Many factors are affecting the fruit growth dynamics of fruit trees. The vapour pressure deficit (VPD), the measure of the drying power of the air, integrates temperature and air humidity data, is one of the crucial factors affecting this process. In the current study carried out in an apple orchard in southeastern France, fruit diameter and VPD values were recorded by a wireless sensor network. A regression model was created utilizing feed-forward learning and predicting algorithms. With the obtained model, the relationships between VPD and fruit growth can be computed. As an example, when we keep the humidity conditions constant and increase the temperature by 2 °C in the model, the fruit diameter decreases by 0.18%.