← Weather & seasons in Thailand
On the thirty-year normal, Bangkok’s driest and coolest month is December (11.6 mm, 23.2°C mean daily minimum) and its wettest is September (335.9 mm). April is hottest at a 35.7°C mean daily maximum. September–October is also the highest flood-risk window for low-lying property. Bangkok’s cool season is real but mild — nothing on this page’s coolest reading would register as cold outside the tropics.
The season bands, honestly
These bands combine the measured normals for WMO station 48455 (Bangkok Metropolis) with the published monsoon calendar, so the trade-offs are visible rather than compressed into one “hot, rainy, cool” label.
| Window | Measured conditions | What that means here |
|---|---|---|
| Nov – Feb | Driest, coolest window. December is coolest overall (23.2°C mean daily minimum) and driest (11.6 mm). | The season most guides call best, and the numbers back it up — with the honest caveat below about what 'cool' actually means here. |
| Mar – May | Heat climbs to the April peak (35.7°C mean daily maximum). Rain still low but rising. | The hardest stretch to be outdoors for long. Songkran falls in mid-April. |
| Jun – Aug | Southwest monsoon established. Rain and humidity both high. | Frequent afternoon downpours, often short. Fewer crowds, lower hotel rates. |
| Sep – Oct | Peak rain — September is wettest on record at 335.9 mm. | The highest flood-risk months for low-lying and ground-floor property. See the flooding guide below before committing to a lease or purchase in this window. |
All figures are 1991–2020 normals. The “what that means here” column is our own reading against the published monsoon calendar, not a separate data source.
What 'cool season' really means in Bangkok
Set expectations correctly before anything else. Bangkok’s coolest month on the thirty-year normal is December, at a 23.2°C mean daily minimum. That is the overnight low, on average, across an entire month — not a cold snap, a mild evening. The genuine change through the cool season is a drop in rainfall and humidity and more comfortable daytime highs, not the arrival of anything a visitor from a temperate climate would recognise as winter. Pack for heat year-round; treat the cool season as a comfort improvement, not a different climate.
Rain, and what it means for property
September is Bangkok’s wettest month on record, at 335.9 mm, inside the southwest monsoon window the Thai Meteorological Department places roughly from mid-May to mid-October. That is also, unsurprisingly, when flood risk is highest for low-lying streets, sois prone to standing water, and ground-floor units. Anyone weighing a lease or purchase against flood exposure should treat a dry-season viewing as incomplete information and read the flooding and monsoon season guide before committing.
What we could not confirm
- A full monthly rainfall or temperature table beyond the extreme months (wettest, driest, hottest, coolest). The archive that would supply every other month could not be reached from this run.
- A Bangkok-specific PM2.5 exceedance-day breakdown by month. The Pollution Control Department's 2025 briefing gives an annual regional figure, not a month-by-month one.
- Any official district-level flood-frequency data. Flood risk varies enormously by soi and drainage, and this page does not attempt a citywide map — see the flooding guide for what is and is not known there.
Frequently asked questions
December, on the numbers — the driest month of the year at 11.6 mm and the coolest by mean daily minimum at 23.2°C. November and January are close behind. This is also the most popular and most expensive stretch to book, for the same reason everyone else is reading the same climate data.
Not in any global sense — this is the single most important honesty check on this page. December's coolest daily-minimum mean, 23.2°C, is warmer than a mild spring evening in most temperate cities. What changes through the cool season is humidity and rainfall dropping, and daytime highs becoming more tolerable, not the arrival of anything a visitor from a four-season climate would call cold. Pack for warm weather year-round; the cool season difference is comfort at the margins, not a different climate.
The measured rainfall peak is September, at 335.9 mm on the thirty-year normal, with August and October close behind — the core of the southwest monsoon season the Thai Meteorological Department places roughly mid-May to mid-October. That is also, unsurprisingly, when flood risk is highest for low-lying streets and ground-floor units. If a property decision depends on flood exposure, read the flooding and monsoon season guide on this site before signing anything, rather than judging a unit on a dry-season viewing alone.
April is hottest on the thirty-year normal, at a 35.7°C mean daily maximum — slightly cooler than Chiang Mai's April mean of 36.7°C, which surprises people who expect the north to be the cooler city. Humidity in Bangkok, at sea level and dense with concrete, tends to make the same temperature feel harder to bear than the same reading inland.
Yes, though less severe by the regional data available. The Pollution Control Department's 2025 haze briefing lists 2024 days over Thailand's 24-hour PM2.5 standard of 37.5 micrograms per cubic metre for Bangkok and vicinity at 97 — lower than the North's 129 and the Northeast's 113, but still substantial, and Bangkok has no equivalent of Chiang Mai's open-burning ban because the sources of its haze are different (traffic and industry rather than agricultural burning). The dry, cool months that make the best weather window are also the months this haze tends to build, the same overlap the north sees in a sharper form.
Related guides
- Flooding & monsoon season — what standing water risk means for ground-floor and low-lying property.
- Air quality in Thailand — the PM2.5 standard and the seasonal pattern.
- Compare Thai cities — the same normals for twelve stations, side by side.
- Chiang Mai vs Bangkok
- Weather & seasons in Thailand — the country-wide picture this page zooms in on.
- Explore Thailand — the section this guide sits in.
Timed your visit. Now time the move.
If Bangkok is more than a trip, see what is actually listed here before the next monsoon sets your calendar.
Sources & References
- WMO Climatological Standard Normals 1991–2020 — Thailand station data sheets (NCEI Accession 0253808), Bangkok Metropolis station 48455: annual rainfall of 1,702.2 mm over 105.3 rain days, wettest month September (335.9 mm), driest month December (11.6 mm), hottest month April at a 35.7°C daily-maximum mean, coolest month December at a 23.2°C daily-minimum mean, annual sunshine 2,212.2 hours
- Thailand government portal, citing the Thai Meteorological Department — the southwest monsoon covers Thailand from about mid-May to mid-October, bringing humid air and general cloud and rain; the northeast monsoon runs from about mid-October to mid-February, bringing clear skies, cool air and dry conditions
- Pollution Control Department (Ministry of Natural Resources and Environment) — Air Quality Situation and Measures for Haze Prevention and Mitigation in 2025 briefing: Thailand's 24-hour ambient PM2.5 standard is 37.5 micrograms per cubic metre; days exceeding that standard in 2024 for Bangkok and vicinity were 97, against North 129, Northeast 113, Central 101 and West 84
Primary and official sources are cited above. Government rules, fees and procedures in Thailand change over time and vary by office; always confirm current requirements with the relevant authority before relying on them. BAANLYY never takes paid placement in editorial content.
