Best Thai Islands to Visit by Month: A Complete Climate Guide

Why Season Matters When Choosing a Thai Island

If you’re planning a trip to an island in Thailand, chances are you’ve already pictured yourself on a beach. Maybe it’s a quiet stretch of white sand, turquoise water lapping at your feet, and a cold drink in hand. Sounds like paradise, right? The thing is, not every Thai island fits that postcard image all year round.  You’re coming expecting sunshine.  But that’s not guaranteed. 

Thailand’s weather is sneaky. While one coast is soaking up the sun, another might be getting absolutely drenched. Some islands are perfect in January but borderline miserable in August. And if you’ve never visited before, it’s easy to assume all the islands share the same weather. (Spoiler: they definitely don’t.)

Most travel blogs gloss over this part.

You’ll read things like ‘the best time to visit Thailand is November to February’ and move on. But Thailand’s more complicated than that. With over a thousand islands scattered across different seas and coastlines, the seasons don’t always follow the script. Pick the wrong island at the wrong time and you could spend your holiday watching rain pour down from your bungalow porch while that snorkeling trip you booked gets canceled. Again.

This guide was made to help you avoid that mess.

Instead of tossing out a generic ‘best islands’ list, I will walk through each month of the year and show you where to go, when to go, and why it matters. Breaking down actual weather data, highlight seasonal pros and cons, and point you toward the islands that truly shine in each part of the year.

Yes, you’ll see the usual big names like Phuket and Koh Samui, but this article is going to dig a little deeper. Islands like Koh Chang or Koh Lipe might not always make the top 10 lists, but in the right season, they’re magic. You’ll find out when they’re at their best and when to steer clear.

So before you book that flight or fall in love with an Instagram reel, stick around. Choosing the right island for the right month isn’t just smart travel planning, it can be the difference between a trip you remember fondly and one you’d rather forget.

Having said all that, it’s worth remembering that many people will also choose to avoid peak months and the most popular islands.  In which case, this guide is also for you.  Use it to avoid everyone else who is looking for guaranteed good weather. There’s a lot of pluses to low season travel. 

Thailand Island Weather: What You Need to Know Before You Book

Here’s something a lot of travelers don’t realize until it’s too late: Thailand doesn’t have one single rainy season. It has several.  They hit different parts of the country at different times. Which means when Phuket is getting pounded by tropical downpours, visitors to Koh Chang may well be soaking up the sunshine. ( And vice-versa )

To make things even trickier, most weather apps aren’t that helpful in Thailand. You’ll often see thunderstorms every day of the week, even if it just rains for 20 minutes at night and the rest of the day is blazing hot. So instead of relying on vague forecasts, it helps to understand the big picture.

Thailand’s islands are spread across three main regions:

• The Andaman Coast (west side)  This includes Phuket, Krabi, Koh Phi Phi, and Koh Lanta.

• The Gulf of Thailand (south-central east)  Think Koh Samui, Koh Phangan, and Koh Tao.

• The Eastern Seaboard Mostly around Koh Chang and nearby smaller islands like Koh Mak and Koh Kood.

Each region follows its own rhythm when it comes to rainfall, sunshine, and sea conditions. If you’re the kind of traveler who’d rather not get caught in a tropical storm or miss your ferry due to rough seas, it’s worth paying attention to the seasonal patterns.

To help you out, I’ve pulled together actual climate data from across the country. The table below compares monthly rainfall and sunshine hours for three popular islands: Koh Chang, Koh Samui, and Phuket to give you a side-by-side look at what kind of weather you can expect throughout the year.  These are based on long-term monthly climate averages, not daily forecasts. from reliable climatological sources.  ( Links are at the end of the article.)

Average Monthly Rainfall for Koh Chang, Koh Samui and Phuket

Rainfall Summary

• Koh Chang has the heaviest rainfall of the three islands, especially during the monsoon. From June to October, it’s consistently soaked, peaking in September with over 660 mm. The dry season (November–February) is very pleasant and much drier, with barely any rain in January and December.  November and March are excellent fringe months to visit.

• Koh Samui follows a different weather pattern, with its rainy season peaking later than the others, mainly in October and November, where rainfall can top 400 mm. It’s surprisingly dry in February and March, making those months ideal for sunshine seekers.  

• Phuket follows a more typical Andaman monsoon cycle, with heavy rains from May to October, peaking in May and September. Rainfall drops off sharply in December through March, making that stretch the most popular window for beach holidays.

