As said the sea breeze is caused by thermal effects. basically as warm air rises over the land, cooler air is sucked in off the water. We get easterlies in summer because the center of the high pressure cells are below Australia (High pressure cells rotate anti clockwise) hence the easterly.
The high pressure cells are moving north and aren't dominating as they do in summer so we are being effected now by weather below them and above them. As the high moves across Australia a trough forms down through the middle of it along the coast which sucks down all the moist air from the north. Of course the suns going north as well so thermal effects are reduced.
soon the high pressure cells will be far enough north to allow cold fronts to sweep up from underneath. winter!!! Time to drive north back up to the top of the high pressure cells.
Thats why Geraldton is so windy this time of year. We'll save gradients for another day.