The bullseye precipitation pattern depicted in the top image occurs because these storms are short-lived and dump large amounts of rain very quickly in one area.

The curl at the bottom occurs because the down-drafting winds hit the EarthвЂ™s surface and spread out. Essentially, as large amounts of rain fall, the large and heavy rain droplets pull the air down with them. The cloud spreads out at ground level due to a strong downdraft, which produces an advancing wedge of condensed water. The photo depicts what is likely a вЂњshelf cloudвЂќ associated with a high-precipitation supercell thunderstorm on the Central Namib west coast, one of the driest regions in Africa. In much of the Namib desert near the coast, less than 20 millimeters of rain fall in a year. Shown in shades of green and blue, rainfall estimates range from 20 millimeters (0.8 inches) to greater than 70 millimeters (2.8 inches). The estimates were made from the Multi-satellite Precipitation Analysis, based on data from the Tropical Rainfall Measuring Mission (TRMM). The map above depicts rainfall for Namibia and South Africa on May 5, 2011. In early May 2011, more rain fell in one day in the Namib desert than typically falls in an entire year.

Even the driest parts of southern Africa have seen exceptional rains and floods. Persistent rains have flooded ephemeral rivers such as the Kuiseb in Namibia and the Boteti in Botswana, which have both reached record highs. Since 2010, rainfall has been above average in many parts of sub-Saharan African-including Angola, Namibia, Tanzania, Cameroon, Congo, and Madagascar-according to the Climate Prediction Center of the U.S.

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