Observations of the Type II Supernova 1986I in M99

We report spectroscopic and photometric results on a supernova in M99, SN19861, from first detection to several months after the explosion. This supernova is distinct from other supemov~ (except possibly SN1987A in the LMC) in that it exhibits strong Ha emission in the early spectra, less than 10 days after it exploded. The spectra also show an ultraviolet deficit below the blackbody extrapolated from longer wavelengths. The light curves in V, R, and I dropped slowly during the first few months after detection, resembling a Type IT "plateau" supernova, and dropped precipitously near 200 days past maximum. We have also measured the wavelengths and velocities of the stronger emission and absorption features, with tentative identifications.