The Department warned that some areas could experience rains of over 150 mm, and those living in low lying areas should relocate themselves to higher grounds, reports Xinhua news agency.
An alert on severe lightnings was also issued and motorists were advised to be cautious.
The Disaster Management Centre said that air, land and sea forces were on alert and would assist in evacuation operations if the situation worsened.
Sri Lanka faces severe floods during its annual monsoon season which leaves thousands displaced and casualties.
–IANS
ksk/