Average Hours of Sunshine per Month for Koh Chang, Koh Samui and Phuket

Sunshine Summary

• Koh Chang enjoys the sunniest start and end to the year, with over 250 hours of sunshine in January, February, and December. However, from June to September, it sees the lowest sunshine totals. Dropping to just 70 -120 hours, due to heavy monsoon cloud cover.
• Koh Samui has relatively consistent sunshine throughout the year, with no extreme highs or lows. Even during the wettest months (October – November), it still sees 110 – 120 hours of sun, making it a good choice when other regions are gloomy.
• Phuket shines brightest from December to March, with 240 – 270 hours of sun per month. It dims a bit during the southwest monsoon (May to October), bottoming out at 120 – 150 hours, but still has more sun than Koh Chang in those same months.

Best Islands in Thailand by Month

Choosing the right island at the right time can make all the difference. Some are picture-perfect in high season, while others quietly come alive in the shoulder months, away from the crowds. Here’s what to expect, month by month.

January: Peak Season Perfection

Best for: Koh Lanta, Koh Lipe, Koh Chang
Avoid: Samui (can be wetter than expected)

January is about as good as it gets. The skies are clear, the sea is calm, and everyone’s in holiday mode, from Scandinavian snowbirds escaping winter to backpackers just starting their Southeast Asia circuit. It’s high season on both coasts, but the Andaman side really shines.

Koh Lanta and Koh Lipe are particularly lovely this time of year. Warm but not too hot, with that lazy “we could stay another week” kind of vibe. Koh Chang is also in great shape, with minimal rain and plenty of sun, but not as busy as the southern islands.

Expect: 28–32°C during the day, with light breezes and postcard sunsets almost every night.
Tip: Book accommodation early, especially if you’re traveling mid-month or around New Year. Ferries and flights fill up fast.

February: Sunniest Month of the Year

Best for: Koh Tao, Koh Ngai, Koh Kood
Avoid: Nowhere really. Everything’s great

If you had to pick one month to visit the Thai islands, February would be a strong contender. Rain is rare. The sea’s like glass. And the weather is consistent across the board.

It’s also a fantastic month for diving and snorkeling. Visibility is top-notch, especially around Koh Tao and Koh Ngai. Lesser known islands like Koh Kood and Koh Jum are perfect for unplugging without the high-season madness of Phuket or Phi Phi.

Expect: Dry, breezy days, with temperatures around 30°C.
Tip: Inland Thailand is already heating up, so if you’re choosing between Chiang Mai and the coast, the islands win this round.

March: Dry, Sunny, and Getting Hot

Best for: Koh Phi Phi, Koh Samui, Koh Mak
Avoid: Still nothing major to steer clear of, but expect hazy skies in the Gulf and eastern islands. 

March is when the thermometer starts to climb, but the beaches are still a joy. It’s dry, it’s sunny, and the crowds begin to thin just enough to feel like you’ve got space to breathe.

Koh Samui starts coming into its own now. You’ll get great weather without the big holiday rush. Koh Phi Phi is at its sunniest and least stormy. If you prefer quiet escapes, this is one of the best months to explore under-the-radar spots like Koh Mak before the summer rains creep in.

Expect: Hotter afternoons (up to 34°C), but still manageable with a breeze.
Tip: If you’re combining island time with some northern Thailand trekking, do the north first — it gets hazy and smokey later in March.

April: Hot Season Kicks In

Best for: Koh Samui, Koh Phangan, Koh Chang
Avoid: Inland Thailand (unless you like saunas)

April is the hottest month of the year in Thailand. It’s also the month of Songkran, the Thai New Year, which brings water fights, public holidays, and one of the biggest national celebrations. On the islands, it’s a bit more chilled, though you might still get ambushed with a bucket of water.

If you can handle the heat, this is a great time to be on the coast. The sea is warm, the skies are clear, and most islands are still easily accessible. Koh Samui and Koh Phangan are ideal, and Koh Chang hangs onto its dry spell a little longer before monsoon creeps in.

Expect: 34–36°C most days, high humidity, and warm evenings
Tip: Book accommodation with a pool or decent air-conditioning. You’ll need a way to cool down.

May: The Rains Begin (But It’s Not All Bad)

Best for: Koh Samui, Koh Tao
Avoid: Phuket, Krabi, Koh Chang (rains ramp up fast)

May is a mixed bag. On the Andaman Coast (Phuket, Krabi, Lanta), the southwest monsoon starts to stir. That means more humidity, scattered storms, and rougher seas. But on the Gulf side, things are still fairly calm. Koh Samui and Koh Tao hold onto decent weather and sunshine, making them your best bet if you’re visiting in May.

That said, May isn’t a write-off. Prices drop, crowds thin, and if you don’t mind the occasional downpour . Usually short and sharp in the late afternoon.  So it can still be a good time to travel, even on Koh Chang where any heavy rain is often in overnight thunderstorms.

