The Meteorological Department has said the country would experience hot days and nights in the month of April.
The Department has told the media that the sun will be directly above Sri Lanka on Tuesday (5), which is the cause for the heat wave.
The heat is expected to recede with the onset of the south west monsoon next month.
According to the Department, the World Meteorological Centre had identified the period from 2001 to 2010 as the warmest decade.
Meanwhile, the Northern, North-Central and North-Western provinces are expected to experience high temperatures with an increase of five to 10 degrees this year.