CLE coordinator witness a loss of separation event when the final controller tried to fill a 7 1/2 mile hole on final and lost separation; wind factors listed as a contributing factor.

Narrative

I was observing the arrival RADAR controller; I was the coordinator. Air Carrier Y was on localizer Runway 24R CLE airport; about 18 miles from runway; at 5000 MSL. Air Carrier X was on vector from the South; 20-40knot tailwind; ground speed approx 250kt. Air Carrier X was descending from 5000 and vectored in front of Air Carrier Y. When Air Carrier X was leaving 5000 controller descended Air Carrier Y to 4000. Gap was minimal in front of Air Carrier Y for this sequence. Air Carrier X was turned to intercept localizer and crossed slightly; allowing Air Carrier Y to get less than 3 miles behind at same altitude. Controller expected Air Carrier Y to get Air Carrier X so that visual separation could be used but he never got Air Carrier X in sight. Air Carrier Y was vectored off localizer to open up the spacing. One or both aircraft was 10+ miles from airport so that our 2 1/2 mile waiver conditions weren't met. Recommendation; arrival controller is still fairly new and hopefully learned from this event. If controller is going to vector an arrival into a 7 1/2 mile gap between 2 other aircraft; he should ensure that altitude separation is maintained since lateral and visual separation are not assured; especially in a strong quartering crosswind. Relying on visual separation to save the day is not good planning.