A so-called "katabatic" wind occurs when cold, therefore dense, air drains down a slope. If the draining air gets squeezed between headlands, the wind generated can be quite sailable. Italy's Lake Garda is an extreme example of this.
I have found that the Clyde River at Bateman's Bay gets a regular katabatic wind. The critical triggers seem to be overnight frosts on the tablelands, and calm conditions at "the Bay".
To take advantage of this phenomenon, you have to be rigged and ready to sail not long after sun up. You can rig big; the wind probably will not exceed 15 knots. The wind will dissipate after about an hour; be prepared to wallow back to shore. The wind will be "offshore", so discretion is required. Early morning is shark feeding time; plenty of incentive to make those gybes! 
There are probably lots of places in southern Australia where katabatic winter winds occur. What is "unnatural" is to consider that there's local sailable wind to be had early in the morning, when, so often, the BOM forecast suggests nothing sailable for the entire day.
Good luck in your quest. 
I always thought Anabatic (spelling?) and Katabatic winds occured at dawn / dusk ?
I always thought it was like a reverse seabreeze in winter due to the early morning heat differential between the land and sea?
From BOM 'Land Breeze'
'A local offshore wind. At night, when the land cools more quickly, and to a greater extent, than the sea, the land breeze circulation is set up.
Cooler air from the land flows offshore to replace the warm air rising over the sea.
The air in contact with the sea warms and expands and the resulting changes in the pressure and temperature differences and distributions cause the land breeze circulation.'
Other references state that it can be any large body of water such as a lake etc.
We get these in Hobart regularly in winter, along with fog and mist coming down the Derwent river. Normally about 0-2 degrees and wind chill making it seem well under 0 degree. Wind ranges 12-20 knots, water is slightly choppy and my car and office heater is so much more appealing.
Katabatic wind, again from BOM
'Downslope wind caused by greater air density on the slope than at some distance, horizontally from it. The wind is associated with surface cooling of the slope.'
Dont like my chances of sailing down a slope.
