We investigate periodically amplified transient stripe textures which are spontaneously formed in the asynchronous reorientation regime of a thin homeotropic NLC layer exposed to an in-plane continuously rotating magnetic field. Wavelengths, orientations and ranges of existence of the stripe texture are determined by means of polarizing microscopy. A theoretical model is given which incorporates backflow coupling and stochastic noise. The model eluciates the hydrodynamic pattern formation mechanism and describes the time-periodic characteristics of the structures in good agreement with the experiment.