Thailand spearfishing season: when is visibility actually best?

Thai tourism brochures will tell you the weather is “year-round good.” For spearfishing, that is not true. The season matters enormously, and the Gulf and Andaman coasts are on almost opposite monsoon cycles. Book the wrong week and you lose the trip to murky water and afternoon squalls. Book the right week and you see fish from 15 m away.

I have spent every season of the last decade in Thai water. Here is the calendar that actually works — the one I use to plan my own hunting, the charters I run, and the advice I give customers who message before ordering a speargun.

The short version

• Andaman coast (Phuket, Krabi, Similans region): best November-April. Closed by monsoon May-October.
• Gulf of Thailand (Samui, Chumphon, Hua Hin): best November-April. Monsoon hits May-October with squalls but the Gulf closes harder in October-November with the north-east monsoon pushing a wet reversal.
• Peak month for Thailand as a whole: February. Clean water both coasts, minimal wind, maximum fish activity.
• Worst months to plan a trip: June-September on the Andaman, October-November on the Gulf.

Why Thailand has two different seasons

Thailand sits on two coastlines with separate monsoon patterns. The south-west monsoon blows from April/May to October and hammers the Andaman with rain and swell. The north-east monsoon blows December to February and stirs up the upper Gulf but leaves the Andaman glassy. In between, there are transition months that are often the quietest, most productive windows of all.

For spearfishing specifically, you care about three things: visibility, wind, and fish aggression. Let’s break them down by region.

Andaman coast — Phuket, Krabi, Trang, Ranong

The Andaman at its best is postcard material. 15-25 m visibility, glassy mornings, pelagics holding on offshore pinnacles. At its worst it is unfishable — 1-3 m visibility with vertical rain and 1.5 m swells.

Month	Visibility	Sea	Fish activity	Rating
November	8-15 m	Calming after monsoon	Building	★★★★
December	15-25 m	Calm	Prime reef + pelagic	★★★★★
January	20-25 m	Flat	Prime	★★★★★
February	20-25 m	Flat	Prime	★★★★★
March	15-20 m	Calm, warming	Prime	★★★★
April	10-15 m	Calm, warmer	Still good	★★★★
May	5-10 m	Monsoon arrives	Dropping	★★
June-Sep	2-6 m	Big swells, rain	Dormant	Skip
October	5-10 m	Transition, unpredictable	Low	★

Similan and Surin parks close to tourism from mid-May to mid-October regardless of whether you were planning to go there (and you weren’t, because they are marine parks — full story in our Phuket and Similans guide).

Gulf of Thailand — Samui, Koh Tao, Chumphon, Hua Hin

The Gulf is a different beast. It never reaches Andaman-level clarity, but it also rarely becomes completely unfishable. The calm windows are longer but the ceiling is lower.

Month	Visibility	Sea	Fish activity	Rating
December	8-12 m	Calm most days	Prime	★★★★★
January	10-15 m	Very calm	Prime	★★★★★
February	10-15 m	Very calm	Prime	★★★★★
March	8-12 m	Calm	Good	★★★★
April	5-10 m	Warmer, calm	Good	★★★★
May	3-6 m	Rain, occasional squalls	Mid	★★
June-Sep	2-5 m	Monsoon, choppy afternoons	Low	★
October	3-5 m	North-east monsoon arrives, stirred silt	Low	★
November	5-8 m	Settling	Building	★★★

The Gulf’s real enemy is the autumn reversal. October and November on Koh Samui can be worse than July — the north-east monsoon coming over the peninsula pushes murky water from the north and the water column gets violently mixed. Do not book a Samui trip for October.

Fish activity by season

Visibility tells you if you can see fish. Activity tells you if there are any to see. They are not the same thing.

Dry season (Nov-Apr)

• Reef fish are most active mid-morning (9-11 a.m.) and late afternoon (3-5 p.m.).
• Pelagic movement on outer reefs peaks around February and March on the Andaman.
• GT and cobia push closer to shore on incoming tides in still conditions.

Shoulder seasons (Apr-May, Oct-Nov)

• Plankton blooms reduce visibility but bring baitfish, which brings predators. Counter-intuitively, some of the best pelagic days happen in murky water.
• Fish are less wary because diving pressure is lower.

Monsoon (Jun-Sep on Andaman, Oct-Nov on Gulf)

• Not recommended. Safety risk from squalls outweighs any marginal fishing benefit.
• Use this time for dry training. The breath-hold trainer CO2 tables are how I stay sharp between seasons.

Planning your trip — by goal

”I want to get my first fish and learn”

Aim for January or February on the Gulf. Samui-based out of Lamai works well — you can combine a 3-day Apnea Total Level 1 course with 2-3 hunting days. Calm water, approachable reef fish, no pelagic overwhelm.

”I want pelagics and blue water”

February-March on the Andaman, specifically Phuket-based charter trips to offshore reefs around Racha or Raya Noi (outside park boundaries). You need your Apnea Total Level 2 certification first — open-water pelagic hunting past 20 m requires real training.

”I live in Bangkok and just want weekends”

December-February on the mainland coast around Hua Hin or upper Chumphon. 3-hour drive, legal coastline, no boat needed.

”I’m visiting once, pick the dates”

Second week of February. Highest-probability clear water both coasts. Book that, nothing else.

What about multi-week forecasts?

Mid-term forecasting beyond 5 days is unreliable for Thai coastal conditions. Planning a trip 3 months out, just stick to the season windows above. Within a few weeks of your trip, check the live ocean conditions widget we embed from Freediving Koh Samui — it shows wind, tide, and visibility estimates for popular Thai dive sites.

Note: the widget shows scuba sites, most of which are inside marine parks where spearfishing is banned. Use it for condition context, not for picking your hunt location. For the hunt location, ask a local.

The honest answer

Thailand has a four-month clear-water window and an eight-month everything-else window. If you want consistency, plan December through March. If you want a trip to remember, pick February. If you want to keep your season going year-round, learn to love dry apnea training and Gulf murk days.

Got a specific trip to plan? Message me on WhatsApp with your dates and coast preference — I’ll give you the real call, not the brochure version.