Andaman Sea
Snorkeling in Thailand: the coast matters, not the month
Translated from the German original.
Now in October
Southwest monsoon — the Andaman side is out
- Water
- 28–30 °C
- Visibility
- much worse, the water turns murky
- To see
- hardly predictable on the Andaman side; in the Gulf of Thailand it's high season now
From May, the southwest monsoon brings high seas, current and murky water to the west coast. The Similans close. If you want to snorkel in these months, go to the east coast — Koh Samui, Koh Tao, Koh Phangan.
Source: Southwest monsoon May–October with high seas, current and murkiness on the Andaman side; high season in the Gulf of Thailand May–September: All4Diving Phuket, Sunrise Divers, The Colours of Thailand
The year at a glance
| Months | Season | Water | Visibility | To see |
|---|---|---|---|---|
| November–April | Andaman Sea — high season | 29–30 °C, up to 32 °C in April | 20–30 m at the reef, up to 40 m at some spots in the Similans | Reef at full strength; the Similan Islands are only open in these months |
| May–October | Southwest monsoon — the Andaman side is out | 28–30 °C | much worse, the water turns murky | hardly predictable on the Andaman side; in the Gulf of Thailand it's high season now |
The values come from my logbook and from named expert sources — each row gives its origin in detail above. Nothing here is estimated.
For Thailand there’s a rule that isn’t in any climate table: The coast decides, not the month.
Andaman Sea or Gulf of Thailand: which coast when?
Thailand’s south lies between two seas. On the left the Andaman Sea with Phuket, Khao Lak, Krabi and the Similan Islands. On the right the Gulf of Thailand with Koh Samui, Koh Tao and Koh Phangan. At the narrowest point, less than fifty kilometers lie between the two — and yet they have their good season in completely different months.
- Andaman Sea: November to April. Dry, calm sea, clear water.
- Gulf of Thailand: May to September. Exactly when the west coast is out.
Anyone who flies to Koh Samui in January hasn’t made the worse choice — they’ve mixed up the coast. And anyone who flies to Phuket in July finds waves and murky water there, while on the other side of the peninsula it’s dead calm.
When are the Similan Islands open?
The Similan Islands are the best-known snorkeling and diving spot on the Andaman side. They are closed from May to October — not because of the weather alone, but because the national park is closed during this time. If you want to see them, you have a window from November to April, and not a day more.
Where I was
I’ve been to Thailand several times, always between December and February — right in the middle of the Andaman high season.
There’s no detailed report from there here yet. What this page says about the conditions comes from specialist sources; they are named in the box above.