Dear old Bureau of Meteorology up to usual tricks claiming a hottest evah record hot night for Sydney but ignoring the UHI. The record is not worth the paper it is printed on due to the huge urban heat island UHI.
Sydney weather: Overnight temperature is record high for December, BOM says 
AWN lets you look around the region and see that the night of the 14th was warmest in the Sydney core stations, Obs Hill 27.1, Airport 27.5, Parramatta 27.5. Note RICHMOND RAAF (067105) at 23.6 further west in the UHI – the record there for Dec is 25 in 2000. The earlier RICHMOND RAAF (067033) 1928-1994 has 25.5 in 1990 as the record Dec night. All pointing to this warm night event being nothing special – unless you want to beat up global warming.
From a population of less than 200,000 in 1868 to one of near 5,000,000 in 2016, now that really is some elephant!
An open screen method of recording temperature could have been used back in 1868? However this seems unlikely to have influenced the accuracy of the minimum reading significantly compared with what a regulation Stevenson screen measurement would have shown.
www.john-daly.com/screens.htm
The jacaranda trees in Adelaide streets are blooming well, a better show than most years yet they are 3-4 weeks later than usual. The two explanations for the delay are that they had to wait until the ground warmed up or that the delay was due to a dry Spring. The Spring was NOT dry (nor the Winter with precipitation setting records) but guess Who believes the second?
On a minor matter I notice that in the Adelaide Hills the agapanthus are flowering late for the second year running. Mine at the front of the garden bed (sloping down to the road) are flowering while those at the top of the garden are just sending up stalks, despite also being in full sun. Similar to last year when top ones flowered Dec.22/23, 3 weeks after the others. I notice that this seems general with plants on the verge of the roads around the Hills all flowering including some with limited sunshine whilst those set back are not flowering. Must be due to AGW.
Graeme here in central Victoria our blue pacific bush normally flowers on 21 to 23 September regular as clockwork but this year it flowered a good three weeks later. Not lack of water, we’ve had a very wet spring, the September rainfall was the highest on record for local short data record stations Castlemaine and Vaughan. Even Newstead with rainfall data going back more than 100 years showed this September to be the wettest since 1916.
So the cooler weather and lower ground temperatures are my bet.
The Perth flowering of Jacarandas was later too. I was down there 3 weeks ago, and had to ask, is this August winter weather, it sure felt like it.