For only the sixth time in 133 years of records, Adelaide, Melbourne and Sydney have all reached 30 degrees on the same day this late in the season.

As of 3pm AEDT on Thursday, the running maximum temperatures in these three capital cities was 32.5 degrees in Sydney, 32.3 degrees in Adelaide and 30.4 degrees in Melbourne.

While this type of warmth in each individual city is not uncommon in early autumn, it's more rare to see all three locations exceeding 30 degrees on the same day, this far into the season.

In records dating back to 1887, Adelaide, Melbourne and Sydney have only collectively exceeded 30 degrees 12 times during autumn. This includes today. This late in the season, which is on or after March 19th, this feat has only happened six times in 133 years, the last being on April 4th 1986.

Today's trio of thirties was made possible by a broad high pressure ridge over eastern Australia interacting with a low pressure system to the south of the country. These synoptic features allowed warm inland air to travel towards the nations eastern and southern coasts at the same time, with sufficient strength to hold out sea breezes in all three cities.

The latest date in autumn to see Melbourne, Adelaide and Sydney all reach 30 degrees was April 9th in 1969.