  A large drift in the rotation rate of Titan observed by Cassini provided the
first evidence of a subsurface ocean isolating the massive core from the icy
crust. Seasonal exchange of angular momentum between the surface and atmosphere
accounts for the magnitude of the effect, but observations lag the expected
signal by a few years. We argue that this time lag is due to the presence of an
active methane weather cycle in the atmosphere. An analytic model of the
seasonal cycle of atmospheric angular momentum is developed and compared with
time-dependent simulations of Titan's atmosphere with and without methane
thermodynamics. The disappearance of clouds at the summer pole suggests the
drift rate has already switched direction, signaling the change in season from
solstice to equinox.
