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Climate

The climate is tropical and warm because of moderating effects of ocean winds. Mean temperatures range from 17 °C (62.6 °F) in the central highlands, where frost may occur for several days in the winter, to a maximum of 33 °C (91.4 °F) in low-altitude areas. Average yearly temperatures range from 28 °C (82.4 °F) to nearly 31 °C (87.8 °F). Day and night temperatures may vary by 14 °C (57.2 °F) to 18 °C (64.4 °F).

The rainfall pattern is influenced by monsoon winds from the Indian Ocean and Bay of Bengal. The "wet zone" and some of the windward slopes of the central highlands receive up to 2,500 millimetres (98.4 in) of rain each year, but the leeward slopes in the east and northeast receive little rain. Most of the east, southeast, and northern parts of Sri Lanka constitute the "dry zone", which receives between 1,200 and 1,900 mm (47 and 75 in) of rain annually.

The arid northwest and southeast coasts receive the least rain at 800 to 1,200 mm (31 to 47 in) per year. Periodic squalls occur and sometimes tropical cyclones bring overcast skies and rains to the southwest, northeast, and eastern parts of the island. Humidity is typically higher in the southwest and mountainous areas and depends on the seasonal patterns of rainfall. An increase in average rainfall coupled with heavier rainfall events has resulted in recurrent flooding and related damages to infrastructure, utility supply and the urban economy.