The average annual rainfall is 1,346 mm (53.0 in), with extremes of 2,500 mm (98.4 in) or more in the mountainous northeast (the windward side of the island) and 500 mm (19.7 in) in the southwestern valleys. The western valleys, along the Haitian border, remain relatively dry, with less than 760 mm (29.9 in) of annual precipitation, due to the rain shadow effect caused by the central and northern mountain ranges. The northwestern and southeastern extremes of the country are also arid.