  The CDF II experiment has recently determined the mass of the $W$ boson to be
$m_W(\text{CDF II}) = 80.4335 \pm 0.0094~$GeV, which deviates from the standard
model prediction at $7\sigma$ level. Although this new result is in tension
with other experiments such as those at LHC and LEP, it is worth discussing
possible implications on new physics by this anomaly. We show that this large
discrepancy can be explained by non-aligned vacuum expectation values of
isospin triplet scalar fields in the Georgi-Machacek model extended with
custodial symmetry breaking terms in the potential. The latter is required to
avoid an undesirable Nambu-Goldstone boson as well as to be consistent
treatment of radiative corrections. With $m_W(\text{CDF II})$ as one of the
renormalization inputs at the 1-loop level, we derive the required difference
in the triplet vacuum expectation values, followed by a discussion of
phenomenological consequences in the scenario.
