Forecasting weekly data

What would you do if the seasonal period is rather long and non-integer? For example, if you have a weekly data, ARIMA models do not tend to give good results. The simplest approach in such situation 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 2005.

http://www.r-bloggers.com/forecasting-weekly-data/