Climate of Costa Rica

When talk turns to Costa Rica's climate, hyperbole flows as thick and as fast as the waterfalls which cascade in ribbons of quicksilver down through the forest-clad mountains. English 19th-century novelist Anthony Trollope was among the first to wax lyrical: "No climate can, I imagine, be more favorable to fertility and to man's comfort at the same time than that of the interior of Costa Rica." Merlin the wizard couldn't have conjured the elements into a more blissful climate.

The country lies wholly within the tropics yet boasts at least one dozen climatic zones and is markedly diverse in local microclimates, which make generalizations on temperature and rainfall misleading.

Most regions have a rainy season (May-Nov.) and a dry season (Dec.-April). And the rainfall almost everywhere follows a predictable schedule. In general, highland ridges are wet, and windward sides always the wettest.

When planning your trip, don't be misled by the terms "summer" and "winter," which Ticans use to designate their dry and wet seasons. Since the Tican "summer"--which in broad terms lasts December through April--equates to winter months elsewhere in the Northern Hemisphere, and vice versa, it can be confusing.

Temperatures
Temperatures, dictated more by elevation and location than by season, range from tropical on the coastal plains to temperate in the interior highlands. Mean temperatures hover near 72deg. F on the central plateau, average 82deg. F at sea level on the Atlantic coast and 89deg. F on the Pacific lowlands, and fall steadily with elevation (about one degree for every 100-meter gain). They rarely exceed a mean of 48deg. F atop Chirripó, where frost is frequent and enveloping clouds drift dark and ominously among the mountain passes. You'll definitely need a warm sweater or jacket for the mountains, where the difference between daytime highs and nighttime lows is greatest. Balmy San José and the Meseta Central have an average year-round temperature of 74deg. F.

This being the tropics, the length of daylight varies only slightly throughout the year. Sunrise is around 5 a.m. and sunset about 6 p.m., and the sun's path is never far from overhead, so seasonal variations in temperatures rarely exceed five degrees in any given location.

Everywhere, March to May are the hottest months, with September and October not far behind. Cool winds bearing down from northern latitudes lower temperatures during December, January, and February, particularly on the northern Pacific coast, where certain days during summer (dry season) months can be surprisingly cool. The most extreme daily fluctuations occur during the dry season, when clear skies at night allow maximum heat loss through radiation. In the wet season, nights are generally warmer, as the heat built up during the day is trapped by clouds.

Rainfall
Rain is a fact of life in Costa Rica. The winds and weather of two great oceans meet above Costa Rica's jungles and mountains. Oceans--especially in tropical latitudes--spell moisture, and mountains spell condensation. Annual precipitation averages 100 inches nationwide.

Depending on the region, the majority of this may fall in relatively few days; sometimes less than 15 days a year. The Tempisque Basin in Guanacaste, for example, receives as little as 18 inches in drier years, mostly in a few torrential downpours. The mountains, by contrast, often exceed 150 inches per year, sometimes as much as 25 feet on the more exposed easterly facing slopes! And don't expect to stay dry in the montane rainforests even on the sunniest days, for the humid forests produce their own internal rain as water vapor condenses on the cool leaves and falls.

Generally, rains occur in the early afternoons in the highlands, midafternoons in the Pacific lowlands, and late afternoons (and commonly during the night) in the Atlantic lowlands. Sometimes it falls in sudden torrents called aguaceros, sometimes it falls hard and steady, and sometimes it sheets down without let up for several days and nights. Sounds like England, doesn't it!

Dry season--"summer"--on the Meseta Central and throughout the western regions is December through April. In Guanacaste, the dry season usually lingers slightly longer; the northwest coast (the driest part of the country) often has few rainy days even during wet season. On the Atlantic coast, the so-called dry season occurs January-April.

Even in the rainy season, days often start out warm and sunny, although temporales (morning rainfall) are not uncommon. Like many tropical destinations worldwide, only newly arrived gringos go out without an umbrella after noon during the wet season. Be prepared: in the rainy season, 23 hours of a given day may be dry and pleasant; during the 24th, the rain can come down with the force of a waterfall. The sudden onset of a relatively dry period, called veranillo (little summer), sometimes occurs during July-August or August-September, particularly along the Pacific coast.

