The Phuket Diving Calendar: When to Actually Book

Phuket's diving isn't a 365-day proposition — anyone telling you otherwise is selling a boat ticket. The Andaman Sea has two distinct personalities: a glass-clear high season (mid-October through mid-May) and a moody, green-water monsoon (mid-May through mid-October). This calendar is the honest version — month by month — so you can book the trip that actually matches what you want to see.

The Two Seasons at a Glance

High Season (Nov – Apr): 20-40m visibility, flat seas, water 27-30°C, Similan & Surin National Parks open, whale sharks & mantas peak in Feb-Apr. Prices climb. Book 2-3 months ahead.

Low Season (May 16 – Oct 14): Similan Islands closed by law. Phuket local sites (Racha Yai, Racha Noi, Shark Point, Phi Phi) stay open. Visibility 10-20m, occasional storms, hotel rates 40-60% cheaper, and manta sightings at Racha Noi can actually peak.

Month-by-Month Phuket Diving Calendar

Month	Visibility	Water Temp	Conditions	What's Running
January	20-30m	28°C	Peak-season calm, some plankton blooms	Similan & Surin in full swing; mantas at Racha Noi
February	25-30m	28-29°C	The sweet spot — flat & clear	Whale shark season opens at Richelieu Rock
March	25-30m	29°C	Warm, calm, fewer crowds than Feb	Peak whale sharks & mantas — prime liveaboard window
April	20-30m	30°C	Hottest month, occasional afternoon showers	Last chance for Similan; mantas still active at Koh Bon
May (1-15)	15-25m	30°C	Shoulder — first swells appear	Similan & Surin close on May 16
May (16-31) – Oct 14	10-20m	29°C	Monsoon: wind, rain, swells	Phuket local sites only; mantas possible at Racha Noi
June – July	10-20m	29°C	Wet & windy but workable	Shark Point, Anemone Reef, King Cruiser Wreck
August	10-15m	29°C	Wettest month, some trip cancellations	Cheap fills & hotels; best for budget divers
September	10-20m	29°C	Still monsoon — weather improving late month	Local Phuket boats only
October (1-14)	15-20m	29°C	Season turning — variable	Final weeks before Similan reopens
October (15-31)	20-25m	29°C	Similan reopens Oct 15 — few crowds	Shoulder bargain; liveaboards restart
November	25-35m	28°C	Excellent — often the clearest of the year	Everything open; few tourists pre-holiday
December	25-40m	28°C	Best viz of the year; Christmas/NY crowds	Full Similan & Surin; prices peak at holidays

Marine Life Seasonality — When to See What

• Whale sharks: Nov – May, peak Feb – Apr at Richelieu Rock & Koh Tachai.
• Manta rays: Peak Feb – Apr at Koh Bon & Koh Tachai Pinnacle; secondary peak at Racha Noi in Mar – May during plankton blooms.
• Leopard sharks & bamboo sharks: Year-round at Shark Point & Phi Phi.
• Seahorses & ghost pipefish: Year-round macro at Racha Yai.
• Giant morays & turtles: Always in season.

Similan Islands: The Hard Rule

The Similan & Surin National Parks are closed by the Thai government every year from May 16 through October 14. No exceptions, no loopholes. If you want Similan, Koh Bon, Koh Tachai, or Richelieu Rock, you must dive between October 15 and May 15. Liveaboards run roughly November through early May.

Crowds & Prices

December 20 – January 10 and Chinese New Year (late Jan / early Feb) are the most expensive and crowded. February and March are the sweet spot: best marine life, prices easing slightly, and liveaboards still running on normal schedule. October 15 – November and late April are shoulder bargains — same reefs, 20-30% cheaper, half the crowds.

Our Honest Pick

If you only dive Phuket once: first two weeks of March. Visibility is 25-30m, water is warm, whale sharks and mantas are peaking at Koh Bon and Richelieu, holiday crowds have gone home, and liveaboard prices drop off the Christmas peak. If you're on a budget and flexible: late October or late April — shoulder pricing with almost full-season conditions.

Ready to Book?

We run day trips from Phuket year-round and Similan liveaboards from late October to mid-May. Tell us the month you're thinking and we'll tell you honestly whether it's worth the flight. Browse current schedules at siamdive.com.