San Juan, Costa Rica has a mild climate year-round. From January to May and September to December, temperatures range from 17°C to 31°C, with average highs around 23°C, indicating warm days with occasional cooler nights. June to August sees similar temperature fluctuations, but averages slightly lower at 22°C. The coolest months are October and November, with temperatures dipping slightly below the average high of 29°C. Overall, San Juan experiences a relatively consistent climate without extreme variations throughout the year.