I think it rains all the time somewhere in Costa Rica. For sure it's humid. The rainy season technically starts in May, but that might be more like shoulder season. It also depends on where you are. The northwest region of Guanacaste on the Pacific side is supposedly one of the driest, and it rained on us every day last May, really coming down, but we generally did see the sun eventually...it seems to rain at the same time of day every day so at least you can count on that. The pouring rain does make for some pretty exciting driving conditions, which were already exciting even in the good weather. The San Jose area may have tendencies more common with the Carribean side. Any trip to Costa Rica is worth it. The country is beautiful. Please do your research ahead of time about driving and get a realistic idea of how long it takes to get to the different areas. I had been planning our whole trip to visit Monteverde, because that's on everyone's list to see, until I realized is was 2+ hours each way on a not very good road. It will be much closer for you from San Jose. Enjoy.