The 19-year-old striker is yet to make a senior appearance for Everton but twice featured in the Premier League club's Under-23 side that played in the EFL Trophy this season.
Southport-born Brewster, an Everton academy player since he was 12, had a previous loan spell at Stockport.
He is available to make his Southport debut against Wrexham on Sunday.
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Everton teenager Delial Brewster has joined National League side Southport on loan until the end of the season.