waves generated by local wind - if this wind is persistent over deep water then these sea waves may become swell waves
newly formed seas are very chaotic & disorganised, resulting in choppy conditions
as the waves begin to grow, the windward wave surface becomes steeper & steeper until the wave height approaches approx. 1/7th of the wavelength, once the steepness reaches 1:7, the wave usually breaks, forming whitecaps & spray.
waves merge, overtake each other, cancel each other out, until equilibrium occurs when energy received approximates energy lost resulting in “a fully developed sea” - the time required and the fetch required (distance wind is exposed to the water) to achieve this state increases with wind speed.
sea waves usually travel slower than the wind generating them due to “slippage” between the wind and water - usually 1:20 sloping chop moves at ~20% of the wind speed increasing to 50% of wind speed in a fully developed sea with 1:10 steepness.
as the sea waves continue to develop, they tend to fan out from the storm area, thus their energy dissipates & gradually forming lower, longer and more rounded swell waves with perhaps 1:50 slope (see below) from distances in tens of km and more (and usually more than 1 day's travel) from the storm centre.
indicative fully developed seas for various winds over deep water:
Beaufort 3 “gentle breeze” of 19kph or 10knots will produce a 0.5m wave in about 6hrs, reaching peak average wave height of 0.8m by 24hrs
Beaufort 4 wind averaging 20-28kph or 11-16knots blowing over a fetch of at least 24km for at least 4.8hrs will result in a peak average wave height of 0.6m with wave period of 3.9sec and wavelength of 16m.
Beaufort 6 “strong wind” averaging 39-49kph or 22-27knots blowing over a fetch of at least 140km for at least 15hrs will result in a peak average wave height of 2.5m with wave period of 7sec and wavelength of 51m.
a near gale of 30knots will produce a 2m high wave in less than 4hrs, building to 3m by 8hrs, 4m by 16hrs, 5m by 35hrs & reaching peak average height of 6.5m by about 200hrs or more.
a gale (Beaufort 8) will produce 2m high waves in less than 2hrs, 3m by 4hrs, 5m by 10hrs, 8m in 35hrs and potentially up to 12m
shallow water:
when waves reach shallower waters where depth is less than half the wavelength of the wave, friction against the sea bottom can cause them to grow in height & become steep-sided resulting in “short seas”. More worrying for boaters is if the water depth is less than 80% of the height of the wave, the wave will tend to break, thus a 2m groundswell could become a 3-4m high steep-sided 'breaker'. Bass Strait is generally less than 60m deep & some of the waves generated by storms in the Southern Ocean can grow to a menacing height as they encounter these waters.
shallow water waves are also influenced by:
reflection - waves reflecting back from rocky cliff or sea wall resulting in steep sided bumpy waves that don't go anywhere - “standing waves” which can fool sailboarders into thinking there is more wind than there really is.
diffraction - waves diffract around a barrier such as an island or breakwater
refraction - waves in shallowest water move the slowest resulting in the wave front bending to become approx. parallel with the underwater contours.
waves generated in shallow waters:
for water depths > 1.5m, depth does not significantly effect wave height if fetch is < 1km and wind speed < 35knots, but the greater the fetch, the more the effect water depth has on maximum possible wave height produced for a given wind speed, such that for 15knot winds with fetch of 500km, wave height will rise from 0.3m in 1.5m deep water to 1.1m in 15m deep water.
likewise for 35knot wind over 500m fetch, wave height will rise from 0.5m in 1.5m water to 2.6m in 15m water depth.
NB. tides behave as shallow water waves even in deep oceans as their wavelength (half of earth's circumference) is greater than 20x ocean depth.