We simulate the inner magnetosphere during the magnetic storm of September 25, 1998 using the Rice Convection Model with boundary fluxes estimated from geosynchronous data. Model results indicate development of an interchange-like instability in the dusk-to-midnight sector, producing ripple structures in the plasma density, swirls in the subauroral ionospheric electric field pattern, and undulations near the equatorward edge of the diffuse aurora. We suggest that these disturbances might be observable whenever a strong main-phase ring-current injection is followed by a major, sustained decrease in the plasma energy density at geosynchronous orbit, a circumstance that will also produce rapid decay of the storm-time ring current.