Rainfall
Annual 2540 mm to over 5080 mm in south west of the Island. Less than 1250 mm in the north west and south east of the Inland.
Rainy Seasons
South West Monsoon- May to August
Agriculture in the north and east suffers badly during the South-west Monsoon because the moisture bearing winds dry out as they descend over the Central Highlands, producing hot, during and often very strong winds. Thus June, July and August are almost totally rainless throughout the Dry Zone. For much of the time a strong, hot wind, called yalhulanga by the Sinhalese peasantry and kachchan by the Tamils, desiccates the land.
Nearby three quarters of Sri Lanka lies in what is widely known as the 'Dry Zone', comprising the northern half and the whole of the east of the country. Average annual rainfall in this region is generally between 1,200-1,800 mm. In comparison with many parts of Europe this may not seem unduly dry, but like much of SE India, virtually all of the region's rain falls in the 3 months of the north-east Monsoon between October and December. The rain often comes in relativity short but dramatic bursts. Habarana, for example, located in the Dry Zone between Polonnarywa and Anuradhapura received 1,240 mm (nearly 50") of rain in the 3 days around Christmas in 1975. These rains caused catastrophic floods right across the Dry Zone.
The Wet Zone also receives some rain during this period, although the coastal regions of the South-west are in the rain shadow of the Central Highlands, and are much drier than the North-east between November and January. The South-west corner of Sri Lanka, the Wet Zone, has its main wet season from May to September, when the South-west Monsoon sweeps across the Arabian Sea like a massive wall of warm moist air, often over 10,000m thick. The higher slopes of the Central Highlands receive as much as 4,000 mm during this period, while even the coastal lowlands receive over 500mm.
From the October to December cyclonic storms often from over the Bay of Bengal, sometimes causing havoc from the southern coast of India northwards to Bangladesh. Sri Lanka is far enough south to miss many of the worst of these, but it occasionally suffers major cyclones. These generally come later in the season in December and January and can cause enormous damage and loss of life.
Sri Lanka is affected by two monsoons that sweep over parts of the country at different times. In general, there are two seasons Monsoon and Dry, with the climate remaining hot, humid and wet throughout the year.
Rain is common all year round and an umbrella is useful whatever time you visit.
Southwest Monsoon - arrives in May bringing heavy rains to south and central areas. During this time, temperatures can soar above 35oC in the coastal regions of the south.
Northeast Monsoon - arrives in October and lasts until January. The wet season turns the northern countryside lush green with tropical vegetation and the vibrant colours can make this a wonderful time to visit despite the rain.
Inter-Monsoon - heavy rain and thunderstorms are commonplace in south and central areas during September and November.
It is advisable to carry a lightweight jumper as it can be chillingly cold inside air-conditioned buildings.
The South & Southwest
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The Central Hill Country
Ecological zones The pattern of life in Sri Lanka depends directly on the availability of rainwater. The mountains and the southwestern part of the country, known as the "wet zone," receive ample rainfall (an annual average of 2500 millimeters). Most of the southeast, east, and northern parts of the country comprise the "dry zone, which receives between 1200 and 1900 mm of rain annually. Much of the rain in these areas falls from October to January; during the rest of the year there is very little precipitation, and all living creatures must conserve precious moisture. The arid northwest and southeast coasts receive the least amount of rain—600 to 1200 mm per year—concentrated within the short period of the winter monsoon.
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