WEATHER · CLIMATE NORMALS · 1991–2020
San José Climate — Averages by Month
What the weather in San José, CRaverages 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 | 17.0 °C · coldest | 112.0 mm |
| February | 17.3 °C | 75.7 mm |
| March | 17.9 °C | 73.5 mm |
| April | 18.8 °C | 109.0 mm |
| May | 18.9 °C · warmest | 361.9 mm |
| June | 18.9 °C | 393.3 mm |
| July | 18.6 °C | 302.3 mm |
| August | 18.6 °C | 351.7 mm |
| September | 18.5 °C | 397.0 mm |
| October | 18.4 °C | 436.4 mm · wettest |
| November | 17.9 °C | 319.0 mm |
| December | 17.4 °C | 178.1 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 San José — centred at 10.00°N, 84.00°W. 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.