Situational Awareness
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Human Factors; Weather
CE750 on the visual approach talking to Tower.  Indicating 180 KT.  M20 on parallel downwind indicating 120 knots. Turned the M20 due north for base to follow the CE750.  Issued traffic then got caught up with oSther duties.  When I looked back the M20 was indicating 180 KTS and the CE750 had slowed to 120 KTS.  I cleared the M20 for the visual approach to the south runway.  M20 did not have the CE750 insight.  I saw the wind was 120@15 figured the turn would slow the M20.  The M20 did not slow.  I issued traffic again but the M20 still did not have the CE750 insight.  I cancelled the M20 approach clearance and broke him out.  I known there was a loss of separation. I miscalculated the winds. I thought they would have helped slow the M20; but I was wrong.  I should have recognized the situation quicker and broke the aircraft out sooner.  Needed to be more proactive than I was.
Tower Controller reports a loss of separation between a CE750 and a M20 during as planned visual approach but with the M20 pilot unable to visually acquire the CE750. The approach speed of the CE750 had decreased 60 KTS and the M20 had increased 60 KTS; which was unexpected.