1. Decompose the smooth curves via a functional principal component analysis.2. Fit a multivariate time-series model to each of the principal component scores.
3. Forecast the principal component scores using the fitted multivariate time-series models.
4. Multiply the forecast principal component scores by fixed principal components to obtain forecasts of $f_{n+h}(x)$.
5. Prediction intervals are constructed by taking quantiles of the one-step-ahead forecast errors.