SFO Tower Controller voiced concern regarding NCT's handling of a simultaneous arrivals to Runways 28L/R during rapidly changing weather conditions; suggesting NCT should have sent the second aircraft around earlier.

Narrative

Aircraft X checked in on 4 mile final Runway 28L said they just picked up the airport inside the bridge; Aircraft Y was staggered about 1/2 mile in trail for Runway 28R. The weather was shaky at best; but changing rapidly; so every now and then visual separation could not be used. I called out to Aircraft Y; but they were not there. I believe my coordinator called the final sector to get them. We could not see Aircraft Y and assumed they could not see Aircraft X and approach would be taking them out. They kept descending. This is a systemic issue when Approach Control works traffic in SFO Tower's airspace on final attempting to get visual separation. Aircraft Y checked in high on a 2 1/2 mile final 1;500; Aircraft X was a 2 mile final at 800. The first words out of Aircraft Y were 'we are visual now with traffic in sight.' Recommendation; when conditions are rapidly changing; and the aircraft are not able to see the traffic or airport as needed by the final approach fix; break them out.