  We suggest that the deceleration of the relativistic shock by a denser part
of the interstellar medium off line-of-sight produced the observed radio
``flare'' in the early afterglow of GRB990123. We find that this scenario is
consistent with observations if the particle number density of this denser part
of the medium is between $\sim 200$ and $\sim 2\times 10^4$ cm$^{-3}$. Because
of the premature deceleration of part of the shock, the later stage of the
afterglow should decay modestly faster than the powerlaw expected from an
isotropic shock propagation.
