Heavy rainfall of around 100 mm is likely in parts of the North Central, Central, Sabaragamuwa, Western and North Western provinces, the Department of Meteorology says.
Afternoon thundershowers are expected across most parts of Sri Lanka, while a few morning showers are forecast in the Western Province and Galle and Matara districts.
The public has been advised to take precautions against temporary strong winds and lightning during thundershowers.