Expect: High humidity, 30–34°C, and sudden tropical showers
Tip: Be flexible. If it rains one day, treat yourself to a long lunch and a beach massage. The sun usually comes back quickly.

June: Shoulder Season Sweet Spot

Best for: Koh Samui, Koh Tao
Avoid: Koh Lanta, Koh Chang, Phi Phi

June is technically the low season, but that doesn’t mean it’s a bad time to go. In fact, if you’re heading to the Gulf islands, it’s a bit of a secret win. Koh Samui and Koh Tao are still sunny most days, the prices are lower than peak season, and the pace is slower in a good way.

Over on the Andaman side, monsoon is in full swing. Ferries can be inconsistent, and some smaller islands shut down for a couple of months. Koh Chang is often soggy and misty, which has its own kind of charm.  But not ideal if you’re a sunworshipper looking for a beach holiday.

Expect: Warm days with a few afternoon showers, 29–33°C
Tip: Great time to learn to dive on Koh Tao. Visibility is solid, and instructors aren’t overworked.

July: Rain in the West, Sun in the Gulf

Best for: Koh Samui, Koh Phangan
Avoid: Phuket, Koh Lanta, Koh Chang

By July, the southwest monsoon is properly settled on the Andaman Coast, and places like Phuket, Krabi, and Phi Phi are getting regular rain and choppy seas. Some days are clear and sunny, but it’s a gamble. If you’re heading that way for a short holiday, you might end up staring at the sea from a soggy café wondering what could’ve been.

The Gulf islands,  especially Koh Samui and Koh Phangan , are the safer choice. While the skies aren’t always cloudless, there’s a lot more sunshine than rain, and sea conditions are generally much calmer.

Whereas Koh Chang sees rain almost daily and you’ll need to have the weather gods on your side if you’re looking for a few days of uninterrupted sunshine.

Expect: 30–32°C, with occasional downpours that pass quickly
Tip: Flights to Koh Samui are pricier in July due to European holidays. Consider flying to Surat Thani and taking the ferry to save money.

August: Still Good in the Gulf

Best for: Koh Samui, Koh Tao
Avoid: Koh Chang, Phuket, anywhere west coast

August is Thailand’s version of European summer. Meaning there are plenty of tourists, especially families on school holidays. But it’s also smack in the middle of the rainy season on the Andaman side, so unless you’re after quiet, grey-skied beaches, stick to the Gulf.

Koh Samui remains your best bet for mostly dry weather, with sunshine peeking through most days. Koh Tao is still a good option too, particularly for diving. Koh Phangan has some of the clearest beaches in the Gulf and fewer families than Samui.

In the east, Koh Chang and neighbouring islands, are very hit and miss weather-wise.  Flip a coin, take a chance or come expecting the worst but leave pleasantly surprised if it’s drier than expected.

Expect: Mostly sunny mornings, with possible afternoon showers
Tip: This is a good month to explore the inland side of Samui.  Waterfalls are flowing, and the jungle is lush.

September: Wettest Month of the Year (Almost Everywhere)

Best for: Samui (but even here, expect some rain)
Avoid: Koh Chang, Phuket, Koh Phi Phi

September is a tough month to recommend for island hopping. Rainfall is high on both coasts, seas are rough, and many beachfront bungalows are closed for maintenance or just taking a break until the weather clears.

That said, all islands sometime pull off a surprise. You might still get a string of dry days. Just go in with realistic expectations. If you’re planning a beach-heavy trip, maybe hold off until October or switch gears and focus on cultural travel in central or northern Thailand instead.

Expect: 29–31°C, humid, and fairly soggy
Tip: If you’re traveling now, go with flexible bookings. You might want to move around depending on where the weather clears up.

October: A Month of Transition

Best for: Koh Samui, Koh Phangan (early Oct); Koh Lanta, Phuket (late Oct)
Avoid: Koh Chang (still very wet most of the month)

October is the month where everything starts changing but not always at the same time. It’s a bit like flipping a coin with the weather. In the Gulf of Thailand, rains start to increase toward the end of the month. On the Andaman Coast, the rain starts to let up. So depending on your travel dates, your experience could go either way.

Early October: Stick to Koh Samui or Koh Phangan if you want sun and smooth ferry crossings.
Late October: You’ll start to see more blue sky days in Phuket, Koh Lanta, and even Krabi, though storms may still roll through now and then.  On Koh Chang the weather will improve noticeably the later in the month you visit.

Expect: Variable weather, highs around 30°C, rising sunshine hours
Tip: This is a sweet spot for bargain hunters.  Hotels aren’t busy and flight prices are often at their lowest.

