  We investigate the primordial scalar perturbations in the thermal dissipative
inflation where the radiation component (thermal bath) persists and the density
fluctuations are thermally originated. The perturbation generated in this model
is hybrid, i.e. it consists of both adiabatic and isocurvature components. We
calculate the fractional power ratio ($S$) and the correlation coefficient
($\cos\Delta$) between the adiabatic and the isocurvature perturbations at the
commencing of the radiation regime. Since the adiabatic/isocurvature
decomposition of hybrid perturbations generally is gauge-dependent at
super-horizon scales when there is substantial energy exchange between the
inflaton and the thermal bath, we carefully perform a proper decomposition of
the perturbations. We find that the adiabatic and the isocurvature
perturbations are correlated, even though the fluctuations of the radiation
component is considered uncorrelated with that of the inflaton. We also show
that both $S$ and $\cos \Delta$ depend mainly on the ratio between the
dissipation coefficient $\Gamma$ and the Hubble parameter $H$ during inflation.
The correlation is positive ($\cos\Delta > 0$) for strong dissipation cases
where $\Gamma/H >0.2$, and is negative for weak dissipation instances where
$\Gamma/H <0.2$. Moreover, $S$ and $\cos \Delta$ in this model are not
independent of each other. The predicted relation between $S$ and $\cos\Delta$
is consistent with the WMAP observation. Other testable predictions are also
discussed.
