Determination of the time history of water temperature in an estuary is accomplished by using a thermal quality model in conjunction with a hydrodynamic simulation model. The hydrodynamic model computes tidal stages and flows throughout the estuary for any tidal cycle. The thermal quality model uses the results of the hydrodynamic model and observed meteorologic data to predict water temperatures. These models have been used successfully in case studies to reproduce observed water temperatures. The sensitivity of the resulting temperatures to the various meteorologic parameters, such as wind conditions, dew point temperature, and solar radiation, is presented. Dew point temperature is shown to exert a major influence on water temperature.