The Andaman at Its Finest
December is the month that confirms everything the Andaman promised when you booked your ticket. The northeast monsoon is sitting squarely over the region now, the sky most mornings a faultless blue-white dome, the sea out to the northern archipelagos a moving sheet of deep indigo. Liveaboard departures are full, day charters are running hard, and the fish — led by an accelerating sailfish population — are where they should be.
This is the month that anglers plan around. It shows in the marina demographics: alongside the regular Thailand-based fishing crowd you see Italian and German big-game anglers arriving with travel rods and heavy spinning gear, Australian families making the Similan trip a part of the holiday, and serious popping crews from Singapore and Japan who have timed their trip precisely to hit Koh Bon and Koh Tachai at the peak of the GT season. December on the Andaman is a shared understanding among people who know their fishing.
Conditions: Northeast Monsoon in Full Command
By the first week of December, the southwest monsoon is firmly in the past. Northeast winds were light and consistent through the month, averaging perhaps 10–15 knots on settled days and occasionally dropping to almost nothing in the early mornings. Swell at the offshore grounds was predominantly under a metre, with the glassier days producing conditions that made even long runs to the northern reefs comfortable.
Water temperatures dropped slightly compared to November, sitting in the 27–29°C range at the surface and a degree or two cooler beneath the thermocline. This cooling is significant — it is one of the primary signals that triggers sailfish to aggregate in catchable numbers along the current edges and bait-holding structures that characterise the best offshore grounds. Visibility in the water column was excellent throughout, with blue water clarity regularly exceeding 20–25 metres at the cleaner pinnacles.
The combination of lower surface temperatures, high clarity, and reduced swell is exactly the trifecta that defines Andaman peak season. December reliably delivers all three, which is why it books out so far in advance.
Sailfish: The Bite Accelerates
The sailfish action that was building in November shifted into a higher gear through December. Reports from offshore grounds ranging from the Phuket south coast up to the waters northwest of Phang Nga described consistent sail activity, with fish appearing regularly on teasers and responding well to live bait presentations under outriggers.
Koh Rok remained a productive ground, with the offshore current edges holding bait schools that attracted sails throughout the month. Captains working kite-fishing rigs reported that the fish were willing and multiple releases on a single session were achievable on the better days, particularly when the wind allowed a clean kite to be flown over a productive drift.
The better days offshore were producing multiple sail encounters before noon — fish that ate cleanly and fought well in the cooler, clear water. December sails often run harder than the peak-of-season fish.
Further north, the grounds around the Similan island chain were beginning to produce sailfish alongside the marlin bycatch that occasionally appears when bait concentrations are strong. Liveaboard captains who incorporated a trolling run on their northern itineraries were finding the sailfish presence more widespread than in a typical December, with birds working patches of bait far from the known pinnacle marks.
GT Popping: Consistent Action on the Northern Reefs
The popping crowd had an exceptional month. Koh Bon, consistently the standout GT venue in the early and mid season, was producing strong action through December, with fish responding well across all tidal states when surface conditions allowed a clean cast. The reef plateau structure at Koh Bon tends to concentrate GTs in predictable lanes, and crews who understood the topography were setting up on the right ground and connecting regularly.
Koh Tachai added another dimension to the liveaboard popping agenda. The exposed pinnacles there suit heavier poppers and longer casts — the fish tend to be bigger and the strike more violent than at the flatter Koh Bon reef face. Slow-pitch jigging between popping sessions on these structures accounted for dogtooth tuna in solid numbers, with the fish showing well at depth in the clear conditions.
When GT popping at Koh Bon, the western-facing reef edge produces best on the morning incoming tide. Position the boat so poppers can be worked parallel to the drop-off rather than directly across it — the strikes tend to come from fish holding on the edge rather than up in the shallows.
Liveaboards: Peak Season in Full Swing
December is the peak liveaboard month and the boats reflect that reality: full manifests, keen crews, and itineraries planned to maximise productive fishing time. The standard northern circuit — Similan Islands, Koh Bon, Koh Tachai, Richelieu Rock, Surin group — was running reliably through the month, with operators reporting very few weather-related itinerary adjustments.
Richelieu Rock deserves specific mention. This seamount, which sits in the Surin Marine Park and is accessible only on longer liveaboard itineraries, was fishing well through December. The resident GT population was active and the bait aggregations around the pinnacle structure were attracting a broader predator community — including the occasional whale shark encounter that, while not a fishing target, is an extraordinary encounter for any angler willing to set the rod down for ten minutes.
Looking Ahead to January
January is where the sailfish peak truly arrives. The cooling water temperatures that have been building since October reach their seasonal low through the opening weeks of January, and the sailfish aggregation that forms on the Andaman grounds during this period represents the best bill-fishing opportunity in mainland Southeast Asia. Kite fishing, live-bait drifting, and teaser-and-fly presentations all produce at their highest rates through January and February.
For GT crews, January maintains the December standard — the fish do not disappear and the conditions remain excellent. Liveaboard berths for January that have not already been secured are now extremely limited. Day-charter availability remains reasonable for anglers who prefer to stay based ashore.
Plan your January trip with our sailfish season guide and liveaboard operators overview. For GT-specific itinerary planning, see our GT popping Andaman guide.
