Jan 5 - 16 is the 20th Summer Deafolympics. Approx 3,000 competitors from 90 countries.

Dec 27 - Jan 8th is the National and World Championships for Hobie and Moths. (Sailboat racing, if you will.) Competitors from 29 countries.
Part of Sail Melbourne regatta which draws salties from around the world most years - the normal regatta for Olympic and invited classes is one of only 5 ISAF Grade 1 events around the world each year and the only one in the Southern Hemisphere. Numbers for that have been boosted from the normal this year due to the above mentioned Worlds in those two classes.

Early Jan will be flat out with holidaying families from both sides of the Tasman without these sort of special events anyway.