For those concerned about the weather in Costa Rica, the charts and comments below about the weather in "Vista Atenas" may be of interest.
It is important to note that the temperatures were measured in Vista Atenas near the town of Atenas at an altitude of 2760 ft. (840 m.). Drop a few hundred feet and temperatures are often noticeably warmer. Go up a few hundred feet and temperatures are often noticeably cooler.
The average daytime high was 83.9 °F (28.9 °C). The hottest daytime high was 92.1 °F (33.4 °C) on March 30. The average overnight low was 66.9 °F (19.4°C). The coldest overnight low was 61.0 °F (16.1 °C) on February 4.
All the above temperatures are actual air temperatures. They do not reflect the effect of humidity which, as shown in the next chart, can produce "heat index" or "feels like" temperatures different from the actual air temperatures. Usually, especially during the "green season" with higher humidities, heat index temperatures are somewhat higher than actual air temperatures. - but not dramatically so as can happen in Eastern Canada and the USA during the summertime. On occasion, especially during the "dry season" with lower humidities, heat index temperatures can be less than actual air temperatures.
In 2014, the maximum "heat index" or "feels like" temperature was 94.1 °F (34.5 °C). It occurred on two days during the year (April 29 and July 15) with corresponding humidities of 61% and 64%. The air temperature highs on these days were 87.3 °F (30.7 °C) and 86.7 °F (30.4 °C).
The minimum humidity during 2014 was a desert-like 11%. This occurred on April 2 and resulted in a "feels like" temperature of 86.5 °F (30.3 °C) - a number actually less than the corresponding air temperature high of 90.7 °F (32.6 °C).
Generally, daytime highs in Vista Atenas were accompanied by relatively low humidities. Overnight lows were accompanied by relatively high humidities. But, these result are not characteristic of Costa Rica as a whole. In the Pacific and Atlantic coastal regions, daytime highs are often accompanied by relatively high temperatures and high humidities. "Feels like" temperatures can easily exceed 100 °F (38 °C) even though actual air temperatures may be less.
The wet (or green) and dry seasons can seen on the above chart. From January until near the end of April it was dry with virtually no measurable rain. On April 19 and April 25 there were dribbles. Then, on April 26, came the first deluge – over 2 inches (5 cm) in a short period of time. From May to November, several other deluges occurred, the most dramatic being on August 23 – 3.8 inches (9.7 cm).
Total rainfall during 2014 in Vista Atenas was about 74 inches (187 cm). Some parts of Costa Rica got less. Other parts got much more.