Hi Stylez,
Most experienced riders ride year round, well almost anyway. May and June are usually windless and epic for surfing so there's no reason to kite then anyways.
Winter time is for the experienced riders who are used to difficult conditions generally, there are some nice days occassionally but it is normally very gusty, strong and squally with wind speeds ranging from 15 to 40 knots in rain squalls.
Winter winds tend to be W/NW which is the opposite to our normal sea breeze and the winds are frontal not convectional. There is usually a fair amount of swell associated with the big days.
it's still rideable, you just need to know what you are doing and play it very carefully, especially when you see a rain cloud approaching. Either land your kite very quickly or get way out away from the beach until it passes.
It is highly recommended to fly kites with massive depower and good stability in such conditions so you don't become a statistic.
Good winds,
