The island of Sri Lanka lies in the Indian Ocean, to the southwest of the Bay of Bengal and to the southeast of the Arabian Sea. It is separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait. According to Hindu mythology, a land bridge to the Indian mainland, known as Rama's Bridge, was constructed during the time of Rama by the vanara architect Nala. Often referred to as Adam's Bridge, it now amounts to only a chain of limestone shoals remaining above sea level. According to colonial British reports, this is a natural causeway which was formerly complete, but was breached by a violent storm in 1480. The width of the Palk Strait is small enough for the coast of Sri Lanka to be visible from the furthest point near the Indian town of Rameswaram.The island consists mostly of flat-to-rolling coastal plains, with mountains rising only in the south-central part. Amongst these is the highest point Pidurutalagala, reaching 2,524 metres (8,280 ft) above sea level.

The climate of Sri Lanka can be described as tropical and warm. Its position between 5 and 10 north latitude endows the country with a warm climate moderated by ocean winds and considerable moisture. The mean temperature ranges from about 16 °C (61 °F) in the Central Highlands, where frost may occur for several days in the winter, to a maximum of approximately 33 °C (91 °F) in other low-altitude areas. The average yearly temperature ranges from 28 °C (82 °F) to nearly 31 °C (88 °F). Day and night temperatures may vary by 4 °C (7 °F) to 7 °C (13 °F). During the coldest days of January, many people wear coats and sweaters in the highlands and elsewhere. May, the hottest period, precedes the summer monsoon rains. The rainfall pattern is influenced by monsoon winds from the Indian Ocean and Bay of Bengal: as the winds encounter the mountain slopes of the Central Highlands, they unload heavy rains on the slopes and the southwestern areas of the island. Some of the windward slopes receive up to 2,500 millimetres (98 in) of rain each month, but the leeward slopes in the east and northeast receive little rain. Periodic squalls occur and sometimes tropical cyclones bring overcast skies and rains to the southwest, northeast, and eastern parts of the island. Between December to March, monsoon winds come from the northeast, bringing moisture from the Bay of Bengal. Humidity is typically higher in the southwest and mountainous areas and depends on the seasonal patterns of rainfall, and places like Colombo experience daytime humidity above 70% all year round, rising to almost 90% during the monsoon season in June. Anuradhapura experiences a daytime low of 60% during the monsoon 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%.