When to Avoid Thailand and Vietnam: A Month-by-Month Risk Guide

There is no single bad month to visit Thailand or Vietnam. There are specific places you should not book in specific weeks. Northern Thailand has a smoke season. The Andaman and Gulf island coasts are wet at opposite times. Central Vietnam takes a long autumn wet season with a flood risk, and the seas around Ha Long Bay carry a summer storm risk. None of it makes a trip impossible. It makes the routing matter. This is the companion to our best time to visit Thailand and best time to visit Vietnam references, read from the other end, so you can keep a group out of the few windows that disappoint. Check it alongside the current entry and visa requirements before you fix dates.

The principle: knowing what not to book

The risk lies in a handful of region-and-month combinations where the place itself underperforms, closes, or floods. A specialist does not steer a client away from a whole country for a season. We steer them away from the wrong coast in May, the wrong hill town in March, the wrong heritage city in November. The rest of the trip stays where it should be.

Northern Thailand: the smoke season, roughly February to April

The single most important thing to plan around in the north is the burning season. From roughly February to April, and usually worst in March, agricultural and forest burning across northern Thailand and the wider region combines with still air. Air quality drops sharply across Chiang Mai, Chiang Rai, Pai, and the surrounding hills. In late March 2026 IQAir put Chiang Mai among the ten most polluted cities in the world. The skies turn hazy, mountain views vanish, and the haze matters for anyone with respiratory sensitivity, for young children, and for outdoor-heavy itineraries. This is not a reason to cancel the north; it is a reason to time it. We steer air-quality-sensitive travellers and trekking-led programmes to the cool season from November to January or the green season from June to October, when the hills are clear and, in the rains, at their greenest.

Thailand's islands: book the right coast, not the right month

Thailand's islands are sellable for most of the year, provided you match the coast to the date, and the expensive mistake is booking the wrong one. The Andaman coast in the west, including Phuket, Krabi, Phi Phi, and Khao Lak, runs on the southwest monsoon and is at its wettest and roughest from about May to October. During those months the Similan and Surin marine national parks, the region's best diving and snorkelling, close to visitors entirely, roughly from mid-May to mid-October. The Gulf coast in the east, including Koh Samui, Koh Phangan, and Koh Tao, runs later and stays drier through the middle of the year, taking its heaviest rain around October to December. The practical rule is simple: for a May-to-September beach stay, lean Gulf, home to our Koh Samui wellness retreat; for a November-to-April one, lean Andaman, where our Bangkok and southern islands programme finishes; and never assume the two coasts share a season.

Central Vietnam: the Hue and Hoi An wet season, September to February

Central Vietnam is where the country's seasonal risk is most concentrated, and it is the leg buyers most often get wrong. The coast around Hue, Da Nang, and Hoi An has the longest wet season in the country. Tropical storms start to arrive in September, and the rain runs until about January around Hoi An and into February around Hue, with cool, grey days. Flooding is most likely from September to November, when sustained downpours raise the rivers. Hoi An's UNESCO old town sits low beside the river and can flood at street level in those weeks, though not every year. In a bad year there are boats in the lanes. September to November is not the time to anchor a heritage stay in Hoi An or a beach extension nearby; December and January are wet but calmer, and workable with indoor options. We move central Vietnam earlier or later in the calendar, or weight the trip toward the north and south, when a client's dates fall into that window.

Ha Long Bay and northern Vietnam: the storm months, about June to September

The Gulf of Tonkin carries a storm risk through the summer, roughly June to September, and storms can reach into October. The risk falls on the one experience clients most want there: the overnight Ha Long and Lan Ha Bay cruises. When a storm system moves in, the port authority can suspend cruise departures on safety grounds, sometimes at short notice, which is the kind of disruption a fixed itinerary cannot absorb gracefully. The bay is still very much in season across summer, and most departures sail; the point is to build in a contingency, not to avoid the dates outright. The other northern caveat sits at the opposite end of the year: from late December to March the bay is cool, cloudy and often misty, softening the famous views into outlines. We hold a flexible day around a summer cruise and set expectations on winter visibility.

The far north of Vietnam: Sapa, Ha Giang, and the mountain seasons

The mountains of the far north, including Sapa and the Ha Giang loop, run on their own calendar and reward precise timing. The best windows are September to November, when the rice terraces turn gold for the harvest and the air is clear, and March to May, when the new rice is a vivid green. Both suit our Northern Vietnam and Sapa Highlands circuit. Two periods need planning around. The first is deep winter, December to February, when cold and persistent fog can obscure the very views people come for, and the highest passes turn cold. The second is the peak of the summer rains, June to August, when heavy downpours raise the risk of landslides and washed-out mountain roads on the loop. For motorbike and jeep itineraries in particular, the road conditions in the wettest weeks are a safety consideration as well as a comfort one, so we time the far north to the shoulder months on either side.

Thailand and Vietnam, month by month: what to avoid

The table is a planning guide, not a guarantee, since exact dates shift year to year. Treat it as the short list of region-and-month combinations to route around, while the rest of each country stays open.

How we plan around it

When a client's dates are fixed, we route around the weather. Send us the fixed dates and we will show you where the route has to bend: a central Vietnam leg moved earlier, an Andaman beach swapped for a Gulf one, a contingency day held around a summer Ha Long cruise, or the north moved out of the haze weeks. When the dates are open, we advise the window that fits the interests; send us a target window or a wish list and we will say which weeks to route around. See also our guide to how many days you need for Thailand and Vietnam.