There are two seasons in Costa Rica: dry & wet season. Both are unique and wonderful in their own way. 

The dry season, also referred to as the high season, runs from November to April. These months are the most popular for tourists, with warm sunny days and clean, beginner-friendly waves.

The wet season starts in May and runs through to October. During these months there will be some rain but usually only short showers. The upside of this season is that the lineup is less crowded and it is super tropical and lush. The waves are a little bit more challenging, but still suited for all levels of surfers. 

Here is a video between seasons 2020 (filmed in October/November)