May is the month Thailand's fishing calendar resets. The southwest monsoon — the great seasonal engine that drives the country's ecology, agriculture, and marine weather — begins its arrival from the southwest, typically making landfall on the Andaman coast during the first two weeks of May. The Phuket beach resorts hang their half-price banners. The offshore charter boats go up on dry-land cradles. And anglers who know what they're doing quietly pivot to the Gulf, the Bangkok lakes, and the wild freshwater rivers that are beginning their seasonal pulse.
This is a transition month. Not bad for fishing — different for fishing.
The Weather and Water This Month
The southwest monsoon's arrival is not a single dramatic event but a progressive establishment. Pre-monsoon conditions — heavy afternoon squalls, building humidity, occasional strong southwest winds — have been present since late April. By mid-May, the transition is typically complete on the Andaman side, and rain arrives with increasing frequency and intensity.
Bangkok and central Thailand experience May as the first true wet month of the year, though rainfall is still inconsistent. Some years May in Bangkok is mostly hot with scattered storms; other years, the monsoon pulses strongly early and the second half of the month is rainy and overcast. Temperatures remain high — 33–36°C — with high humidity making the heat index feel oppressive. Night temperatures stay warm, offering less relief than the dry season months.
The Gulf of Thailand is much less affected by the southwest monsoon in May. The Gulf's eastern coast — Koh Samui, Koh Phangan, Koh Tao — sits in the lee of the Thai peninsula and doesn't receive the monsoon's full impact until later in the year. May is generally a stable, fishable month on the Gulf.
The Andaman coast — Phuket, Khao Lak, Krabi — receives the monsoon directly. Seas deteriorate through the month, with southwest swells building and offshore conditions becoming unpredictable and often rough. This is not a month for Andaman offshore fishing unless you have very specific local knowledge and flexibility.
The monsoon is a transition, not a shutdown
Most of Thailand's freshwater fishing — and the Gulf — continues right through the wet season. The Andaman offshore circuit is the main casualty. Don't let the words "monsoon season" put you off visiting or fishing in May.
Freshwater Fishing This Month
Bangkok Pay-Lakes — A Quieter Rhythm
May marks a shift in Bangkok's pay-lake scene. Overseas tourist numbers drop as the Andaman's beach tourism slows and the "high season" narrative fades. Venues become less crowded. Pricing at some lakes eases — not dramatically, but noticeably at venues that had been running premium rates through the peak season.
The fishing itself doesn't pause. Bungsamran Lake operates year-round, and its roster of giant Mekong catfish, giant Siamese carp, and arapaima is as active in May as any other month. Warm water temperatures — often 29–31°C in the lakes — keep metabolism high and feeding frequent. The challenge is comfort, not catch rates.
Morning sessions remain the most productive and least punishing time slot. Dawn to 10 a.m. is prime. Overcast, pre-rain days — common in May — actually extend the comfortable fishing window compared to April's relentless sun. When a cloud layer sits over Bangkok and keeps direct sun off the water, afternoon sessions become feasible in a way they weren't in April.
IT Lake Monsters is productive for alligator gar and arapaima in May's warm water. Palm Tree Lagoon and Exotic Fishing Thailand continue operating without adjustment to the season.
Giant snakehead fishing in the wild canals and paddy margins around Bangkok begins its wet-season surge in May. The species thrives in warm, oxygenated, slightly rising water. Surface lures, rubber frogs, and large popping bugs all produce. As the first rains flood marginal vegetation, snakehead move into shallow, weedy areas that are impassable to anglers in the dry season. This is when boat-based snakehead fishing really opens up.
Wild Freshwater — Rivers Awakening
May is the beginning of something interesting for wild freshwater fishing across Thailand's river systems. The first serious rain events of the monsoon do two things: they cool the water slightly after April's peak heat, and they begin re-oxygenating river systems that were sluggish and low. Fish respond.
Giant freshwater stingray in the Mae Klong and Chao Phraya river systems are a May target for specialist anglers. The species is present year-round but becomes more active as river conditions shift with early rains. Guides operating on these rivers typically have May availability at lower cost than high-season months.
Barramundi in wild estuarine and coastal systems around the Gulf begin their wet-season movement in May. Lure fishing in brackish mangrove systems — accessible from Hua Hin and the Gulf coast — can be productive on incoming tides.
May rewards the angler willing to pivot — from the Andaman to the Gulf, from resort lakes to wild rivers rising with the first real rain.
