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Guide to wind generated waves

There are many factors that determine the size and ride-ability of a wave. In this guide to wind generated waves we will try to give you a basic understanding of the processes which go into riding the waves we love. The waves that we like to surf are generated by wind. The wind blows on the surface of the sea and this creates ripples and waves depending on the strength of the wind. On a weather map these offshore storms are indicated as low pressure areas. The more tightly the isobars the stronger the wind.

Here are other factors that should be taken into account when forecasting waves for surfing:

weather map with isobars

Weather map with isobars    Photo by Kit

1 SPEED

The stronger the wind blows, the larger the ripples and waves become. Initially they will be small but with increasing wind speed they will gradually increase in size.

2 DURATION

The longer the wind blows, the bigger the waves. The wind gets hold of the smaller waves and they increase in size.

3 FETCH

The official definition of fetch is: “An ocean area where waves are generated by a wind having a constant direction and speed”. A large storm with wind blowing in the same direction will therefore generate bigger waves than a tiny local storm.

4 PERIOD

A wave has two parts: The top of the wave is know as the crest, the bottom is called the trough. The wave period is defined as the time between two successive crests. Long period waves tend to be stronger and larger while shorter period waves are less energetic and more messy. Generally longer period waves travel longer distances, create higher breakers and are much more favored by surfers.

5 WIND SWELL

Wind swell is considered a short period swell, usually under 11 seconds. These are generated by wind close to the shore. They do not travel long distances and do not carry deep energy within them.

6 GROUND SWELL

Longer period swell usually between 12 -25 seconds. The waves travel longer distances but they are maintaining a lot of energy. They are no longer being affected by the winds that generated them. As it approaches all the energy is being projected on the ocean floor, that is why it is called ground swell.

Onshore wind generated waves

Onshore wind    Photo by J.Kleeman

7 ONSHORE

Wind blowing in from the sea onto the shore are called onshore winds. They are the worst for surfing. Depending on the strength of the wind the waves become unsurfable and messy.

8 OFFSHORE

Wind blowing from the shore into the sea are called offshore winds. They are the best for surfing. The waves are well formed and break perfectly. A solid ground swell combined with offshore winds are the best surfing conditions.

9 SIDESHORE

Not desirable wind for surfers either. Not as perfect as offshore but better than onshore. The waves start to form and are surfable.

However for a good surf session you need more than just wind and waves. Swell direction, sea floor features and tides also affect the size and ride-ability of waves. Read our next article on how waves break here.

Featured image by NASA