  Multiwavelength observations of Type II supernovae have shown evidence for
the interaction of supernovae with the dense slow winds from the red supergiant
progenitor stars. Observations of planetary nebulae and the nebula around SN
1987A show that the slow winds from extended stars frequently have an axisymme-
tric structure with a high density in the equatorial plane. We have carried out
numerical calculations of the interaction of a supernova with such an axisymme-
tric density distribution. For small values of the angular density gradient at
the pole, the asymmetry in the interaction shell is greater than, but close to,
that expected from purely radial motion. If the angular density gradient is
above a moderate value, the flow qualitatively changes and a protrusion emerges
along the axis. For a power-law supernova density profile, the flow approaches
a self-similar state in which the protrusion length is $2-4$ times the radius
of the main shell. The critical density gradient is larger for steeper density
profiles of the ejecta. Most of our calculations are axisymmetric, but we have
carried out a 3-dimensional calculation to show that the protrusion is not a
numerical artifact along the symmetry axis. For typical supernova parameters,
the protrusions take $\gtrsim$ several years to develop. The appearance of the
shell with protrusions is similar to that observed in VLBI radio images of the
remnant 41.9 +58 in M82 and, possibly, of SN 1986J. We also considered the
possibility of asymmetric ejecta and found that it had a relatively small
effect on the asymmetry of the interaction region.
