  Bathed in intense ionizing radiation, close-in gaseous planets undergo
hydrodynamic atmospheric escape, which ejects the upper extent of their
atmospheres into the interplanetary medium. Ultraviolet detections of escaping
gas around transiting planets corroborate such a framework. Exposed to the
stellar environment, the outflow is shaped by its interaction with the stellar
wind and by the planet's orbit. We model these effects using Athena to perform
3-D radiative-hydrodynamic simulations of tidally-locked hydrogen atmospheres
receiving large amounts of ionizing extreme-ultraviolet flux in various stellar
environments for the low-magnetic-field case. Through a step-by-step
exploration of orbital and stellar wind effects on the planetary outflow, we
find three structurally distinct stellar wind regimes: weak, intermediate, and
strong. We perform synthetic Lyman-$\alpha$ observations and find unique
observational signatures for each regime. A weak stellar
wind$\textrm{---}$which cannot confine the planetary outflow, leading to a
torus of material around the star$\textrm{---}$has a pre-transit, red-shifted
dayside arm and a slightly redward-skewed spectrum during transit. The
intermediate regime truncates the dayside outflow at large distances from the
planet and causes periodic disruptions of the outflow, producing observational
signatures that mimic a double transit. The first of these dips is blue-shifted
and precedes the optical transit. Finally, strong stellar winds completely
confine the outflow into a cometary tail and accelerate the outflow outwards,
producing large blue-shifted signals post-transit. Across all three regimes,
large signals occur far outside of transit, offering motivation to continue
ultraviolet observations outside of direct transit.