Costa rica climate weather, weather in costa rica
The climate of Costa Rica. Costa Rica is unequivocally a tropical country, situated between 8° and 11° North latitude, fairly close to the equator. Although in the mountains above 2000 meters you get much cooler temperatures, the average annual temperature for most of the country lies between 21.7°C (71°F) and 27°C (81°F). The coolest months are from November through January, and the warmest from March through May. San José, the capital, where over a third of the population lives, stands at approximately 1170 meters altitude and has a mean annual temperature of 20.6°C (69°F).

The nation's climate is classically divided into two major seasons: rainy and dry. The dry season runs from January through May and the rainy season from May to November and December. Locally, the seasons were named by the early Spanish colonizers, who compared them to their own Mediterranean climate, calling the dry months "verano" or summer, and the rainy, grey and gloomy months "invierno" or winter. It is interesting to note that some of the coldest temperatures are registered during the early dry season or "summer". Climate is, of course, a complex phenomenon, and there are many aspects of the weather in Costa Rica that are worth examining in more detail, such as the influences of wind, rain, and topography.

Weather in the tropics is essentially a phenomenon of solar radiation and air circulation. Intense heat at the equator puts air in motion, and a worldwide pattern of winds is established. The most famous of these, for Costa Rica, are the north-easterly trade winds, known locally as "alisios". These winds blow with considerable force from December to March and April. These winds, for example, are responsible for carrying moisture in the form of mists to the slopes of the Tilarán mountain range. These mists are what sustain the magnificent cloud forest ecosystem.

Rainfall patterns, although seasonal, vary greatly in intensity across geographical areas. Some locations receive over 6 mts (18 ft) of precipitation per year, while others receive under 1.5 mts (4 ft). Most of the total rainfall for any given site (about 70%) occurs on less than 15 days of a whole year, and will often be experienced as days of torrential downpour. Costa Rica may hold the world record for the amount of rainy days at one site. Hacienda Cedral registered 359 days of rain in 1968.

The topography of the country also has a great influence on the weather patterns of a given locality. As a result the timing of the dry and rainy seasons varies a bit on each slope of the mountain ranges that run from the north-west to the south-east and divide the nation into a Caribbean slope and a Pacific slope.

On the Caribbean slope the rainy season begins from mid to late April and continues through December and sometimes January. The wettest months are July and November, with a dry spell that occurs around August or September. Major storms, called "temporales del Atlantico" occasionally buffet this slope between September and February, when it will rain continuously for several days; but an average rainy season day will begin clear with a few hours of sunshine that will give way to clouds and rain by the afternoon. In contrast, the driest months of February and March, might be almost entirely without rainfall.

On the Pacific slope the rainy season begins in May and runs its course until November. Here again, days often begin sunny and pleasant, with rains coming later in the day. This is a period in which the trade winds coming from the north-east are much reduced in intensity, and as a result storms often come in from the Pacific Ocean in September and October. In the northern half of the country the Pacific slope experiences an intense dry season, in which no rain may fall for several months. The forests of the North-West are to a large extent deciduous, letting their leaves fall in order to conserve water. Winds can be very strong, occasionally reaching speeds of 90 km/hr in the lowlands, although they average more around 20 km/hr. The whole Central Valley, in which the capital is situated, experiences a mild, pleasant dry season that is matched by moderate temperatures for most of the year, and a lower than average amount of rainfall. Early settlers prized the area for both its mild climate and fertile soils. The southern half of the Pacific slope is much wetter than its northern counterpart, with a shorter dry season and longer and heavier afternoon rains in the wet season.

In a discussion of the climate in Costa Rica one cannot omit El Niño, "The Child". It is a poorly understood weather phenomenon that occurs every two to seven years. It is originally detectable as an unusual warming of a section of the Pacific Ocean. In 1997 El Niño struck Costa Rica once again, disrupting normal weather patterns considerably. Some scientists have postulated that this phenomenon might have been partially responsible for the disappearance of several species of frogs in the late 80's, which are extremely dependent on water. Each time it occurs analysts across the world hold their breaths waiting to see the effects it has on different regions, because they can often be disastrous.