Costa Rica has two weather seasons, wet and dry. Due to the micro cilmates your weather will vary greatly depending on where you are in Costa Rica. On the north shore or Lake Arenal the town of Nuevo Arenal receives around 250 annual inches of rain fall, while just across the lake on the south shore at Tilawa Water Sports Center the rainfall is about half that or 140 inches.
The next time you are in Costa Rica and ask about the weather you will always hear the same response, "the weather is always perfect in Costa Rica."