There are loads of articles on the net covering this subject. If you want a really in-depth approach try this article
. What I'm going to do here is try to keep it short and simple and give you enough information to help make more accurate surf forecasts from the data we provide.
What creates waves?
Wind makes waves. Friction caused when wind blows over a flat sea will create waves. The more energy the wind imparts the bigger and more powerful the waves.
How can I tell how much swell will be generated?
The key words in judging the amount of wave energy a wind system is likely to produce are strength, fetch and duration.
- Strength - Pretty obvious. The faster the wind is blowing the more energy it will impart. On the wind forecast model this is colour coded. On an isobar chart closely packed isobars indicate stronger winds.
- Fetch - This is simply the area of ocean the wind is blowing over. A small, localised storm may only be tens of miles across, whereas a large storm system may cover hundreds of miles of open ocean. The greater the area of wind blowing in the same direction the more energy imparted and the bigger waves created. The situation is a little more complicated when virtual fetch is factored in. Imagine a large storm covering a thousand miles of ocean. Now imagine a smaller storm with a hundred mile radius tracking north at the same speed as the waves it created. North swells generated by this system would spend a longer time under its effect and the net result could be similar to the larger storm.
- Duration - The longer the wind blows over the same spot the bigger the swells.
So big storms mean great waves?
Not exactly. Ever been to the beach in the middle of a howling onshore? 10ft waves but you're not about to paddle out and have a great time. As waves travel away from a generating storm an important cleansing process takes place. Low period waves (the poor lumpy surf we all hate) quickly die away. Longer period waves have more energy and will continue to travel for a long time after leaving the storm. Whats more as these waves travel they join up with other waves with the same period. These groups of 2-8 waves travel more efficiently together and are the 'sets' that arrive on the beach.
What we want is large, powerful storms that send high energy swells towards our shores from a great distance! Simple really.