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A simplified analytical model was used to solve the salinity balance equation and study the relative contributions of freshwater flux and salt advection to the salinity tendency between the Gulf of Tehuantepec and Cabo Corrientes (14‐22°N). The model used climatological mixed‐layer salinity, satellite‐derived geostrophic velocity and evaporation minus precipitation data in a four‐domain scheme. The mean circulation derived from the model largely coincides with previous reports and suggests that, in the steady state, the Mexican Coastal Current (MCC) is decoupled from the Tehuantepec region. The analysis of the time‐dependent variability showed that the salt advection can be largely explained by the annual variations of the alongshore velocity (corresponding with the MCC) and an average salinity. At the seasonal scale, the salt advection and the freshwater flux have similar contributions to the resulting salinity tendency. Near Tehuantepec, due to a local salinity regime, the analytical model does not represent well the observations, while in Manzanillo and Zihuatanejo the agreement between the model and the observations is good in both amplitude and phase. The accuracy of the model in representing the observations is improved in the first third of the year by inclusion of the semiannual scale and the nonlinear processes in the equation of salt advection.