  We present a new spectrum of the quasar HS1603+3820 taken 1.28 years (0.36
years in the quasar rest frame) after a previous observation with Subaru+HDS.
The new spectrum enables us to search for time variability as an identifier of
intrinsic narrow absorption lines (NALs). This quasar shows a rich complex of C
IV NALs within 60,000 km/s of the emission redshift. Based on covering factor
analysis, Misawa et al. found that the C IV NAL system at z_abs= 2.42--2.45
(System A, at a shift velocity of v_sh = 8,300--10,600 km/s relative to the
quasar) was intrinsic to the quasar. With our new spectrum, we perform time
variability analysis as well as covering factor analysis to separate intrinsic
NALs from intervening NALs for 8 C IV systems. Only System A, which was
identified as an intrinsic system in the earlier paper by Misawa et al., shows
a strong variation in line strength (W_obs ~ 10.4A -> 19.1A). We speculate that
a broad absorption line (BAL) could be forming in this quasar. We illustrate
the plausibility of this suggestion with the help of a simulation. Under the
assumption that a change of ionization state causes the variability, a lower
limit can be placed on the electron density (n_e > 3x10^4 cm^-3) and an upper
limit on the distance from the continuum source (r < 6 kpc). On the other hand,
if the motion of clumpy gas causes the variability (a more likely scenario),
the crossing velocity and the distance from the continuum source are estimated
to be v_cross > 8,000 km/s and r < 3 pc. In this case, the absorber does not
intercept any flux from the broad emission line region, but only flux from the
UV continuum source. If we adopt the dynamical model of Murray et al., we can
obtain a much more strict constraint on the distance of the gas parcel from the
continuum source, r < 0.2 pc.
