The Yorkshire-born Barbados international winger, 25, will spend the next month at Meadow Lane.
Forte moved from Sheffield United to Glanford Park in July 2007 as part of the deal that took Billy Sharp back to Bramall Lane.
He became a first-choice forward for the Iron at the start of last season following the departures of Gary Hooper and Paul Hayes, but was sold to Southampton in the January transfer window after failing to back up his starts with goals.
At the Iron he featured in 118 competitive first-team games, scoring 11 goals.
He made 10 appearances for Saints, managed by his former Iron boss Nigel Adkins, as they won automatic promotion from League One.
He drifted out of the first-team picture following promotion to the Championship, and made three appearances on loan at Preston earlier this season.