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Singapore sits in a tropical climate zone where high temperatures and very high humidity persist year-round. Monthly average temperatures typically range from 26–33°C with relative humidity between 75–90% across all seasons. In these conditions, outdoor air is often warmer and more humid than indoor air — meaning ventilation adds heat and moisture rather than removing it. Natural ventilation in Singapore serves mainly for air quality and CO₂ management rather than temperature reduction; air conditioning is the practical primary cooling tool.
The most useful ventilation windows in a tropical climate are during and immediately after rain events. Tropical showers temporarily lower both temperature and humidity, and the 30–60 minutes following a rainstorm are often the best outdoor conditions of the day. Morning hours before solar heating peaks — typically 5–8 AM — offer the lowest overnight temperatures of the day. Air quality is the primary variable to monitor: seasonal haze from agricultural burning, traffic particulates, and industrial pollution events can push AQI above safe ventilation thresholds even when temperatures would otherwise favour opening windows. The real-time AQI component of OpenWindow.live is especially important in tropical cities like Singapore.
In May, the warmest month in Singapore, afternoons reach 31 °C on average and nights fall to 25 °C. The coolest air arrives between 05:00 and 08:00 (25 °C on average): that is when opening the windows cools the home fastest.
On the hottest nights the outdoor air may stay warmer than indoors — open only if it is cooler outside, and close again by 08:00.
Fine particles (PM2.5) are usually lowest around 06:00 (12 µg/m³) and highest around 16:00 (23 µg/m³).
| Month | Avg high | Avg low | Humidity | Coolest hours | PM2.5 |
|---|---|---|---|---|---|
| January | 29 °C | 23 °C | 87% | 05:00–08:00 | 16 |
| February | 30 °C | 23 °C | 83% | 05:00–08:00 | 15 |
| March | 31 °C | 24 °C | 85% | 05:00–08:00 | 16 |
| April | 31 °C | 24 °C | 87% | 05:00–08:00 | 22 |
| May | 31 °C | 25 °C | 86% | 05:00–08:00 | 18 |
| June | 30 °C | 25 °C | 86% | 05:00–08:00 | 17 |
| July | 30 °C | 25 °C | 84% | 05:00–08:00 | 15 |
| August | 30 °C | 24 °C | 86% | 05:00–08:00 | 13 |
| September | 30 °C | 24 °C | 85% | 05:00–08:00 | 16 |
| October | 31 °C | 24 °C | 86% | 05:00–08:00 | 20 |
| November | 30 °C | 24 °C | 88% | 05:00–08:00 | 17 |
| December | 30 °C | 24 °C | 87% | 05:00–08:00 | 14 |
Data: Open-Meteo historical archive, hourly averages 2021–2025 (air quality 2023–2025), local time.
How to air your home in winter in Singapore without condensation and mould →
In Singapore, the best ventilation times are typically early morning (5–8 AM) and late evening (after sunset) when outdoor temperatures drop below indoor levels.
Yes, in most weather conditions. Open windows can drop indoor temperature by 2–5°C in 30 minutes if outdoor air is cooler. Check the live recommendation above for tonight.
Above 80% humidity, opening windows can make indoor air feel sticky. Combine with dehumidifier or wait for drier hours.