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CLIMATE IN COSTA RICA
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TEMPERATURE
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Due to the fact that Costa Rica is located between 8 and 12 degrees
north of the Equator, we do not suffer the drastic changes of
temperatures between one seasonal period and another, that characterize
the temperate and cold zones. The major part of the Costa Rican
territory enjoys thermal stability throughout the year. In some
zones of Guanacaste, the increase in temperature is associated
with the dry season and the large amount of daylight hours with
clear skies.
Altitudinal Variation
The parameter that does produce temperature changes is the altitude,
and because Costa Rica is a country with great altitudinal variations
( from sea level to more than 3800 meters ), this effect is considered
of great importance. In the highlands the temperatures are low
during the whole year. At high elevations the temperature can
drop many degrees during the coldest hours of the night, ( in
the highest points the temperature can go below 0 C ) but increase
with the sunlight during the daylight.
At the other extreme to this situation are the lowlands, where
temperatures do not descend less than 20 C and not higher than
30 C. In the major part of the Central Valley, the maximum temperature
( around 28 C ) is reached a little after midday and descends
gradually to about 20 C around 7:00 p.m. It stays stable during
the night and reaches the minimum ( around 18 C ) around 4:00
a.m., it overcomes the 20 C point at 7:00 a.m. and increases gradually
to midday.
This pattern of daily oscillation is constant during the whole
year, although, naturally, during the rainy season the temperatures
tend to be lower and descend faster during the afternoon. The
hibernation fronts in december and january make the temperature
descend considerably.
It has been talked of in recent years about global warming of
our planet. The intense industrial outpourings and the growing
world population are in part responsible for some of these changes.
The fact is that a general change in the planets´s temperature
would implicate a change in distribution patterns of rainfall,
in the sea level and other climatic factors all over the world.
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WINDS
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Because Costa Rica is located in the northern hemisphere, the
dominant winds of its climate are the north easterly trade winds.
The Northern Winds
The northern winds are cold and dry winds that blow in our national
territory in December and January. Because of the cold weather
in the North American continent during this time of the year,
the zone of high pressure intensifies to a latitude approx. 30
degrees North and these winds descend to the south reaching our
territory. These cold and dry winds penetrate until the Central
Valley in Costa Rica, producing the typical climate of the end
of the year.
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RAINFALL
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In Costa Rica there are no real dry zones, because the minimum
rainfall is of 1200 mm per year ( 48 inches ). On the other hand,
there are zones with 8000 mm ( 320 inches ) of rainfall per year.
In general terms, in Costa Rica we can talk about 2 rainfall regimes:
The Pacific ( often called tropical ), characterised by a very
well defined dry season, and the Caribbean ( many times called
equatorial ) , with the permanent influence of the north easterly
trade winds and without a dry season.
In the Caribbean regime, there are 2 very different systems. On one side, the
coast lowlands and northern plains, that present a notable decrease of rainfall
during March and April and sometimes September, and on the other side, the mountains
and slopes exposed to the trade winds, where it rains all year long without appreciable
interruption.
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CLIMATE THE CARIBBEAN REGION
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This region, that encompasses the Caribbean and Northern slopes,
present temperatures according to the altitude. The whole region
is directly exposed to the north easterly trade winds, which are
fully loaded with the humidity of the Caribbean Ocean. Part of
this humidity precipitates in the coasts and plains, but the major
rainfall occurs in the slopes of the range of mountains due to
the topographic effect.
This kind of rainfall is due to the winds, that are being forced
to climb because of the mountains, they lose temperature slowly
and create the condensation and the subsequent rainfall.
This rainfall regime will decrease during 2 periods of the year,
March-April and August-September, because of modifications produced
in the tradewinds by the relative position of the sun. Nevertheless,
in these zones there is no defined dry season.
The highest rainfall occurs in the mountains, particularly between
1000 and 2000 meters ( 3000 and 6000 feet ) of altitude, with
major precipitations of 5000 mm ( 200 inches ). The highest amounts
of rainfall have been registered in the cuenca of the Reventazon
River, where 8000 mm ( 320 inches ) fall yearly, and more at other
sites. At altitudes higher than 2000 m ( 6000 feet ) the rainfall
tends to decrease
Storms in the Atlantic
They correspond to a variable period ( up to 15 days ) in which
rain and drizzle predominate that could last all day and night.
They occur mainly during the winter and in the north.
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CLIMATE THE PACIFIC REGION
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The fundamental characteristic of the climate of the Pacific is
the presence of a dry season that lasts for 4 months and more
in some zones. Also there is an important characteristic, a short
dry period during half of the year, known as veranillos ( little
summers )
Rainy Season
During this period, the Pacific region is inside the convergence
zone, where the winds from the west strengths those already existing
and produce the rainy season with all its intensity. This period
extends from mid May to the end of November, and it is only interrupted
by the veranillos. ( little summers ). The veranillos last for
a period of one to two weeks , almost always in July, where precipitation
decreases considerably in all the Pacific Zone. When it occurs
early ( end of June ), its known popularly as " Veranillo
de San Juan ", if it occurs in July or beginning of August,
sometimes with alternatives of dry and rainy days, the countryside
men know it as caniculas. This phenomena, is due, basically to
the changes of the zenithal position of the sun.
Rainfall in the Osa Peninsula
The region of the South Pacific receives considerably more rainfall
than Guanacaste and the north of Puntarenas, and so much more
than many localities of the Caribbean. Nevertheless, different
than the Caribbean, this region has a period with a defined decrease
of rainfall.
Storms in the Pacific
During the summer in the north ( from July to end of November ), frequently, zones
of low pressure are formed in the Caribbean region, where winds are produced that
rotate in opposition to clockwise to the centre of the depression. This produces
strong winds and rain in the Pacific Region that sometimes may turn into hurricanes.
Costa Rica is far away from the preferential route of hurricanes, this is why
we mainly get their indirect effects - to the Pacific Littoral. ( With the exceptions
of Joan in 1983 and Mitch in 1998, that dangerously approached our Caribbean coast,
causing devastating flooding results.)
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