premise: Waves become swell when they leave the area of wind in which they were generated. Long after the wind that created it has stopped blowing, swell can continue to travel for thousands of miles and have a life span dependent on its wave length and the extent of ocean. The longer the wave the faster it travels and given sufficient sea room the longer it continues to travel. Wind can generate waves that travel faster than the wind itself and after a few hours of blowing the wave can be a long way ahead of the wind. At sea the arrival of a swell can be an indication of bad weather to come. If a long low swell arrives and it steadily increases in height then you should prepare for an approaching gale. If the swell remains long and low then it is likely that the wind that generated it is a long way away and you will escape it. Sometimes a swell generated far away crosses the waves generated by another wind. This can lead to a confused and in the extreme a dangerous sea state.
hypothesis: The sentence wind can generate waves that travel faster than the wind itself and after a few hours of blowing the wave can be a long way ahead of the wind would be more correct if it read Wind can generate waves that travel faster than the wind itself and after a few hours of blowing the swell can be a long way ahead of the wind.