Where do the Waves Come From?

Following the biggest summer swell in years (for SoCal) the waves backed down to chest high then knee high then less. Today and tomorrow we are expecting a little SW swell. Emphasis on little because the storm that spawned this swell was off New Zealand and had a track direction that will rob our area of some of the swell energy (angular spreading decay).

Where do the waves come from? Short answer, the Sun. Earth receives more heat along the equator than at the poles. Hot air rises and cold air sinks. The rising hot air has lower pressure and we call those areas "Lows" and vice versa. This would make for some very boring weather but Earth is tilted and it spins. The spin of the Earth separates the global circulation into bands such as the Tropical Easterlies (wind from the East) and the Mid Latitude Westerlies which cover the 48 states as well as Europe. From the interactions of cold air, warm air, moist air, and dry air we get storms. For a storm to produce surf, it needs some staying power so we normally look to big low pressure systems in the far North (winter) or South (summer). We also can get great surf from tropical systems (hurricanes, typhoons, cyclones). For a great explanation of how the winds from these storms become good surf, read Sean Collins explanation on Surfline:
So how do we get Surf?

For a book which goes much deeper into the science behind forecasting waves:
Wetsand Wavecast Guide to Surf Forecasting by Nathan Cool

Meteorology Today linked in the Amazon box on the right is great!
If you want to know more about all types of weather, this is the best textbook I ever used in any subject. My edition is about 15 years old, so hopefully it only got better. And a used copy might be much cheaper. Easy to understand explanations of every weather phenomena.