We (Venice Area) are entering our winter weather pattern. While air temps can still get into low 80s, water temp has dropped significantly. O2 temp is in the mid 60's now, and went as low as mid 50s last winter. IMO the minimum wet suit for winter is 7mm with a hooded vest under. My dive buddies and I all have dry suits, and will dive dry when air and O2 temps are low. A semi dry suit would also serve well during the winter here, and is not as expensive and complicated as diving dry suit. We dive all year round, and find that winter is best for spearfishing. Hope this helps, I'm sure there may be other opinions, but as I said we dive all year round.
Capt. Dan Sansiveri