Surfing - East coasts also receive heavy winter swells when low pressure cells form in the sub-tropics, where their movement is inhibited by slow moving highs. These lows produce a shorter fetch than polar fronts, however they can still generate heavy swells, since their slower movement increases the duration of a particular wind direction. After all, the variables of fetch and duration both influence how long the wind acts over a wave as it travels, since a wave reaching the end of a fetch is effectively the same as the wind dying off.