The aim of this paper is to analyse the long term movements and, particularly, the seasonal pattern of Tenerife (Canary Islands) tomato exports throughout the last two decades. In order to observe more clearly the exporter's decisions, weekly data has been used. The instabilities in the long term behaviour of the series and the specific nature of the seasonal pattern should be taken into account in order to capture the performance of exports accurately. Thus, this analysis is carried out inside the frame delimited by the structural approach to time series and the usefulness of evolving splines as a tool capable of modelling seasonal variations in which either the period or the magnitude of the fluctuations do not remain the same over time is shown.