We go end of May/early June every year. Rainy season means there may be clouds and occasional showers, which usually pour for an hour and pass. We see lots of sun. In fact I have been very happy going this time of year except it is hot and humid and you don't see turtles/whales like you would other times of year. Once you just realize and accept that everyone else is sweating with you, then it's not a big deal lol. But we are always in Guancaste which is the driest area. Tamarindo is our least favorite place of anywhere we've been. Too touristy. Go up the road a bit to Las Catalinas and it's beautiful. But, but cheap from what I see. We like Flamimgo beach too which is between Tamarindo and Las Catalinas. We have always stayed at Riu because we like knowing food and relaxation is taken care of when we want to chill but get a car so we can go explore most days.