry season: Any beach works, but Choeng Mon is calmest
Koh Samui, rainy season: Stay on the north coast (Bang Rak, Maenam) for less wind
Phuket, any season: Kata Noi or Karon for consistent swimmable water
Krabi, rainy season: Ao Nang has more restaurant options; Railay can feel isolated in bad weather

FAQ

Can I visit all three islands in one trip? Yes, but you’ll lose a full day to transfers. Fly into Phuket, take a ferry to Koh Samui (via Surat Thani or a direct catamaran in high season), then fly from Samui to Krabi. Don’t try it during monsoon—ferries get cancelled. I did it in March and it worked fine, but it’s not a relaxing itinerary.

Which island has the best weather in November? Koh Samui, by a wide margin. November is the start of Samui’s dry season and peak of the Andaman rains. I spent Thanksgiving week on Samui two years ago and had one rainy afternoon. Phuket and Krabi were getting daily storms.

Is it worth going to Railay Beach if it’s raining? Only if you’re staying there. Railay is a pain to leave in bad weather because you need a longtail to get back to Ao Nang, and those stop running if the sea gets rough. If you’re just day-tripping, skip it. I made that mistake once and ended up soaked and stranded for three hours.

Conclusion

Visit Koh Samui in January–March for perfect weather, or August–September for deals and still-decent sun
Skip Phuket entirely June–August unless you’re fine with rain and rough seas
Krabi’s best months are November–March, but April is a solid budget window
Book tours ahead in high season; negotiate in low season
Match your accommodation to the prevailing wind direction for that island’s season