The very irregular, very brief, rainy season lasts about 1 month as the maximum rainfall is recorded in August, with about . The rainy season is characterized by a seasonal reverse of wind regimes, when the Intertropical Convergence Zone goes northerly. Average annual rainfall is very low, with only  of precipitation. Khartoum records on average six days with  or more and 19 days with  or more of rainfall. The highest temperatures occur during two periods in the year: the first at the late dry season, when average high temperatures consistently exceed  from April to June, and the second at the early dry season, when average high temperatures exceed  in September and October. Temperatures cool off somewhat during the night, with Khartoum's lowest average low temperature of the year, in January, just above . Khartoum is one of the hottest major cities on Earth, with annual mean temperatures hovering around . The city also has very warm winters. In no month does the average monthly high temperature fall below . This is something not seen in other major cities with hot desert climates, such as Riyadh, Baghdad and Phoenix.