This paper studies numerically the temporal development of spatial oscillations in a confined rotating fluid differentially heated from below. It is found that spatial oscillations occur when the internal Rayleigh number is larger than the critical Rayleigh number obtained from linear analysis. Because the internal Rayleigh number depends on the vertical temperature gradient and length scale which are time dependent, the stability of the transient flows cannot be predicted from an external Rayleigh number. The numerical resolutions of boundary layers are discussed.