The deflected vortex street found in the wake of a plunging airfoil at high non-dimensional plunge velocities (kh) is investigated by means of a Navier-Stokes solver. The influence of different kinematic parameters on the wake deflection is analysed. The flow field obtained during the transition from a reverse Karman pattern to a deflected pattern is investigated using proper orthogonal decomposition (POD). POD is an efficient technique to decompose the flow field into a set of orthogonal modes of varying energy content. The modal decomposition applied to the unsteady flow field indicated that just 5 modes are sufficient to capture most of the energy. A comparison of the dominant POD modes for different non-dimensional plunge velocities during the transition revealed interesting flow features. © 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.