Here is a temperature chart and a rainfall chart which illustrate weather conditions over the course of the last year in the Atenas region of Costa Rica. More particularly, and except for a brief period in early October, they illustrate the conditions where we normally live in a neighborhood called Vista Atenas which is a short distance west of the town of Atenas. For the brief period in October, we were house and cat sitting at the home of friends in a neighborhood called Las Cumbres – a short distance east of the town. The significance of east v. west is revealed by the temperature chart.
As the crow flies, the Las Cumbres location is about 3.7 miles (6 km) from our Vista Atenas location. But, the elevation is about 560 feet (170 m) lower. In Costa Rica, lower altitudes are generally reflected by higher daytime high temperatures and that is borne out by the temperature spike circled in red on the above chart.
As I think I have said before, Costa Rica is a country of microclimates. A few miles one way or the other and a few hundred feet up or down can make a significant difference. If you choose to live in Costa Rica for any length of time, then you should carefully choose the location. Where we live in Vista Atenas, the year 'round daytime highs and overnight lows are comfortable. Neither heating nor air conditioning is required. On rare occasions, heat and humidity can combine to produce a marginally uncomfortable "feels like" temperature. In 2015, that may have happened three or four times.
Costa Rica has two seasons: a wet or “green” season and a dry season. In our area, the dry season normally extends from about mid November of one year to late April or early May of the next. The above chart shows virtually no rain until late April and, excluding an exceptional one day deluge, almost no rain in December. However, in 2015, the wet season was drier than normal. Total rainfall was about 10 inches less than 2014. If the December deluge never happened, then the shortfall would be almost 13 inches less. It must be el niño at work – or maybe even climate change.