We consider the problem of monitoring events occurring at discrete locations in a stochastic, time-varying manner. Our problem formulation extends prior work in persistent surveillance by considering the objective of maximizing event detections in unknown, dynamic environments where the rates of events are time-inhomogeneous and may be subject to abrupt changes. We propose a novel monitoring algorithm that effectively strikes a balance between exploration and exploitation as well as a balance between remembering and discarding information to handle temporal variations in unknown environments. We present an analysis proving the long-run average optimality of the policies generated by our algorithm under the assumption that the total temporal variations are sub-linear. We present simulation results demonstrating the effectiveness of our algorithm in several monitoring scenarios inspired by real-world applications, and its robustness to both continuous-random and abrupt changes in the statistics of the observed processes.