Interaction of a shockwave with turbulence can generate large thermodynamic fluctuations in a flow. This can lead to enhanced mixing, peak heat transfer and high sound level. The canonical interaction of homogeneous isotropic turbulence with a nominally normal shock wave acts as a model problem to investigate physics and develop predictive models. The case of purely vortical turbulence upstream of the shock is arguably the most fundamental case and it is the focus of the current work. We use direct numerical simulation (DNS) data and linear interaction analysis (LIA) to develop a predictive model for the thermodynamic field. Specifically, transport equation-based models are proposed for the variances in temperature, pressure,density and entropy. The jump in the thermodynamic variances are modeled in terms of the mean compression at the shock,and the closure coefficients are obtained via Kovásznay mode decomposition. By comparison,the downstream decay is modeled in a phenomenological way in terms of acoustic transient near the shock and a far-field decay due to viscous dissipation. The model predictions are found to match well with available DNS data for a range of shock strengths. In addition,the closed-form solution of the model equations give the scaling of the thermodynamic fluctuations with mean flow Mach number.