In the northern plains and desert region, average temperatures range from 32° C (90° F ) in winter (November to February) to 42° C (108° F ) in summer (March to June); the hottest months are May and June. In the central and southern regions, average temperatures are 27° to 29° C (80° to 85° F ). Rainfall decreases from south to north, the annual average varying from 120 cm (47 in) in the south to less than 10 cm (4 in) in the north; the rainy season is from July to September. Climatic hazards—sandstorms in the northern deserts and flooding rains in the central belt— often interfere with railroad traffic. The most temperate climate occurs in the Red Sea Hills.