tlcconsult,
I found that searching CPAN for "smoothing" turned up a number of results but that adding "winters" for instance turned up 0. Perhaps that means that none of them implement the specific algorithm you want but you might want to double check as CPAN search is far from perfect.

I did do a google code search and it implies that rrdtool has what you want (I didn't verify) or alternatively you could use the perl bindings to R and run it there.