Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 9:07 PM GMT on December 06, 2010
Colombia's heaviest rains in history triggered a landslide in the poor hillside community of Bello on Sunday, killing at least 20 people and leaving 125 missing. This year's unprecedented rainy season had already killed 176 people prior to Sunday, making it one of the deadliest flooding years in Colombia's history, according to the director of Colombia's national disaster management office, Luz Armanda Pulido. In 2009, 110 people died in flooding disasters, and 48 were killed in 2008, according to Colombian Red Cross director of national relief operations Carlos Ivan Marquez. This year's rains are the heaviest in the 42 years since Colombia's weather service was created and began taking data, agency director Ricardo Lozano said. The resulting flooding has destroyed or damaged the homes of 1.6 million people. Colombia's president Juan Manuel Santos said the number of homeless from the flooding could reach 2 million, and said "the tragedy the country is going through has no precedents in our history." Neighboring Venezuela has also been hard-hit by this year's severe rainy season--at least 30 people are dead from floods and mudslides, and tens of thousands homeless. More rain is in the forecast--the latest forecast from the GFS model (Figure 2)--calls for an additional 4 - 6 inches (100 - 150 mm) across much of western and northern Colombia in the coming week.
Figure 1. Satellite-observed rainfall over Colombia during the past two weeks shows a region of 100 - 200 mm (4 - 8 inches) has fallen near Medellin, close to where Sunday's landslide in Bello occurred. 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 La Niña, which is at the borderline between the "moderate" and "strong" categories, is largely to blame for Colombia's deadly rainy season.
Figure 2. Rainfall forecast from today's run of the GFS model predicts that region to the north and west of Bogota, Colombia may see another 100 - 150 mm (4 - 6 inches) during the coming week (red colors.) Image credit: NOAA/CPC.
See also my November 22 post, Colombia rainy season floods kill 136.
I'll have a new post on Wednesday.
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