Diving in Thailand in May: Gulf vs Andaman Guide

Featured image: Amada44, CC BY-SA 3.0, via Wikimedia Commons.

Is May a Good Month to Dive Thailand?

Yes, if you pick the right coast. Gulf dive operators run steadily in May, and the Gulf's usual dive season runs from May to September. The Andaman Sea sits at the other end of its cycle. Sources disagree on whether its season ends in April or stretches into May, so May is the edge month on that side. Frame the Andaman as variable, not closed and not open. Our parent guide to the Best Time to Dive Thailand: Month-by-Month Guide shows how May fits into the full year. The table below sorts the options by risk.

Gulf of Thailand in May: Koh Tao, Samui and Phangan

Koh Tao is the main training hub, with shallow bays and easy local sites for beginners. Koh Samui suits travelers who want a wider holiday with diving added. Koh Phangan sits between the two and is the closest base to the area's marquee offshore site. Sail Rock is that site, a granite pinnacle that rises about 8 m (26 ft) above the surface. Its maximum depth is about 40 m (130 ft). A vertical swim-through called the Chimney opens at roughly 5 m (16 ft). Depth and entry details vary by source, so ask your operator which route they use.

Boat time shapes the day. Sail Rock is typically about one hour from Phangan and about 1.5 hours from Koh Tao or Samui. Chumphon Pinnacle and Southwest Pinnacle are the other offshore names to ask about from Koh Tao. Both are known for schooling fish. Offshore pinnacles usually need more experience than the bays, so check certification and depth limits before you book.

Andaman Sea in May: What Is Variable

Some operators on the Andaman side still run in early May, and others have already wound down. Weather decides it week by week. Sites reached by day trip are the realistic targets. Hin Daeng and Hin Muang are reached from Koh Phi Phi or Koh Lanta, typically a 1.5 to 2 hour boat ride. From Phuket, expect a full-day trip. Long crossings are the first to be cancelled when seas build.

Liveaboards to the Similans, Surin Islands and Richelieu Rock are the most seasonal option. Marine park access follows national park notices, and published park seasons run to about mid-May. Read the closure notices from the Department of National Parks before you pay a deposit.

If you are traveling at the front of the month, the April diving guide shows the Andaman at its fading best. Later dates lean toward the Gulf, as in the June diving guide.

• Ask which sites are actually running that week.
• Book with a free-change or weather clause where offered.
• Keep one Gulf day or a spare day in the plan as a fallback.

Marine Life in May: Whale Sharks, Mantas and Reef Life

May sits at the tail of the whale shark window in most sources. Estimates range from February to May on one side and March to June on another. Sail Rock, Chumphon Pinnacle and Richelieu Rock are the names that come up. Treat a sighting as possible, never guaranteed. Manta ray season is reported to run from mid-October to about mid-May, so May is the last stretch there too.

Reliable May dives are about reef life and schooling fish. Barracuda and trevally gather around the Gulf pinnacles. Sail Rock also has longfin batfish and giant groupers. Koh Tao's shallower sites reward macro-minded divers. Water stays warm, typically 27°C to 30°C (81°F to 86°F). For a site-by-month comparison, see our Thailand Water Temperature by Month and Sea: What to Wear guide.

If whale sharks are your main goal, March diving is a stronger bet than May.

Gulf or Andaman? Choose by Diver Type

Match the coast to your dates and tolerance for change. Fixed dates and a beginner course point to Koh Tao. A big-animal hunter with flexible dates can try the Andaman with a Gulf backup. A mixed family trip fits Samui best, since non-divers have plenty to do on land.

• Sample Gulf structure (4 to 5 days): arrival buffer day, 2 to 3 dive days, one weather float day.
• Sample Andaman structure (3 to 5 days): arrival buffer day, 1 to 2 day trips, one spare day for cancellations.
• If Andaman trips cancel, the Gulf is the alternative. Transfer time is unverified, so ask your operator.

Getting There and Getting Between Dive Sites

Bangkok Suvarnabhumi (BKK) is the main gateway. Domestic flights to Koh Samui take about 1h15, according to PADI. Phuket and Krabi flights take about 1h25. Samui is your launch point for Phangan and Koh Tao. Phuket and Krabi serve the Andaman.

That split should shape your coast choice. Landing in Phuket makes the Andaman the easy default, but May weather may push you east. Koh Tao and Phangan need a ferry or transfer on top of the flight. No timetables are quoted here because schedules change. Build a first-day buffer so a late flight, a ferry and a boat chain cannot swallow your first dive. Sleep one night before an early boat if you can.

Costs, Booking and Cancellation Trade-Offs

No May price figures are published here. Prices vary by operator, so request current quotes from each shop. Courses usually cost less per dive than liveaboards, and fun dives sit in between. Liveaboards cost the most and carry the biggest cancellation exposure. May is shoulder or low season on the Andaman, which can mean fewer crowds and softer rates. Ask what happens if weather cancels a trip. Look for refund or rebooking terms in writing, not just a verbal promise.

Safety, Currents and Gear Notes for May

Currents can be strong at open-ocean pinnacles, including Koh Tachai, Richelieu Rock and Elephant Head Rock. Pack your own surface marker buoy (SMB) and know how to deploy it. Boat traffic near ascents has caused accidents in recent years. Check certification and depth requirements for Sail Rock and the pinnacles before you commit. Take travel insurance that covers diving. Ask the operator about the day's forecast, the current, and which sites are running that week.

Mistakes to Avoid in May

A few errors cause most of the disappointment on May trips. Avoid these.

• Booking a fixed Similan liveaboard without a weather clause.
• Assuming Andaman visibility matches peak-season claims in guidebooks.
• Ignoring ferry timing to Koh Tao or Phangan on arrival day.
• Chasing whale sharks as if a sighting were guaranteed.
• Skipping the operator's forecast briefing the evening before.

Next Steps

Pick your coast first, then your base, then your backup. For September comparisons, the September diving guide covers Gulf conditions later in the season. Return to the full month-by-month dive guide if your dates are still open.