There is a general and common confusion about the relationship and difference between climate and meteorological (or atmospheric) weather. Meteorological weather refers to the description of the conditions in the atmosphere in a particular location at a given time and is measured over a relatively short period of time (hours, days and weeks). The main parameters or variables used to describe meteorological weather are temperature, precipitation, relative humidity, evaporation and evapotranspiration, the direction and velocity of the wind, solar radiation, and atmospheric (or barometric) pressure, among others. The weather is, in general terms, what the communications media refer to in their news programs when they report the probabilities of rain (for the day or for the entire week), daily temperatures, and the formation of different atmospheric systems (depressions, storms, hurricanes, etc.). In comparison, the climate is more complex and less dynamic than meteorological weather.

The climate is a generalization (an average) of the atmospheric conditions and the different biophysical and geographic factors interacting over time and space as measured and observed over a long period of time (usually a minimum of 30 to 50 years). The parameters or variables that define a climate include all of those that are measured and used to analyze meteorological weather, as well as elements such as ocean currents, latitude, elevation, topographical features, the relative distances to oceans and the types of vegetation. The combination of these variables interacting over a relatively long period of time defines the unique characteristics, in climactic terms, of geographic areas, whether a location, a national zone, a continent or a global region.

The location of the island of Puerto Rico puts it at a latitude where it experiences an equatorial tropical climate (Af) in the Köppen climate classification system. This climate classification, developed between 1918 and 1936 by German-Russian geographer, meteorologist, climatologist, and botanist Wladimir Peter Köppen, is methodologically based on the relationship between precipitation, temperature and vegetation. In that sense, the type of climate on the island is characterized by high temperatures and abundant precipitation most of the year. The location of the island and its topography decidedly influence the climate. These elements create the conditions for the development of tropical rain forests, such as El Yunque National Forest, with precipitation of up to 200 inches a year and average temperatures between 70 and 80 degrees Fahrenheit throughout the year. The location of the island places it on the route of the trade winds that come from the north and from east to west. The main effect of these winds on the island’s climate is that the wind usually moves from the northeast to the southwest and, along with the geography of the central mountainous interior (specifically, the part known as the Central Mountain Range), causes what is known as orographic rain (precipitation influenced by topographical relief). Topographical relief influences this kind of precipitation and is produced based on the condensation of water vapor in the clouds and air masses coming from the coastal areas. The air, as it tries to rise along the mountains, becomes cooler and eventually reaches the saturation point (a point close to 100% relative humidity), causing precipitation in the form of rain, which in this case mainly falls on the northern part of the island (north of the Central Mountain Range). Because of this effect, the southern side of the mountains (the southern region of the island) receives substantially less precipitation. This phenomenon explains in broad terms the general characteristics of the landscape and some of the features of its geomorphology, which are influenced by the regional climactic variations seen on both sides of the Central Mountain Range. The northern region is abundantly humid, with dense vegetation and rain forests, with relatively large rivers (compared to those of the southern region of the island) and a more extensive hydrographic network. On the other hand, the southern region is predominantly dry, with a hydrographic network that is sometimes intermittent or ephemeral and with xerophytic vegetation (arid and of low height). These conditions reach an extreme in the Guánica Dry Forest, where an almost constant deficit of rain exists, with only 30 inches (about 762 mm) of precipitation registered annually and an evapotranspiraton of 73 inches (1,854 mm) annually.

In general terms, there is average annual precipitation in Puerto Rico of 69 inches (1,753 mm). However, there are variations in the length and width of the island due to the regional geographic differences. Due to the phenomenon of the trade winds, the northern region of the island usually receives the greatest amount of rain for most of the year, unlike the southern region. There are also differences in the amount of precipitation the western region of the island receives compared to the east. In general, the island experiences what is called a rainy season between the months of May and November (which coincides with the hurricane season) and a relatively dry season between the months of December and April. The average temperature of the island is approximately 80º F (26.7º C). Regional average temperatures do not vary significantly over the course of the year. However, the mountainous region, due to its elevation, registers much lower temperatures on average than those registered in the valleys and the coastal region. The lowest temperature ever registered on the island was 40° F (4.4º C) in areas of the Central Mountain Range, while in the coastal areas the variation in temperature ranges from 80º F (most of the year) up to a little more than 100º F in the summer months.

Author: Harrison Flores Ortiz
Published: February 21, 2016.

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