San José month by month
The reference figures come from Juan Santamaría airport, the valley’s standard station: around 1,971 mm a year, with January at 6 mm and September at 355.
01 Three degrees all year
The Central Valley’s altitude produces what the country sells as eternal spring, and the figures confirm it. At the valley’s reference station, average highs run from 27.1 °C in October to 30.3 °C in April, and lows move between 18.3 and 19.2 °C. That is: three degrees of range across twelve months.
One honest caveat: that station sits at Juan Santamaría airport, some twenty kilometers northwest and slightly lower than central San José. In the city, at just over a thousand meters, highs usually run a degree or two lower. The structure of the year is the same; the exact figure is not.
02 Two seasons and a midsummer lull
Here summer and winter are not spoken of in terms of temperature but of water. The dry season — locally called summer — runs December to April: January records about 6 mm and February about 10. The rainy one, called winter, runs May to November and concentrates virtually all the rest of the 1,971 mm annual total.
Within the rainy season there is a recognized truce: the July lull, when rainfall drops from June’s 280 mm to about 182 and clear mornings return. It is not a guarantee, but it is a pattern reliable enough to plan around.
03 How it rains here
The practical detail matters more than the total. In the Central Valley, wet-season rain is almost always an afternoon affair: sunny mornings, clouds building at midday and a short, heavy downpour between two and five.
That means you can travel in the rainy season without losing the trip, provided you accept one simple rule: outdoor plans happen in the morning, and the afternoon is kept for museums, markets or coffee. September and October, at 355 and 331 mm, are the months when that rule breaks down most often.
Key moments at a glance
Under 15 mm a month and clear skies almost every day.
About 34 mm, a still-green valley and already clean air.
A truce inside the wet season, with more reliable mornings.
Almost 700 mm across the two months and lost afternoons.
04 Verdict
Go between December and March if you want weather certainty: it is the dry season, the expensive one, and the one that lets you chain capital, volcanoes and coast without watching the sky.
July and November are the smart alternatives: fewer people, lower prices and a far greener valley, in exchange for planning around the morning. September and October only pay off if your trip is urban and indoors.
