  We propose an effective model for the superconducting transition in the
high-T_c cuprates motivated by the SU(2) gauge theory approach. In addition to
variations of the superconducting phase we allow for local admixture of
staggered flux order. This leads to an unbinding transition of vortices with
staggered flux core that are energetically preferable to conventional vortices.
Based on parameter estimates for the two-dimensional t-J model we argue that
the staggered flux vortices provide a way to understand a phase with a moderate
density of mobile vortices over a large temperature range above T_c that yet
exhibits otherwise normal transport properties. This picture is consistent with
the large Nernst signal observed in this region.
