swell :: n.3 - A long wave on water that moves continuously without breaking.
forecast :: v.1 - To calculate or estimate something in advance; predict the future.
Surfers today are lucky enough to have technology on their side. With the advent of the internet and every increasingly easy access to live satellite imagery, weather satellite data, buoy data, and literally hundreds of weather stations in almost any given area knowing when and where the swell is going to be has gone from what used to seem like a black art to something manageable by anyone who can read and willing to spend a few minutes looking.
Swell forecasting is by no means 100% accurate but it's not far off most of the time and continues to improve as our understanding of how to interpret and analyze our available datasets becomes more refined.
Surfing Santa Cruz has aggregated what we consider to be the best sets of swell information into one easy to access source.
There are certainly other resources available but most are someones interpretation of the data. Rather than give you someone else's opinion on this we encourage you to utilize the information available to you to form your own opinions.