Flash flooding (FF) in Vietnam has become an important issue due to increasing loss of property and life. This paper investigates FF prediction using the Kinematic Run-off and Erosion model to perform comprehensive analyses to: (1) evaluate the role of initial soil moisture (θ) conditions using the Bridging Event and Continuous Hydrological model; (2) model the discharge (Q) using different rainfall inputs; (3) test the sensitivities of the model to θ and Manning's n coefficient (N) on Q and validate the model; and (4) predict channel discharge (QC) using forecasted rainfall. A relative saturation index (R) of 0.46 and N of 0.14 produced the best match of the simulated outflow to measured Q, while the saturated hydraulic conductivity (Ksat) and R had significant effects on the magnitude of flooding. The parameter N had remarkable influences on the volume of flow and its peak time. Surprisingly, the use of radar rainfall data underestimated Q compared to the measured discharge and estimates using satellite rainfall. We conclude that the KINEROS2 model is well equipped to predict FF events in the study area and is therefore suitable as an early warning system when combined with weather forecasts. However, uncertainties grow when the forecasted period expands further into the future.