Monsoon in Srilanka
The North-east monsoon will be active in Sri lanka around November. This is not nearly as heavy as the South-West monsoon in May and June.
During the North-east monsoon the dark clouds gather in the afternoon and usually the showers come down in the late afternoon.
If you are planning your holiday during the monsoon, you will still have dry mornings and the early afternoons to do things and visit sites. You can start and finish the days early and watch the downpour over a bottle of beer.
These heavy rains are welcome by the local farmers, the animals & the vegetation. The farmers start their work in the fields, the animals tend to come out to the water wholes and trees turn dark green.
This is a very pleasant sight which could only be seen during the monsoon, a bit like your spring. People think that during the monsoon it rains all day and all night which is furthest from the truth.
On the other hand Rainfall in Sri Lanka has multiple origins. Monsoonal and Convectional rain accounts for a major share of the annual rainfall along with depressions in the bay of Bengal. The main annual rainfall varies from under 900mm in the driest parts (south-eastern and North-western) to over 5000mm in the wettest parts (western slopes of the central highlands). The conventional rains occur in the hill country and the depressions could happen at any time of the year.