Sydney is on track to register its hottest year on record based on maximum temperatures.

The average maximum temperature at Sydney's Observatory Hill during the first 11 months of 2019 was 23.8 degrees. This was 2.4 degrees above the long term average and the highest on record for this period.

This month, the city's average maximum temperature during the first 29 days of December was 26.5 degrees. Based on forecast tops of 28 and 33 degrees for the final two days of the month, Sydney's average maximum temperature for December should come out at around 26.8 degrees.

While this won't be enough to challenge Sydney's December record of 28.6 degrees from 2005 and 1990, it should push the city's average maximum temperature for the year to about 24.0 degrees. This would be the first time Sydney's average annual maximum temperature has exceeded 24 degrees in 160 years of records.

Prior to 2019, Sydney's hottest year based on maximum temperature was 23.8 degrees in 2016, followed by 23.7 degrees in 2017 and 2013. The long-term average annual maximum temperature for Sydney is 21.8 degrees.

If Tuesday reaches its forecast top of 33 degrees, this will be Sydney's hottest New Years Eve since 34.0 degrees 1985.

Sydey's five warmest years on record based on maximum temperature have all occurred this decade.