Orographic Rainfall
The big picture presented so far shows that May through October are the rainiest months of the year. In addition to the long seasonal patterns, it explains the typical rainfall pattern on a much shorter daily timescale.
It's well known that clouds build over Costa Rica during the day (during the heating phase) and rain usually falls in the afternoon and evenings (after the warm air has had time to rise and cool). It's also interesting to look at what's happening on a smaller geograpical scale. From April to October tradewinds are blowing across the Caribbean
If the warm moist air could continue unimpeded it would eventually rise as part of the ITCZ circulation pattern, but the mountains of Costa Rica get in the way. Costa Rica's backbone of peaks force the air upwards causing the familiar rising, expanding, cooling clouds and rainfall.
The consistent direction of the wind from the northeast creates a region of heavier rainfall on the Caribbean slopes and over the central mountains. The air continues to move to the southwest, but by the time it reaches Gunacaste, Nicoya and the Pacific much of the moisture has been removed.
The tropical dry forests of Guanacaste and the Nicoya peninsula developed because Costa Rica's central backbone of mountains lifts the warm air that has picked up moisture as it flows consistently towards southwest across the Caribbean. As the warm moist air is driven up it expands, cools and drops its moisture. The air continues to the southwest, but by the time the trades reach the Pacific shores the air is drier and the rains lighter when they do occur.
The big picture presented so far shows that May through October are the rainiest months of the year. In addition to the long seasonal patterns, it explains the typical rainfall pattern on a much shorter daily timescale.
It's well known that clouds build over Costa Rica during the day (during the heating phase) and rain usually falls in the afternoon and evenings (after the warm air has had time to rise and cool). It's also interesting to look at what's happening on a smaller geograpical scale. From April to October tradewinds are blowing across the Caribbean
If the warm moist air could continue unimpeded it would eventually rise as part of the ITCZ circulation pattern, but the mountains of Costa Rica get in the way. Costa Rica's backbone of peaks force the air upwards causing the familiar rising, expanding, cooling clouds and rainfall.
The consistent direction of the wind from the northeast creates a region of heavier rainfall on the Caribbean slopes and over the central mountains. The air continues to move to the southwest, but by the time it reaches Gunacaste, Nicoya and the Pacific much of the moisture has been removed.
The tropical dry forests of Guanacaste and the Nicoya peninsula developed because Costa Rica's central backbone of mountains lifts the warm air that has picked up moisture as it flows consistently towards southwest across the Caribbean. As the warm moist air is driven up it expands, cools and drops its moisture. The air continues to the southwest, but by the time the trades reach the Pacific shores the air is drier and the rains lighter when they do occur.
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