Weather in San José in September

A good month. September works. It is not the peak, but nothing about it fights you. You should expect rain on 27 days of the month, which is more days wet than dry.

September ranks 10 of 12 — near the bottom of San José's year. February is the month that works, and the swing between the two is 24 points, which is a different holiday rather than a slightly better one. Worth keeping in perspective: September is the weakest month of San José's year and it is still a perfectly good one. The downside here is small.

Rain on 27 of the month's 30 days, 9 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C; the day barely swings — 5.8 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 27.3 °C and the coldest night fell to 14.4 °C, and the wettest single day dropped 57 mm — roughly 22% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 443 mm against 83 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 256 mm average is a reasonable planning figure, not a promise.

Wind is light at 1.9 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 90%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 23.9 °C in August, 23.3 here, 22.6 in October. Nothing about the timing within the month matters much.

Daylight in September

San José sits close enough to the equator that daylight barely moves all year — 12.2 hours in September, against a range of just 1.2 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

An inland climate

Despite being inland, the year stays fairly even: 12 °C between the year's warmest afternoons and coldest nights. At 1133 m the air is thin enough to matter — sun that burns faster than the temperature suggests, and nights that cool off quickly.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in San José versus nearby

If San José is one option among several, the nearby comparison is worth making. San Isidro is the weaker option in September — 3.1 °C warmer, 1 day less rain. Puntarenas is the weaker option in September — 6.7 °C warmer, 1 day less rain.

So: September is a compromise. February is 24 points better and is what San José is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in San José

See all twelve months in San José, or where else to go in September.