As most of southern Australia sweats under a prolonged heatwave, Sydney is on the verge of recording its longest spell of days below 30 degrees Celsius in 140 years.
While the weather has definitely at least resembled a version of summer since the pre-Christmas record cold spell, Tuesday's maximum of 26.6 degrees at Observatory Hill marked the 323rd consecutive day under 30C, already the longest stretch in three decades.
Sydney's maximums are forecast to remain below 30 through the remainder of this week, extending the run of sub-30C days to at least 327, the most since the record of 339 days from 1883.
A rare year without 'hot' weather
Considering Sydney's weather station averages 15.2 days above 30C each year, to record nearly an entire year without reaching 30C is exceptionally rare.
What makes this run even more irregular is in a global warming world the number of days where the temperature reaches 30C has been increasing during recent decades.
So far this century, the average has risen to 22 days per year and each year from 2017 to 2020 saw at least 30 days.
The last day above 30C was February 21, but Sydney did not record one day last year above the Bureau of Meteorology's threshold for a "hot" day, which for non-tropical coastal regions is 32C.
This means Sydney has not officially been "hot" in more than 12 months, as 2022 was the first year since records commenced in 1859 to stay below 32C.
Sydney only recorded seven days above 30C in 2022, well below the 30-plus days from 2017 to 2020
Where have the summer scorchers gone?
The mystery of Sydney's missing heat is a similar riddle to the record wet in 2022. The answer is blowing in the wind.
Averaged across an entire year, Sydney's most common wind is a westerly, however, in the past year the most common wind was an easterly.
During the warmer months, an easterly airstream is cooler than a westerly as the water temperature in the Tasman Sea, to our east, never climbs above about 23C.
That is well below the 45C air masses inland Australia is capable of producing during summer.
Even on days when a westerly, or a warm northerly, has blown across Sydney, either a sea breeze has developed by the afternoon or skies have been cloudy enough to keep the temperature below 30C.
When will Sydney finally reach 30C?
Through this week, winds will continue to blow from the east which should keep Sydney's maximums close to average.
The next chance of either a westerly or a northerly which could send Sydney to 30C is around the middle of next week, however, that is certainly not guaranteed and it will depend on the exact timing of afternoon sea breezes.
The all-time 1883 record of 339 days without reaching 30C is even under threat as the easterly wind deviation is forecast to continue into February.
