A strong wind and sandstorm or duststorm in northern and central Sudan, especially around Khartoum, where the average number is about 24 a year. The name comes from the Arabic word habb, meaning “wind. ” Haboobs are most frequent from May through September, especially in June, but they have occurred in every month except November. Their average duration is three hours; they are most severe in April and May when the soil is driest. They may approach from any direction, but most commonly from the north in winter and from the south, southeast, or east in summer. The average maximum wind velocity is over 13 m s−1 (30 mph) and a speed of 28 m s−1 (62 mph) has been recorded. The sand and dust form a dense whirling wall that may be 1000 m (3000 ft) high; it is often preceded by isolated dust whirls. During these storms, enormous quantities of sand are deposited. Haboobs usually occur after a few days of rising temperature and falling pressure.