Surf forecasting is the process of using offshore swell data to predict onshore wave conditions.
Although both are present at most surf spots, groundswell creates much better breaking waves and dominates the lineup.
If there is a swell of significant height that is headed in the direction of the break you are forecasting for, then there probably will be good surf.
[2] Using swell data, which is readily available on the internet, it is possible to predict how the surf will be for a fairly large area.
Professional and advanced surfers tend to write surf logs or journals to document environment specific parameters such as wave size, tide height to learn and remember spot specifics and notable surf sessions.
In general there are gradual sloping ocean floors which result in a slower crumpling wave (better for long boarding) and steeper sloping floors which result in a faster, hollower breaking wave (better for short boarding).
Tides, which occur from varying gravitational forces between the Sun, Moon, and the Earth, are easy to predict far in advance.
Other surf breaks may experience the opposite effect and have better wave shape during high tide.
The National Weather Service in Honolulu, Hawai'i, publishes surf forecasts for O'ahu.