We present spectral analysis of early observations of the Type IIn supernova 1998S using the general non-local thermodynamic equilibrium atmosphere code PHOENIX .
We model both the underlying supernova spectrum and the overlying circumstellar interaction region and produce spectra in good agreement with observations .
The early spectra are well fit by lines produced primarily in the circumstellar region itself , and later spectra are due primarily to the supernova ejecta .
Intermediate spectra are affected by both regions .
A mass-loss rate of order \dot { M } \sim 0.0001 - 0.001 { \textrm { M } _ { \odot } } yr ^ { -1 } is inferred for a wind speed of 100 - 1000 km s ^ { -1 } .
We discuss how future self-consistent models will better clarify the underlying progenitor structure .