Are you going to one of the Spanish intensive course schools? If so, which one? We have students currently in open water, advanced and rescue classes from just about all of them right now. This time of year is their busy season, versus the slow season for virtually everyone else.
As far as a weather forecast it will probably be fairly rainy, especially in the afternoon. This will vary though and forecasts are usually available on some of the cable channels (in English) down there. The upside of the rainy season is the lushness of everything green. The area is situated in areas of both primary and secondary rain forest, lots of which extends to the waters edge. A pair of tennis shoes and good pair of sandals, like Teva's, Sperry's or Columbia's should be all you need as far as footwear goes. Do bring a good insect repellent containing deet and use it prior to going anywhere near the outdoors, especially the rain forest. The mosquitos can be vicious and could also carry dengue fever and, in fairly rare instances, malaria.
As far as safety goes, use caution and common sense, just like you would in the big city here in the states. Most crime there is of the petty variety-meaning theft from tourists. There are the usual vagrants downtown in Quepos, just like in any port town in the Caribbean, south and central America. If you intend to go clubbing, partying or wandering around near the beach at night, do so in the company of others. During the day it's safe to be just about anywhere.
Hope this helps.
