Showers or thundershowers will occur at several places in Colombo, Kaluthara, Galle and Matara districts in the morning too.
Showers or thundershowers will be expected over most parts of the island particularly in the evening or night, the Department of Meteorology said.
Heavy falls above 100 mm can be expected at some places in the Uva, Sabaragamuwa, Western, Southern, Central and North-central provinces.
Showers or thundershowers will occur at several places in the sea areas extending from Puttalam to Potuvil via Colombo, Galle and Hambantota.
Showers or thundershowers may occur at few places in the sea areas extending from Batticaloa to Mullaitivu via Trincomalee in the evening or night.
Winds will be south-westerly in direction in the sea area around the island with wind speeds reaching 20-30 kmph. Temporarily strong gusty winds and rough seas can be expected during thundershowers, the department said.