  We measure wind velocities on opposite sides of the hot Jupiter HD$\,$189733b
by modeling sodium absorption in high-resolution HARPS transmission spectra.
Our model implicitly accounts for the Rossiter-McLaughlin effect, which we show
can explain the high wind velocities suggested by previous studies. Our results
reveal a strong eastward motion of the atmosphere of HD$\,$189733b, with a
redshift of $2.3^{+1.3}_{-1.5}$$\,$km$\,$s$^{-1}$ on the leading limb of the
planet and a blueshift of $5.3^{+1.0}_{-1.4}$$\,$km$\,$s$^{-1}$ on the trailing
limb. These velocities can be understood as a combination of tidally locked
planetary rotation and an eastward equatorial jet; closely matching the
predictions of atmospheric circulation models. Our results show that the sodium
absorption of HD$\,$189733b is intrinsically velocity broadened and so previous
studies of the average transmission spectrum are likely to have overestimated
the role of pressure and thermal broadening.
