Sri Lanka's climate can be described as tropical, and quite hot. The average temperature ranges from a low of 16 °C (60.8 °F) in Nuwara Eliya in the Central Highlands to a high of 32 °C (89.6 °F) in Trincomalee on the northeast coast (where temperatures may reach 38 °C or 100.4 °F). The average yearly temperature for the country as a whole ranges from 28 to 30 °C (82.4 to 86.0 °F). Day and night temperatures may vary by 4 to 7 °C (7.2 to 12.6 °F). January is the coolest month, especially in the highlands, where overnight temperatures may fall to 5 °C (41 °F). May, the hottest period, precedes the summer monsoon rains. Monsoons play a major role in the share of the annual rainfall. The mean annual rainfall is less than 900 mm in the South-eastern and north-western (driest) parts of the island to over 5000 mm in the western slopes and the central highlands.