The Shrimpers are currently without first choice stopper Mark Oxley who misses their next three games following his sending-off against Charlton AthleticBCFC
It is a seven-day rolling loan, which initially runs until 22 September 2018.
Stockdale has not figured for Blues since the final game of last season in the 3-1 victory against Fulham.
The 32-year-old was told over the summer that he was not part of Garry Monk's plans moving forwards.
The Shrimpers are currently without first choice stopper Mark Oxley who misses their next three games following his sending off against Charlton Athletic last Saturday.
Oxley was one of two Southend players and one Charlton player who were sent-off in added-time during the Addicks 2-1 victory at Roots Hall following a confrontation between the two teams.
Another 'keeper Ted Smith has been out for more than a year with a shoulder problem. Nathan Bishop, 18, is the only other available 'keeper – he made his first start on Tuesday against Cambridge in the Checkatrade Trophy.
Southend, whose Head Coach is former Huddersfield and Charlton boss Chris Powell, are currently 13th in the table with seven points from their six league matches this season.
They face a stern test later today when they host table toppers Peterborough United, who have won five and drawn one of their opening six games.