With two separate coasts and two dive seasons, Thailand is one of the few countries where you can dive almost every month of the year—if you know where to go. Thailand diving locations range from beginner-friendly reefs to world-class deep-sea pinnacles, but each has its ideal time of year

Instead of guessing, this guide shows you the best places to dive in Thailand based on season. You’ll learn which months are best for exploring the Andaman Sea, when to switch to the Gulf of Thailand, and how to plan a trip that avoids the rainy season blues. Get your fins ready—it’s time to match your calendar with the current!

Thailand’s Two Coasts, Two Dive Seasons

Thailand has two main coastlines—the Andaman Sea to the west and the Gulf of Thailand to the east. Each coast offers unique diving experiences, but their dive seasons don’t align. Knowing when and where to go is key to getting the best underwater visibility and safest conditions.

The Andaman Sea is best for diving from November to April, when the weather is dry and the sea is calm. The Gulf of Thailand, on the other hand, has its peak season from May to September. These alternating dive windows mean you can plan a diving trip almost any time of year, as long as you choose the right coast.

Andaman Sea – Best Diving Spots and Ideal Months

The Andaman Sea is home to some of the top Thailand diving locations. The west coast’s dry season (Nov–Apr) brings crystal-clear waters and good marine visibility, making it ideal for underwater exploration.

1. Similan Islands

A national park known for manta rays and whale sharks. Dive sites like Elephant Head Rock and Christmas Point are well-known for strong currents and dramatic landscapes. Best visited between November and May.

2. Richelieu Rock

Often ranked among the best dive sites in Thailand, this pinnacle in the open sea offers sightings of large pelagics and macro life. It’s only open during the park season (mid-October to mid-May), so timing matters.

3. Koh Lanta (Hin Daeng & Hin Muang)

These sites are famous for deep walls, purple soft coral, and the chance to spot manta rays. The dive conditions are best between December and April.

4. Phuket & Phi Phi Islands

Accessible dive sites with a mix of reefs and wrecks. Local day trips are available year-round, but peak season brings clearer water and fewer cancellations.

Gulf of Thailand – Dive Sites and When to Visit

When the monsoon hits the Andaman coast, it’s time to switch sides. The Gulf of Thailand shines from May to September, offering calm seas and good diving conditions.

1. Koh Tao

One of the most popular Thailand diving locations for beginners and training courses. Sites like Chumphon Pinnacle and Sail Rock offer a mix of coral gardens, barracuda schools, and occasional whale sharks. Best diving is from June to September.

2. Koh Samui & Koh Phangan

While more known for beaches and parties, these islands also offer decent dive trips. You can access deeper Gulf sites like Sail Rock from here. Water visibility improves during the Gulf’s dry season.

3. Koh Chang

Located in eastern Thailand, this quieter island offers wreck dives and coral reefs suited for intermediate divers. The dive season here peaks around April to October, avoiding the heaviest rains.

Which Side is Right for You?

Choosing between the Andaman Sea and the Gulf of Thailand depends on your travel dates, skill level, and what kind of diving you’re after.

If you’re planning a trip from November to April, the Andaman coast gives you access to more advanced dive sites, better visibility, and a chance to see large marine life like manta rays and whale sharks. It’s great for experienced divers and those looking for multi-day liveaboards.

If you’re traveling between May and September, head to the Gulf of Thailand. Koh Tao is ideal for beginners, offering cheaper courses and easy shore access. The sea is generally calmer, which is better for first-timers or family travelers.

Your choice also depends on location. If you’re based in Bangkok, the Gulf is easier to reach. If you’re exploring the south or arriving via Phuket or Krabi, then the Andaman coast is more convenient.

Dive Calendar for Thailand

Here’s a quick seasonal guide to help you choose Thailand diving locations based on when you plan to travel:

Month	Best Coast	Notable Dive Spots
January	Andaman Sea	Similan Islands, Richelieu Rock, Koh Lanta
February	Andaman Sea	Phi Phi, Hin Daeng, Surin Islands
March	Andaman Sea	Liveaboards to remote Andaman sites
April	Both	Transition month, good on both coasts
May	Gulf of Thailand	Koh Tao, Koh Samui, Koh Chang starts
June	Gulf of Thailand	Chumphon Pinnacle, Sail Rock
July	Gulf of Thailand	Ideal for dive courses in Koh Tao
August	Gulf of Thailand	Peak season continues
September	Gulf of Thailand	Great for calm water diving
October	Transition	Andaman Sea reopens mid-month
November	Andaman Sea	Similan liveaboards start again
December	Andaman Sea	Excellent visibility across the west coast

This Thailand diving locations calendar isn’t just about where to go—it can also help shape your full travel plan. Want to combine diving with island hopping, jungle trekking, or beach downtime? Use the calendar to balance high-season dive conditions with lower tourist traffic. For example, March is a great time for Andaman liveaboards without the holiday crowds, while June offers warm Gulf waters and more peaceful beaches before the European summer rush.

Many travelers also use this calendar to plan multi-stop routes across Thailand. For instance, you might begin in Chiang Mai for cultural exploration in early April, then head south as the Gulf dive season kicks in. Or start your trip diving in the Similan Islands in November and transition east as seasons change. With this kind of seasonal awareness, Thailand diving locations don’t just offer great dives—they can anchor your entire journey.

Thailand diving locations span two coastlines, two seasons, and countless underwater experiences. By aligning your dive trip with the weather and regional dive windows, you’ll get clearer water, safer conditions, and a more enjoyable time in the sea.

A little planning goes a long way. Use the seasonal map to guide when to head west or east, and match your dive goals to the time of year. From deep pinnacles to shallow coral reefs, Thailand offers something exciting every month—it’s just a matter of timing.