The climate in San Jose is temperate, with temperatures ranging 65-75 F/18-22 C year-round. The dry summer season runs mid-November to April, and the days are mostly clear. This is Costa Rica's high season, when hotels and attractions are packed and prices are highest.
The rainy season runs from the end of April to early November. Showers and heavy downpours typically occur in the afternoon, though at times it also rains for days on end. Occasionally the streets will flood. Follow the local tradition and carry a fold-up umbrella during the wet season.
In an effort to retain a certain number of visitors despite the cloudy skies, tourism promoters call this time the "green season." It's an appropriate name: During the rainy season, the countryside is lush, and rivers and waterfalls are at their best. Many hotels lower their rates during this season.
The best time to visit San Jose is in early December. Everything is still green, and tourism businesses have just geared up for the high season.