Forecasting weekly data

This is another situation where Fourier terms are useful for handling the seasonality. Not only is the seasonal period rather long, it is non-integer (averaging 365.²⁵⁄₇ = 52.18). So ARIMA and ETS models do not tend to give good results, even with a period of 52 as an approximation. Regression with ARIMA errors The simplest approach is a regression with ARIMA errors. Here is an example using weekly data on US finished motor gasoline products supplied (in thousands of barrels per day) from February 1991 to May …