  We present a symmetric hyperbolic formulation of the Einstein equations in
affine-null coordinates. Giannakopoulos et. al. (arXiv:2007.06419) recently
showed that the most commonly numerically implemented formulations of the
Einstein equations in affine-null coordinates (and other single-null coordinate
systems) are only weakly-but not strongly-hyperbolic. By making use of the
tetrad-based Newman-Penrose formalism, our formulation avoids the hyperbolicity
problems of the formulations investigated by Giannakopoulos et. al. We discuss
a potential application of our formulation for studying gravitational wave
scattering.
