Fire whirls cause strong wind damage in large outdoor fires such as wildland fires and urban fires. A model to predict the maximum tangential wind velocity in laboratory-scale fire whirls without flames in a crosswind is developed based on a generation mechanism and the properties of the fire whirls. The model also predicts the radii of the fire whirls and the crosswind speed when they occur. The fire whirls modeled are those with large circulation and large radii, that is, large intense fire whirls. These fire whirls occur and remain downwind of a fire line placed perpendicular to the crosswind under a low crosswind speed and a high heat release rate (HRR). The model agrees well with the experimental results.