  Neutron stars in astrophysical binary systems represent exciting sources for
multi-messenger astrophysics. A potential source of electromagnetic transients
from compact binary systems is the neutron star ocean, the external fluid layer
encasing a neutron star. We present a groundwork study into tidal waves in
neutron star oceans and their consequences. Specifically, we investigate how
oscillation modes in neutron star oceans can be tidally excited during compact
binary inspirals and parabolic encounters. We find that neutron star oceans can
sustain tidal waves with frequencies between $0.01-20$ Hz. Our results suggest
that tidally resonant neutron star ocean waves may serve as a never-before
studied source of precursor electromagnetic emission prior to neutron
star-black hole and binary neutron star mergers. If accompanied by
electromagnetic flares, tidally resonant neutron star ocean waves, whose energy
budget can reach $10^{46}$ erg, may serve as early warning signs ($\gtrsim 1$
minute before merger) for compact binary mergers. Similarly, excited ocean
tidal waves will coincide with neutron star parabolic encounters. Depending on
the neutron star ocean model and a flare emission scenario, tidally resonant
ocean flares may be detectable by Fermi and NuSTAR out to $\gtrsim 100$ Mpc
with detection rates as high as $\sim 7$ yr$^{-1}$ for binary neutron stars and
$\sim0.6$ yr$^{-1}$ for neutron star-black hole binaries. Observations of
emission from neutron star ocean tidal waves along with gravitational waves
will provide insight into the equation of state at the neutron star surface,
the composition of neutron star oceans and crusts, and neutron star geophysics.
