The southwest monsoon is expected to set in over Kerala on May 26, the India Meteorological Department (IMD) said in its forecast on Friday.Kerala usually sees the onset of the monsoon around June 1, which then advances northwards covering the rest of the country. This marks the beginning of the monsoon season (June to September) in the country.Last year, the onset of monsoon happened on May 24, according to the department.”This year, the southwest monsoon is likely to set in over Kerala on 26th May” with the possibility that it may happen four days earlier or later than that, the IMD said.