November: The West Coast Wakes Up

Best for: Koh Lanta, Koh Phi Phi, Phuket, Koh Lipe
Avoid: Koh Samui (wettest month of the year there)

November marks the official start of dry season on the Andaman Coast, and it’s one of the best times to visit that side of the country. The seas calm down, the rain clears out, and ferry schedules return to normal. Everything starts feeling alive again.  Beach bars reopen, dive shops gear up, and sunset spots fill with happy hour crowds.

Meanwhile, Koh Samui gets hit with its rainiest month. It’s the worst time to be there, with flooding not uncommon. Skip the Gulf this month and head west or over to the east.

Koh Chang’s rainy season ends in early November and it’s often one of the best times to visit. Plenty of sunshine, but without the crowds.

Expect: 28–32°C, low humidity, calm seas
Tip: November is still considered ‘shoulder season’ in many places, so you can find good deals before the December rush.

December: Peak Season Begins Again

Best for: Everywhere on the west coast. Phuket, Koh Lanta, Koh Lipe, Railay.  And great for Koh Chang.
Avoid: Koh Samui (first half of the month still rainy).

By mid-December, Thailand is back in full swing. The Andaman Coast is reliably sunny, the sea is flat and swimmable, and beach towns are buzzing with new arrivals. It’s the start of the high season, and while prices begin to climb, the overall atmosphere is hard to beat.

If you’re looking for postcard-perfect holidays, Koh Lipe is a dreamy choice with powdery sand, clear water, and fewer crowds than Phuket. Koh Lanta is ideal for families or couples looking for a more relaxed vibe. Even Phuket, for all its development, shines in December and you’ll avoid the busiest time of year\.

Koh Samui will still be drying out in the first half of the month, but it starts to stabilize by Christmas. Just don’t expect flawless weather early on.

As for Koh Chang, the weather is usually excellent, although there may be some rain earlier in the month

Expect: 29–31°C, sunny skies, mild evenings
Tip: Book ferries and accommodation early if you’re visiting around the holidays.  Things fill up fast from mid-December onward.

Final Tips for Planning Your Island Escape

You’ve now got a month-by-month breakdown, actual climate data, and a pretty solid sense of when and where to go. But before you head over to the booking sites, here are a few extra tips that can help turn a good trip into a great one:

 1. Always Check the Ferry Schedule First

Even if the island looks perfect on paper, boats don’t always run the way you expect especially in low season. Some smaller islands (like Koh Lipe or Koh Mak) can be harder to reach during monsoon months. Always double-check ferry routes and times before locking in your accommodation.

2. Samui Isn’t the Only Airport

If you’re headed to the Gulf islands, flying into Surat Thani or Nakhon Si Thammarat can save you a lot of money over flying directly to Koh Samui. The ferry ride is a bit longer, but you’ll often save enough baht to cover a few coconut shakes and a beach massage.

3. Don’t Chase the “Best” Island . Pick the Right One for You

Some travelers want quiet beaches and jungle walks. Others want nightlife, diving, or a beach bar with bean bags and live music. Don’t get hung up on the most popular name. Find the island that fits your mood, your budget, and the season.

 4. Rain Isn’t a Dealbreaker (Usually)

A lot of people panic when they see ‘rainy season’, but the reality is often far more forgiving. In many places, it just means heavy is often in the late afternoon or overnight. You’ll still get hours of sun, fewer crowds, and lower prices. Just bring a light rain jacket and roll with it.

5. Trust Local Info More Than Forecast Apps

Weather apps aren’t great at capturing tropical patterns. If you want to know what’s really happening on a specific island, check local Facebook groups or message your hotel or guesthouse. Locals will tell you if the sea is rough, if it’s rained all week, or if it’s been weirdly dry for the season.

To Summarise –  Choose the Month, Then the Island

Planning a trip to Thailand shouldn’t feel like a gamble with the weather if you’re a sunseeker. Once you know how the seasons shift across the country, you can time it just right.  Swap soggy disappointment for sunset swims and jungle hikes.

Thailand’s islands are amazing year-round. You just need to know where the sunshine’s hiding. 

Data Sources:

Rainfall Data Sources:

1. Koh Chang
2. Koh Samui
3. Phuket

Sunshine Hours Data Sources:

1. Koh Chang
   • Estimated based on satellite data + regional modeling
   • Source: Derived from nearby Trat station + climatological interpolation
     (No direct sunshine station on Koh Chang; used modeling based on nearby stations and Weather Atlas)
2. Koh Samui
3. Phuket

Note: Sunshine data is harder to source precisely in Thailand because the TMD doesn’t publish granular solar radiation or sunshine hour data publicly for all stations. The data provided here is an estimate. A combination of satellite-derived climatology, local weather station summaries, and interpolated global datasets (like NASA POWER or NOAA).