With the northlerly wind component on Tue/Wed you'll love it at Quindalup (slightly east of Dunsborough). There's a sand break about 700m out which makes for shallow flat water between that and the beach.

If you're not familiar with the area it may be a little difficult spotting which carpark has the best beach, but if you get yourself about half way between Tulloh and Elmore streets along Geographe Bay Road you should be right. The carpark is gravel and trees shade the entire carpark area.