A first simulation study for the nonlinear evolution of the thermal self-focusing instability at high latitudes to examine the dependence of the nonlinear effects on the direction of the heater beam is presented. We demonstrate that due to a local heating of the F region anisotropic plasma, field-aligned bunch-scale structures with a strong enhancement of the electron temperature and negative density perturbations inside these structures are developed. The electron temperature increases up to more than 200% of the background when the incident beam is near the magnetic zenith, as observed in the heating experiment at the EISCAT high-latitude facility (Rietveld et al., 2003). The values of the simulated electron temperature enhancements show a strong dependence on the heater beam direction that is in very good agreement with the EISCAT observations.