How to read weather forecasts for Southeast Asia — what the numbers really mean
Tropical weather forecasts can be confusing. What does 70% rain probability actually mean? How accurate is the 7-day forecast? A plain-language explainer.
Rain probability does not mean duration
The most misunderstood number in weather forecasting: "70% chance of rain" does NOT mean it will rain for 70% of the day. It means there is a 70% probability that at least some rain will fall at your location during that time period. In tropical Southeast Asia, a 70% rain probability on an afternoon forecast typically means a 1-2 hour thunderstorm — not 7 hours of continuous rain. The morning can be perfectly sunny with 70% afternoon rain probability.
Temperature forecasts
Forecast temperatures are measured in shade at 1.5 metres above ground (WMO standard). In direct tropical sun, the "real" temperature on your skin can be up to 8°C higher. The "feels like" temperature adds humidity and wind effects. In Southeast Asia, the gap between air temperature and feels-like is typically 3-8°C higher due to humidity. A forecast of 32°C can easily feel like 38-40°C when walking in direct sun with 80% humidity.
Forecast accuracy by timeframe
1-2 day forecasts: Highly accurate for temperature, good for rain timing. Trust them for planning. 3-5 day forecasts: Good for temperature trends and general conditions (rainy vs. dry). Rain timing becomes less precise. 7-day forecasts: Useful for trends only. Temperature ranges are reliable but specific rain predictions are low-confidence. 10+ day forecasts: Treat as general guidance, not specific predictions.
What weather models cover Southeast Asia?
ECMWF (European Centre for Medium-Range Weather Forecasts): Widely considered the most accurate global model, especially for tropical rainfall. This is the primary model used by Open-Meteo and Mausam Online. GFS (US Global Forecast System): Freely available, frequently updated, but less accurate than ECMWF for tropical precipitation. JMA (Japan Meteorological Agency): Excellent for typhoon tracking in the western Pacific.
Tropical weather patterns to understand
Daily convective cycle: In the tropics, the most predictable weather pattern is the daily build-up of afternoon thunderstorms. Solar heating in the morning creates thermals that form cumulus clouds by midday and thunderstorms by 2-4 PM. This cycle repeats almost daily during the monsoon. Understanding this pattern helps you plan: mornings are usually drier than afternoons, although Sumatra squalls can bring thundery showers to Singapore before dawn and in the morning.
Frequently Asked Questions
Why does the weather app say 80% rain but it is sunny? ▾
Rain probability applies to a time window (usually 3-6 hours) and a geographic area. The rain may fall nearby but miss your exact location, or it may arrive later in the forecast window. In the tropics, convective storms are highly localized — it can rain heavily 2 km away while you stay dry.
Which weather app is most accurate for Southeast Asia? ▾
Apps using ECMWF data (Windy, Mausam Online, Apple Weather since 2022) tend to outperform GFS-based apps for tropical rainfall. For typhoon tracking, PAGASA (Philippines) and JMA (Japan) are the authoritative sources.