This paper concerns a continuous structural health monitoring method to detect and track evolution of damages, which may cause changes in structural dynamics. A short-time Fourier transform-based simple scheme is developed to extract the time-varying mode shapes and the mode curvatures from ambient vibration data measured at multiple points. Numerical experiments show that the proposed monitoring method is capable to identify the changes in mode curvatures, which can indicate the location of the damages as well as time when they occur.