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In our last article we looked at the creation of waves in the North Atlantic by low-pressure systems. Today we will consider what happens as the waves approach our shores.

Now that the waves have been created (the swell) they keep on travelling across the ocean until they reach land and the wave energy is released in the form of breaking waves on the beach or cliffs

The further the swell travels from the weather system that created it, the more the waves spread out. This time between each crest is called the ‘wave period’. That is; the time taken for each wave to reach the same point as the last wave. For example if you are sitting on your surfboard out back you can easily count the seconds between each wave passing under your board. Those seconds translate into the wave period.

Swell that has travelled away from the weather system that created it is usually termed ‘ground swell’ and will have a wave period in the range of 10 – 20 seconds. A swell that has travelled for just 2 or 3 days would have a wave period of around 10 – 14 seconds. Swell that has travelled for up to a week could have a period of 16 – 20+ seconds. Obviously the longer the wave period the better for surfing!

Swell will travel approximately 250-300 miles per day, but there are weather factors that will have affects on swell as it travels. For example strong cross winds, that is; winds blowing across the wave, can destroy a ground swell as can strong head winds; winds blowing head-on into the wave. Strong head winds can drastically reduce the swell size.

Swell generally travels across the ocean best with calm weather conditions. These conditions are usually associated with large areas of high pressure. With the right conditions, perfectly lined up ground swell will arrive, and if your local beach has no wind or light off-shore winds (more on this later) when this ground swell turns up, the waves should be perfectly shaped. Surfing bliss!