why are waves bigger during the winter?

Answer 1

Due to the weather patterns.
In the mid-atlantic where I'm from, waves are bigger in the winter like you said. The jet stream moves north in the summer, so low pressure systems tend to move off the coast north of NJ, MD etc and not producing the swells that occur with a low moving off the coast.
However in the winter, the jet moves to the south and low pressure systems tend to move off the coast and travel north bringing better swells and bigger waves to the mid-atlantic. Hardcore surfers where I'm from love to surf in the winter because of the bigger waves and the lack of the more inexperienced surfers (like me, haha).

I'm not sure where you're from but the situation may be similar.

Answer 2

The size of a wave depends on the wind speed and not on the season although large waves do form in high tides.

Answer 3

iono