What is the difference between the three swell maps?
The seastate that you can observe in a given place, is a mix of different type of waves:
The windsea (also called wind waves) is produced by the local wind.
The main swell is produced by a strong wind in a remote place. The swell travels great distances to where you observe it.
Secondary swells are produced also by winds in other remote places.
All of them have different heights, come from different directions and show different periods (i.e. the time between 2 wave crests)
Swell 1 is the main swell,
Swell 2 and 3 are secondary swells
The swell classification 1, 2, 3 depends on their respective heights
You find this detail on Windy by pressing the amber arrow on the picker.