LJ40 Captain on approach to Runway 28L at SFO reports a TCAS RA with a LR60 on approach to Runway 28R. Both aircraft were in VMC and the LR60 crew had the LR40 in sight and turned away.

Narrative

Flying the ILS 28L SFO in VMC; airport not in sight; descending into IMC received a traffic alert followed immediately by 'descend' RA from TCAS system. Right seat pilot and passenger on right-hand side of aircraft observed an LJ60 in apparent climbing right turn away from right side of our aircraft; somewhat aft. This occurred at about the same time we entered the cloud bank. The RA terminated almost immediately as we entered the clouds but no 'clear of conflict' was ever annunciated. Continued descent through cloud bank; acquired airport visually and landed without further incident. [We] were asked to expedite clearing the runway due to B777 on short final behind us. Upon questioning the Tower as to circumstances; they replied that the [LJ60] had us in sight; was talking to NORCAL Approach; and frequency congestion had prevented a traffic call to our aircraft from the Tower. No loss of separation occurred according to the Tower and NORCAL since the [LJ60] crew had stated that they had us in sight. The ILS 28R was NOTAM'd as glideslope inoperative and no approaches were being flown to that runway. This; and the fact that the weather was changing back and forth from IFR to marginal VFR resulted in speed restrictions and vectors for separation/spacing throughout the STAR (Modesto Three). The only way to have avoided this situation was for the [LJ60] not to have been allowed to maneuver VFR along/near the approach path in marginal conditions in a high density traffic environment. The [LJ60] aircrew was apparently not diligent enough in maintaining separation while maneuvering in close proximity to the approach path.