Costa Rica has two seasons: wet "invierno" (winter) November/December - April and dry "verano" (summer) May - November.
Light, comfortable and cotton clothing is best to stay cool in both seasons. Be sure to bring a light jacket and an umbrella during the rainy season! VERITAS is located in the city, so you are able to wear your everyday clothes. However, be wary not to stand out too much -- just as you would in any other city -- to avoid being a target. Bring walking shoes, sandals, a hat, sunblock, mosquito repellant, and a beach towel for your weekend excursions. Bring dressier clothes and shoes for nice restaurants and nighttime clubs.
The locals "ticos" wear mostly jeans and cute shirts, such as a shirt you would wear to impress your parents. The boys wear beach tank tops or t-shirts; where the girls typical wardrobe is jeans, heels, and a dressy shirt. If you want to fit in, pack a pair of jeans or pants. They don't normally wear a lot of shorts, so only bring a couple.