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We present observations of SN 2020fqv, a Virgo-cluster Type II core-collapsesupernova (CCSN) with a high temporal resolution light curve from theTransiting Exoplanet Survey Satellite (TESS) covering the time of explosion;ultraviolet (UV) spectroscopy from the Hubble Space Telescope (HST) starting3.3 days post-explosion; ground-based spectroscopic observations starting1.1~days post-explosion; along with extensive photometric observations. Massivestars have complicated mass-loss histories leading up to their death as CCSNe,creating circumstellar medium (CSM) with which the SNe interact. Observationsduring the first few days post-explosion can provide important informationabout the mass-loss rate during the late stages of stellar evolution. Modelfits to the quasi-bolometric light curve of SN 2020fqv reveal ~0.23 $M_{\odot}$of CSM confined within ~1450 $R_{\odot}$ ($10^{14}$ cm) from its progenitorstar. Early spectra (<4 days post-explosion), both from HST and ground-basedobservatories, show emission features from high-ionization metal species fromthe outer, optically thin part of this CSM. We find that the CSM is consistentwith an eruption caused by the injection of $\sim$$5\times 10^{46}$ erg intothe stellar envelope $\sim$300 days pre-explosion, potentially from a nuclearburning instability at the onset of oxygen burning. Light-curve fitting,nebular spectroscopy, and pre-explosion \textit{HST} imaging consistently pointto a red supergiant (RSG) progenitor with $M_{\rm ZAMS}$$\approx$$13.5$--$15 \,M_{\odot}$, typical for SN~II progenitor stars. This finding demonstrates thata typical RSG, like the progenitor of SN 2020fqv, has a complicated mass-losshistory immediately before core collapse.

Progenitor and Close-In Circumstellar Medium of Type II Supernova 2020fqv from High-Cadence Photometry and Ultra-Rapid UV Spectroscopy