This is a video I made during late afternoon yesterday, when we experienced a thunder storm for about 50 minutes. Afternoon rains, which may or may not be accompanied by thunder and lightning, are a common occurrence during our green season. The green season runs from about April to October/November.
Mornings will be sunny, with the clouds moving in sometime in the afternoon. The rain, if we get it, may not last very long, an hour or so. October/November will be the rainiest months. We get periods of a couple of weeks during July and August that are called veranilla or little summer, when we experience no rain.
Costa Rica has many, many microcosms of weather. This is what we experience at our home in Vista Atenas.