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By: Dr. Jeff Masters , 2:01 PM GMT on November 22, 2010
Colombia is experiencing its worst rainy season in at least 30 years, with at least 136 deaths over the past few months and 1.3 million people affected by flooding. Heavy rains in the capital of Bogota on Wednesday brought the Bogota River to its highest level in 30 years, and more rain is in the forecast--the latest forecast from the GFS model (Figure 2)--calls for an additional 3 - 6 inches (75 - 150 mm) in the Bogota region over the coming week.
Figure 1. Satellite-observed rainfall over Colombia during the past two weeks shows a region of 300 - 400 mm (12 - 16 inches) has fallen near Bogota. Image credit: Navy Research Lab, Monterey.
Colombia's rainy season usually peaks in October, then gradually wanes in November and December. The heavy rains are due to the presence of the Intertropical Convergence Zone, the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together. When these great wind belts come together (or "converge", thus the name "Convergence Zone"), the converging air is forced upwards, since it has nowhere else to go. The rising air fuels strong thunderstorm updrafts, creating a band of very heavy storms capable of causing heavy flooding rains. This year is a La Niña year, which means there is a large region of colder than average water off the Pacific coast of Colombia. Colder than average water off the Pacific coast enhances rainfall over Colombia, and this year's moderate-strength La Niña is largely to blame for Colombia's deadly rainy season.
Figure 2. Rainfall forecast from the GFS model predicts that Bogota may see another 75 - 150 mm (3 - 6 inches) during the coming week. Image credit: NOAA/CPC.
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