HOW FAST DO WAVES TRAVEL?
Swells and the individual waves within a swell travel at different speeds. For the swell to keep moving forward, individual waves are constantly rotating positions. Fast waves catch up with slower waves & slower waves are caught up by faster waves in a continuous conveyor belt.
Swell speed is measured at nautical miles per hour or knots. (1 knot is 1.2 miles on land.)
In order to work out the speed that a swell is travelling multiply the wave period by 1.5. The result is the speed the swell is travelling in knots.
To work out how fast individual waves are travelling multiply the wave period by 3.
WHAT IS WAVE DECAY?
Wave decay refers to the energy loss within a swell as waves propagate outwards from where they were generated. The further the distance travelled the more energy is lost and is dissipated.
A quote from Willie Wong’s blog ‘Bubbles Bad, ripples Good’ he states
“dispersion is the tendency for the wave to occupy more and more area as it propagates.”
HOW ACCURATE ARE SURF FORECASTING WEBSITES?
Surf forecasting websites have become very accurate over the past 10 years. The introduction of nearshore swell models, the ease of gathering meteorological information and the freedom of data provided by NOAA has allowed surf forecasting sites to provide detailed relative information for surfers. Combined and developed with local impressions surf forecasting websites are at the forefront of surfing.
However, the caveat remains that understanding and interpreting the data provided is a personal expectation that needs managing.
WHAT IS SHOALING?
Shoaling is the name given to how a waveforms and breaks.
As waves reach the shallow water of the coastline the wave runs out of space. Think of the wave as a recirculating sphere that rotates towards the shore, as the seabed becomes gradually steeper and the depth of water decreases more of the waves energy is forced upwards towards the surface, gradually increasing the height of the wave.
Waves with a longer period have more energy and so more water is forced upwards creating a larger wave.
3ft @ 10seconds = 2-3ft wave with not much power
3ft wave @ 16 seconds = a much larger and more powerful 4-5ft wave
Waves will start to break in water 1/3rd the height of the wave. 3ft wave will break in 5ft of water. The topography of the seabed will affect how quickly a wave will form and how it will be break.
Waves that travel from the deep ocean and reach a sharp incline will form quickly and break fast.
Waves that travel on a gentle incline will form slowly and crumble.
WHAT ARE WAVE BUOYS, HOW DO THEY WORK?
Wave buoys give surf forecasters a real time idea of what is happening out at sea. Contrary to common beliefs wave buoys do not provide much information for day to day surf reports.
The majority of the data needed for surf forecasting comes from a variety of meteorological weather stations, satellites and historical data, enabling a forecast or advanced picture of what can be expected to be produced.