Wildfires often exhibit complex and dynamic behaviour arising from interactions between the fire and surrounding environment that can create a rapid fire advance and result in loss of containment and critical fire safety concerns. A series of laboratory experiments involving the interaction of two parallel fire lines on a uniform fuel bed without slope under the influence of wind is presented and discussed. The two fire lines are initially separated by a certain distance (1, 2 m) and the subsequent fire spread is described. The results show that the pyroconvective interaction between the two fire lines and ambient wind modified the rate of spread of the approaching fire lines and their associated spread characteristics, independently of the distance between them. A physical interpretation of fire evolution based on the dynamic interaction between two parallel fire lines under wind flow is proposed. We use a dimensionless physical parameter, the Froude number. The results also demonstrated the existence of a wind flow velocity between 1 and 2 m s−1, corresponding to a Froude number between 0.2 and 0.4 for which the rate of approach of the two merging fire lines is a minimum.