MYF Controller described a NMAC between MYF pattern traffic and a NKX military aircraft; the reporter noting this type of event is not infrequent and suggested more information be made available to NKX itinerant operators.

Narrative

I was providing [on the job training] to a developmental on Local Control. The Controller lost the picture and I took over with moderate traffic and complexity. In the midst of the situation I was alerted by the Ground Control that there was traffic in our airspace. I observed a military aircraft opposite direction to my departures and parallel to my downwind overflying at roughly pattern altitude. I saw that it was on a direct course to blindside one of my pattern aircraft so I issued traffic. I don't recall if he acknowledged; so I issued it again. I watched as the military aircraft converged and overflew very slightly ahead of the Cessna. I issued wake turbulence cautions as well. It was one of the closest NMAC's I've ever seen. This frequently happens with itinerant aircraft into NKX; but they are usually much closer to NKX. This is the first time I've had one actually in my pattern; at pattern altitude. They are usually above it. There needs to be a prominent notice in the AFD advising the military pilots into NKX about the danger of swinging wide into the MYF pattern.