  The High Altitude Water Cherenkov (HAWC) Observatory monitors the gamma-ray
sky in the 100 GeV to 100 TeV energy range with > 95% uptime and unprecedented
sensitivity for a survey instrument. The HAWC Collaboration has implemented an
online flare monitor that detects episodes of rapid flaring activity from
extragalactic very high energy (VHE) sources in the declination band from -26
to 64 degrees. This allows timely alerts to be sent to multiwavelength
instruments without human intervention. The preliminary configuration of the
online flare monitor achieves sensitivity to flares of at least 1 hour duration
that attain an average flux of 10 times that of the Crab Nebula. While flares
of this magnitude are not common, several flares reaching the level of 10 Crab
have been observed in the VHE band within the past decade. With its survey
capabilities and high duty cycle, HAWC will expand the observational data set
on these particularly extreme flares. We characterize the sensitivity of the
online flare monitor and outline plans for its upcoming deployment.
