I found a wonderful image on BOM website (everyone has already probably found it) for sea temperatures for SEQ, which got me thinking. Wouldn't shallower costal waters be warmer than the deeper sea off of the continental shelf.
Is it colder night time temperatures of the land reducing the temperature of water near the land, or is it the current off shore are bringing warmer waters down and costal water appear to be coming up from the South.

Coastal temps are around 20 or 21 degrees, but further offshore it is 22.