The Disaster Management Centre (DMC) has issued a severe thunderstorm warning, valid through the next six hours.
Accordingly, the provinces expected to be affected are the Western, Sabaragamuwa, Central, Southern, Uva and North-Western provinces.
The DMC said thundershowers, lightning and strong winds could be expected.
Meanwhile, water level in the Kalu river have increased near the Millakanda area in Kalutara, and people in the surrounding areas have been advised to be vigilant.