A number of heat-related records were broken in Sydney this month as the city experienced September-like days during the middle of winter.

July is typically Sydney's coldest month of the year, with a long-term average maximum temperature of just 16.4 degrees. This month, however, the average maximum temperature was 19.8 degrees, a whopping 3.4 degrees above average and breaking the previous July record of 19.5 from 2013.

Sydney's mean maximum temperature during July was even higher than a typical August (17.9C), and nearly as warm as an average September (20.1C). This July has also been warmer than the last four Augusts based on maximums.

In addition to the record-breaking average maximum temperature, Sydney also registered an unprecedented 13 days above 20 degree this month. This trumped the old record of 12 days from 2013.

Prior to 2018, July had always featured at least three days that were cooler than the current monthly average of 16.4 degrees. This year, there was only one - a near-average 16.2 degrees on Wednesday 11th.

The hottest day at Observatory Hill this month was 25.2 degrees on the 5th. This was the city's hottest day on record this early in July, although it fell short of Sydney's hottest July day, 26.5 degrees form 2017.

One of the main drivers behind Sydney's unseasonable daytime warmth this month was a lack of cloud and rain. The city experienced close to nine hours of sunshine per day on average, more than two hours longer than usual.

July's mean minimum temperature was a near-average 8.4 degrees in Sydney, with clear skies promoting overnight cooling. A notable standout was the minimum of 4.6 degrees on Monday 16th, the city's lowest July temperature in 11 years.

Two days of rain amounted to just 11.2mm during the month, making it Sydney's driest July in 23 years and ranking in the lowest 10 per cent of historical records.