Swell is the collective term used to describe the long-period ocean waves that are generated by wind and other atmospheric forces. Swell 1 and Swell 2 refer to the two primary types of swell that are typically observed in coastal regions.
Swell 1 refers to the primary swell, which is typically the largest and most dominant of the two. It is characterized by a longer period (the time between successive wave crests) and a higher wave height (the distance from the crest of the wave to the trough) than Swell 2.
Swell 2, also called secondary swell, is typically smaller and less dominant than Swell 1. It is characterized by a shorter period and a lower wave height than Swell 1. It can be caused by a separate source of wind or weather system from the primary swell, or it can be the reflection of swell1 from a distant coast line.
When interpreting swell reports, you will generally be provided with information such as the swell height, the swell period, and the swell direction. Understanding this information, a surfer will decide which wave is the most suitable to surf, as they vary in size, direction and power.