Darwin just had its hottest September day on record and its hottest day for any month in two years.

A surge of southeasterly winds carrying warm inland air across the western Top End caused temperatures to soar in Darwin on Tuesday.

This burst of abnormal Top End heat was caused by the same large high pressure system that’s currently driving a mass of polar, snow-bearing air across southeastern Australia.

The weather station at Darwin Airport reached 38.0ºC at 1:46pm on Tuesday, which beat its previous September record of 37.7ºC from 1983. This site has records dating back to 1941.

Another weather station at Darwin Post Office, which operated between 1869 and 1962, recorded 38.3ºC in 1892. However, it is well documented that temperature observations taken prior to 1910 are prone to error. Why? Because the instruments used to observe temperature in Australia were not standardised until the early 1900s.

The graph below shows how many months per decade contained temperatures in the top five percent of historical records at Darwin Post Office. As you can see, there were far more in the period prior to 1910.

Darwin Airport’s highest temperature on record was 38.9ºC in October 1982. This is also higher than any temperature reliably measured at the old Darwin Post Office site after 1910. The highest pre-1910 temperature was 40.4ºC in October 1892.