For surfers, a great day on the water is dependent on the size of waves coming ashore. Most of the waves they catch are caused by wind transferring energy from the air to the water. The energy moving through the water causes the disturbance that is seen, felt, and sometimes heard, as a wave. The size of a wave depends on several factors. First, the strength of the wind affects wave formation. Stronger winds generally lead to larger waves. Second, the duration of the wind or how long it blows. The longer the wind blows consistently, the better chance that there will be higher wave heights. The third factor is the area of open sea over which wind can blow, known as fetch. Larger fetches tend to lead to larger waves.

A wave begins to break when it moves into shallow water where the depth is less than half its wavelength. The wave’s energy is now compressed into a smaller area of water, causing it to become steeper and eventually toppling over. In the ocean, there are two major types of breaking waves: plungers and spillers. When waves encounter a steeply sloped bottom, they crash violently, forming plungers. On more gently sloped coastlines, waves tend to pour over themselves, forming spillers. For surfers, riding a spiller provides a long, smooth ride but riding a plunger results in a fast and exciting, but often more dangerous ride.

To catch a wave, surfers typically paddle out from the beach through the breaking waves to the surf line. There, they wait for a good wave to rise beneath them. When they select the wave they want to ride they lay down on their boards and paddle with their hands until they catch the wave pop up onto their feet and ride the wave towards shore. Most surfers chase waves that range from three to six meters (nine to 20 feet) high. Big wave surfers, however, can catch waves more than 21 meters (70 feet tall). Big wave surfers often have jet skis or small boats tow them safely out past the breakers and into rising swell helping them catch high velocity waves. This technique is called tow surfing.

Modern technology and wave prediction has changed the sport of surfing allowing surfers to watch their computers to know when it is time to head to the beach for the best surf. Surfcasters, such as Sean Collins, take wind speed, wind duration, and fetch into consideration when they make predictions. They also consider geographic factors, the direction the beach faces, and interference from nearby islands or other landforms and the bathymetry or depth of the seafloor near possible surf sites. Features such as sandbars or reefs might cause predictable places where waves crash called surf breaks. Surfcasters use data from satellites and buoys near and off shore to examine wind and weather patterns. Computer models process data and make predictions about what future surfing conditions will be like days to weeks ahead of time.