We study numerically the disappearance of normally hyperbolic invariant tori in quasiperiodic systems and identify a scenario for their breakdown. In this scenario, the breakdown happens because two invariant directions of the transversal dynamics come close to each other, losing their regularity. On the other hand, the Lyapunov multipliers associated with the invariant directions remain more or less constant. We identify notable quantitative regularities in this scenario, namely that the minimum angle between the two invariant directions and the Lyapunov multipliers have power law dependence with the parameters. The exponents of the power laws seem to be universal. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2150947͔Quasiperiodically forced systems occur in many situations in physics, mathematics, engineering, etc. In many cases, the external quasiperiodic perturbations induce quasiperiodic motions, which correspond to invariant tori. It is important to understand when these invariant tori persist under perturbations, and to identify the mechanisms of their breakdown. It has been known for a long time that the persistence of a torus is related to the exponential growth of the linearization along certain directions (normal hyperbolicity), and that normal hyperbolicity may be lost because of bifurcations such as saddle-node and period doubling, among others. The common feature of these standard bifurcations is that some Lyapunov multipliers approach 1, while the invariant directions remain smooth. In this paper we propose a new mechanism, in which two invariant directions of the linearized dynamics come close to each other, losing their regularity, and the corresponding Lyapunov multipliers remain more or less constant, away from each other and away from 1. Hence, the phenomenon is described by two observables: the minimum angle between the invariant directions and the Lyapunov multipliers. We also identify notable universal power laws of these observables.