Costa Rica has a tropical climate with two seasons. The dry season is from December to April and the wet season is from May to November. Weather always varies between regions, some higher altitudes like Monteverde have cooler, wet weather. Manuel Antonio experiences hotter, more humid weather, and while during the day the temperatures can be very warm everything can cool down at night.
Comfortable lightweight clothing is recommended, as well as a sturdy pair of hiking boots and a light rain coat. Layers are recommended for people traveling to many different parts of the country so that you can adapt to every type of weather throughout your trip. If you choose to participate in the optional Canopy or Zipline tours, it is recommended that you wear old or worn clothing.
Tortuguero: For passengers traveling to Tortuguero it is very important to pack rain gear, hiking shoes, and insect repellent in the luggage that will accompany you to Tortuguero.
Costa Rica Average Temperatures: http://www.gate1travel.com/weather/americas/default.aspx#costa-rica-weather