Namibia extends from 17°S to 25°S latitude: climatically the range of the sub-Tropical High Pressure Belt. Its overall climate description is arid, descending from the Sub-Humid (mean rain above 500 mm) through Semi-Arid between 300 and 500 mm (embracing most of the waterless Kalahari) and Arid from 150 to 300 mm (these three regions are inland from the western escarpment) to the Hyper-Arid coastal plain with less than a 100 mm mean. Temperature maxima are limited by the overall elevation of the entire region: only in the far south, Warmbad for instance, are mid-40 °C maxima recorded.
Typically the sub-Tropical High Pressure Belt, with frequent clear skies, provides more than 300 days of sunshine per year. It is situated at the southern edge of the tropics; the Tropic of Capricorn cuts the country about in half. The winter (June – August) is generally dry. Both rainy seasons occur in summer: the small rainy season between September and November, the big one between February and April. Humidity is low, and average rainfall varies from almost zero in the coastal desert to more than 600 mm in the Caprivi Strip. Rainfall is highly variable, and droughts are common. The last rainy season with rainfall far below the annual average occurred in summer 2006/07.
Weather and climate in the coastal area are dominated by the cold, north-flowing Benguela Current of the Atlantic Ocean, which accounts for very low precipitation (50 mm per year or less), frequent dense fog, and overall lower temperatures than in the rest of the country. In Winter, occasionally a condition known as Bergwind (German for “mountain breeze”) or Oosweer (Afrikaans for “east weather”) occurs, a hot dry wind blowing from the inland to the coast. As the area behind the coast is a desert, these winds can develop into sand storms, leaving sand deposits in the Atlantic Ocean that are visible on satellite images.
The Central Plateau and Kalahari areas have wide diurnal temperature ranges of up to 30 °C.
Efundja, the annual seasonal flooding of the northern parts of the country, often causes not only damage to infrastructure but loss of life. The rains that cause these floods originate in Angola, flow into Namibia’s Cuvelai basin, and fill the oshanas (Oshiwambo: flood plains) there. The worst floods so far occurred in March 2011 and displaced 21,000 people.