WEATHER · CLIMATE NORMALS · 1991–2020
Surabaya Climate — Averages by Month
What the weather in Surabaya, IDaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | 27.5 °C · coldest | 290.3 mm · wettest |
| February | 27.5 °C | 271.2 mm |
| March | 27.9 °C | 278.0 mm |
| April | 28.3 °C | 196.0 mm |
| May | 28.6 °C | 93.3 mm |
| June | 28.1 °C | 54.6 mm |
| July | 27.7 °C | 26.0 mm |
| August | 27.8 °C | 9.1 mm |
| September | 28.6 °C | 22.9 mm |
| October | 29.2 °C · warmest | 79.5 mm |
| November | 28.9 °C | 188.3 mm |
| December | 28.0 °C | 283.6 mm |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest Surabaya — centred at 7.25°S, 112.75°E. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.