  Supermassive black holes presumably grow through numerous mergers throughout
cosmic time. During each merger, supermassive black hole binaries are
surrounded by a circumbinary accretion disk that imposes a significant (~1e4 G
for a binary of 1e8 Msun) magnetic field. The motion of the binary through that
field will convert the field energy to Poynting flux, with a luminosity ~1e43
erg/s (B/1e4 G)^2 (M/1e8 Msun)^2, some of which may emerge as synchrotron
emission at frequencies near 1 GHz where current and planned wide-field radio
surveys will operate. We find that the short timescales of many mergers will
limit their detectability with most planned blind surveys to <1 per year over
the whole sky, independent of the details of the emission process and flux
distribution. Including an optimistic estimate for the radio flux makes
detection even less likely, with <1 mergers per year over the whole sky.
However, wide-field radio instruments may be able to localize systems
identified in advance of merger by gravitational waves. Further, radio surveys
may be able to detect the weaker emission produced by the binary's motion as it
is modulated by spin-orbit precession and inspiral well in advance of merger.
