Sri Lanka's climate can be described as tropical, and quite
hot. Its position between 5 and 10 north latitude endows the country with
year-round warm weather, moderated by ocean winds and considerable moisture.
The mean temperature ranges from a low of 16 °C (60.8 °F) in Nuwara Eliya in
the Central Highlands (where frost may occur for several days in the winter) 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 °F). Day and night
temperatures may vary by 4 to 7 °C (14 to 19 °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.
The rainfall pattern is influenced by the monsoon winds of
the Indian Ocean and Bay of Bengal and is marked by four seasons. The first is
from mid-May to October, when winds originate in the southwest, bringing
moisture from the Indian Ocean. When these winds encounter the slopes of the
Central Highlands, they unload heavy rains on the mountain slopes and the
southwestern sector of the island. Some of the windward slopes receive up to
2,500 mm (98.4 in) of rain per month, but the leeward slopes in the east and
northeast receive little rain. The second season occurs in October and
November, the intermonsoonal months. During this season, periodic squalls occur
and sometimes tropical cyclones bring overcast skies and rains to the
southwest, northeast, and eastern parts of the island. During the third season,
December to March, monsoon winds come from the northeast, bringing moisture
from the Bay of Bengal. The northeastern slopes of the mountains may be
inundated with up to 1,250 mm (49.2 in) of rain during these months. Another
intermonsoonal period occurs from March until mid-May, with light, variable
winds and evening thundershowers.
Humidity is typically higher in the southwest and
mountainous areas and depends on the seasonal patterns of rainfall. At Colombo,
for example, daytime humidity stays above 70% all year, rising to almost 90
percent during the monsoon season in June. Anuradhapura experiences a daytime
low of 60% during the intermonsoonal month of March, but a high of 79% during
the November and December rains. In the highlands, Kandy's daytime humidity
usually ranges between 70 and 79%.