  With its unprecedented sensitivity and spatial resolution, the James Webb
Space Telescope (JWST) has opened a new window for time-domain discoveries in
the infrared. Here we report observations in the only field that has received
four epochs (spanning 126 days) of JWST NIRCam observations in Cycle 1. This
field is towards MACS J0416.1-2403, which is a rich galaxy cluster at redshift
z=0.4 and is one of the Hubble Frontier Fields. We have discovered 14
transients from these data. Twelve of these transients happened in three
galaxies (with z=0.94, 1.01, and 2.091) crossing a lensing caustic of the
cluster,and these transients are highly magnified by gravitational lensing.
These 12 transients are likely of similar nature to those previously reported
based on the Hubble Space Telescope (HST) data in this field, i.e., individual
stars in the highly magnified arcs. However, these twelve could not have been
found by HST because they are too red and too faint. The other two transients
are associated with background galaxies (z=2.205 and 0.7093) that are only
moderately magnified, and they are likely supernovae. They indicate a
de-magnified supernova surface density, when monitored at a time cadence of a
few months to a ~3--4 micron survey limit of AB ~ 28.5 mag, of ~0.5 per sq.
arcmin integrated to z ~ 2. This survey depth is beyond the capability of HST
but can be easily reached by JWST.
