To maximise energy conversion, real-time control of a Wave Energy Converter (WEC) requires knowledge of the present and future excitation force (Fex) acting on the device, which is a non-measurable quantity. The problem of estimation and forecasting of Fex becomes more challenging when arrays of WECs are considered, due to the hydrodynamic interactions in the array. In this paper, a global Fex estimator for a complete WEC array is developed and compared to a set of independent estimators which utilise information local only to each device. A significant question is whether the array of measurements is sufficient to compensate for the greater complexity of the wave field, compared to the isolated body case. The paper shows that the global estimator is always more accurate than the independent estimator, improving up to 45% the estimation accuracy of the independent estimator. Regarding prediction, two different Fex forecasters for a WEC array are compared: a global forecaster, utilising Fex estimates from the full set of array devices, and an independent forecaster, utilising only a local Fex estimate. We demonstrate that the global forecaster achieves more accurate results, not only compared to the independent forecaster, but also compared to the isolated body case.