Saltwater Fishing This Month
Andaman Sea — Effectively Closed
Most reputable Andaman offshore charter operators have ceased long-range liveaboard operations by May. The Similan Islands national park is closed to recreational use during the wet season for marine recovery. The Burma Banks and outer sailfish grounds are inaccessible to day-charter vessels in typical May sea conditions.
Some inshore Andaman fishing continues — Phang Nga Bay's sheltered limestone karst channels offer barramundi and snapper fishing that is viable even in deteriorating coastal weather. Operators based in Phang Nga who know the inner bay intimately can put together productive sessions on days when the outer sea is rough.
The GT popping and sailfish season is definitively over for this cycle. The Andaman will not reopen for serious offshore until October at the earliest, and peak season doesn't resume until November or December.
Gulf of Thailand — The Continuing Story
The Gulf is May's saltwater story. Protected by the Thai-Malay peninsula from the southwest monsoon's direct energy, the Gulf's fishing conditions in May are often excellent. Koh Samui and the Samui Archipelago are a strong base for Gulf fishing in May.
Top Cats Koh Samui maintains operations through the wet season. Barramundi are a reliable target; the Gulf's reef structures hold healthy populations of snapper and grouper; and pelagic species — wahoo, queenfish, and Spanish mackerel — move through productive areas on trolling runs.
Hua Hin on the western Gulf coast is accessible from Bangkok (three hours by road) and offers a quieter, lower-cost alternative to Koh Samui–based Gulf fishing. Local charter operators run half-day and full-day trips for reef species and occasional pelagics.
The Gulf of Thailand fishing guide is the essential reference for navigating the region's options through the wet season.
Recommended Trips This Month
1. Bangkok Pay-Lake Overcast-Day Sessions — Overcast or lightly raining May days are the best pay-lake conditions of the wet half-year. Book Bungsamran Lake for a full-day session when cloud cover is forecast. Fish longer, fish more comfortably, catch more.
2. Gulf of Thailand from Koh Samui — A four- or five-night trip based at Koh Samui with two days of Gulf fishing. Fewer crowds than high season, lower accommodation prices, and productive water. Good value in May.
3. Mae Klong Stingray Expedition — Book a specialist guide for giant freshwater stingray on the Mae Klong River, two to three hours southwest of Bangkok. May is a viable month for this specialist pursuit, and guide availability is often better than in the high season.
4. Phang Nga Bay Inshore Barramundi — If you're in Phuket for non-fishing reasons and want a fishing day, book an inshore Phang Nga Bay charter for sheltered-water barramundi. Don't try to go offshore.
What to Avoid This Month
Avoid booking any offshore Andaman trip that depends on open-sea conditions without extensive local verification. What a charter company's website says about "year-round operation" and what conditions are actually like in May are often very different things. Confirm sea state, confirm operator schedule, and read the weather forecast for the week before you commit.
Don't expect northern highland reservoirs to fish the way they did in January. Water is warming, rising, and in some systems beginning to colour with the first runoff. May is not the month to travel specifically for northern reservoir fishing.
Avoid fishing alone in unfamiliar wild river systems in May. Rising rivers and slippery banks in the first monsoon rains are a genuine safety consideration. Fish with a guide or at least with a knowledgeable local companion.
Comfort and Gear Notes
May adds rain to April's heat and humidity. You are now operating in genuinely tropical wet-season conditions. A lightweight packable rain jacket is essential — afternoon squalls can appear with little warning and last from ten minutes to two hours. Waterproof phone pouches are practical for boat-based sessions.
Sun protection clothing remains critical — overcast skies in the tropics do not block UV effectively. Don't abandon your sun shirt and buff just because the sky is grey.
For freshwater sessions in the monsoon transition, the monsoon season fishing strategy guide is worth reading in full. It covers tactical adjustments for rising water, coloured rivers, and the specific opportunities that the wet season opens up.
Non-stainless tackle corrodes faster in humid conditions. Rinse reels and rod guides with fresh water after every session and dry before storage. The wet season is hard on equipment that isn't maintained.
Where to Go Next
June takes May's transition and runs with it — the Andaman is fully closed, wild freshwater fishing improves as rivers rise and pulse, and Bangkok's pay-lakes offer bargain pricing to anglers willing to brave the wet season. See our June fishing guide for how the rainy season fishing settles in.
For the prior month's conditions, see April. The monsoon season fishing strategy and Gulf of Thailand fishing guide are the essential resources for planning trips during the wet half of the year.
