  We study the hydrodynamic evolution of an explosion close to the stellar
surface, and give predictions for the radiation from such an event. We show
that such an event will give rise to a multi-wavelength transient. We apply
this model to describe a precursor burst to the peculiar supernova iPTF14hls,
which occurred in 1954, sixty year before the supernova. We propose that the
new generation of optical surveys might detect similar transients, and they can
be used to identify supernova progenitors well before the explosion.
