You can get away without a wetsuit ( I had my firts wetsuitless session of the season on Sunday ) .... But the wind can cause havoc if we get a southerly or sw it is usually quite cold and can feel like it is warmer in the water than in the wind..... If you have a wetsuit top it may be worth throwing that in just to keep the wind off the wet skin.
Bay temp is about 21 deg.
earthsci.unimelb.edu.au/engage/dynamic-earth-updates/bay-windsthat link is a good one for winds and direction in the bay.
Enjoy your stay