Thailand weather, month by month
Twelve months, two coasts, one city that ignores the rules. Temperatures are averages for the main destinations, not the extremes.
Thailand has two monsoons, so a single monthly average is misleading: January is dry on both coasts, August is the Gulf's best month and the Andaman's roughest, and September is the wettest month on the Andaman. April is the hottest month at 34–38°C.
- Hottest monthApril, 34–38°C
- Wettest (Andaman)September
- Best Gulf monthAugust
- CoolestDecember–January in the north
The short version
Thailand is tropical: it does not get cold, it gets wet or dry. The only place that approaches cold is the far north at dawn in December, where 8–12°C is normal at 2,500 m on Doi Inthanon.
Month by month
January — the best month overall. Dry on both coasts, 26–32°C, cool evenings in the north.
February — still dry, warmer, and the start of haze in the north.
March — hot (34–36°C), Andaman still calm, north getting hazy.
April — the hottest month. Songkran mid-month. Andaman water at its clearest.
May — the monsoon arrives on the Andaman, often late in the month. Gulf still fine.
June — Andaman wet, Gulf dry and quiet. Good value everywhere.
July — similar; the Gulf is the better bet. Short heavy showers.
August — Gulf at its best. Andaman rough. Peak European holiday season, so book ahead.
September — the wettest month on the Andaman. Cheapest hotel rates of the year.
October — transition month. Andaman improving, Gulf deteriorating. Bangkok is fine.
November — the Andaman dries out; the Gulf gets its rain. Yi Peng in Chiang Mai.
December — dry, cool, busy, expensive. Book three to six months ahead.
What the forecasts get wrong
A "90% rain" day in Thailand usually means one heavy downpour in the late afternoon. We do not cancel land tours for rain; we cancel boat days when the marine forecast is for swell above two metres, because that is a safety issue rather than a comfort one.
Does it rain all day in the rainy season?
Rarely. One to two hours, usually mid-afternoon. October on the Gulf is the exception.
How hot does it get?
38°C in April in Bangkok is normal. The heat index is what matters, and it is why we schedule temple mornings rather than afternoons.
Is the north cold in December?
Chiang Mai evenings drop to 15–18°C. The mountains are 8–12°C at dawn. Bring a fleece, not a coat.
The three regions, in one line each
Bangkok and the central plain. Hot year-round. November to February is the only genuinely comfortable stretch, at 25–32°C with low humidity. March to May is 35–38°C and sticky. The monsoon arrives in June and leaves in October, as an afternoon downpour rather than a wet day.
The north. Cooler than Bangkok in the cool season — Chiang Mai drops to 15–18°C at night in December and the mountains to 8–12°C at dawn — and hotter than you expect in April. The haze season is February to April, with March the worst month in most years.
The two coasts. The Andaman sees its rain May to October and its swell with it. The Gulf sees rain October to December. Between them, February and March are the only months where a boat day is reliable on both.
How to read a Thai forecast
Percentages refer to the chance of rain somewhere in the province, not over your head, and a 90% day is usually one heavy hour at 16:00. The number that matters for a boat is swell height, not rainfall, which is why we watch the marine forecast and not the weather app. If the swell is over two metres, the trip does not run, whatever the icon says.
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Written and checked by the Travel Thailand Tour team, Bangkok · Last updated · Prices are per person and were correct at the time of writing.