Sydney broke a century-old temperature record this week with little fanfare, and almost completely without weather-watchers noticing.
From 18 October until 19 April, temperature readings at Sydney’s Observatory Hill reached or exceeded 20C. That 184-day run was snapped by Thursday’s meagre 19.8C reading, according to the Bureau of Meteorology.
The previous record was a 180-day sequence of 20C or warmer days that ran from 6 November 1913 to 4 May 1914.
Ben Domensino, a senior meteorologist with Weatherzone, said the long run without a notable cold spell was “amazing” given it began during the tail end of a La Niña event that delivered record rainfall in Sydney, including the wettest October, according to bureau data going back to 1859.
Domensino said such records might seem harder to break during wet spells because clouds and rain tended to keep a lid on daytime temperatures. “We haven’t had a shortage of those.”
Miriam Bradbury, a senior bureau meteorologist, said the La Niña event meant there was often less temperature variation between days and nights.
A positive phase of the southern annular mode, another of Australia’s key climate drivers, also meant moist onshore winds were dominant in the Sydney region during the October-December months, in particular, Bradbury said.
“Throughout that period, we had warmer-than-average sea-surface temperature [in the Tasman],” she said. “That really helped maintain warmer-than-average conditions.”
Climate change increases the odds that warm records will be broken – with fewer cold ones being exceeded. According to the bureau, Australia’s temperatures have risen on average 1.47C over the period since 1910.
For Sydney, average maximum temperatures have been edging higher across the year, particularly during the cooler months.
Sydney's mean maximum temperatures have been trending higher across the year, particularly in the cooler months. (Source: @BOM_au ) pic.twitter.com/o5mk7w8Ci0
— @phannam@mastodon.green (@p_hannam) April 21, 2023
Domensino said the most unusual part about Sydney’s stretch of warmth was the absence of days of less than 20C in the second half of October and during most of April.
“These cooler months on either side of summer would typically produce more sub-20C days,” he said, noting October was particularly wet. Sydney collected 295mm of rain for the month, about roughly four times the typical 76.7mm rainfall.
“Sydney’s hottest March on record also helped produce this long spell of days equal to or warmer than 20C,” Domensino said.
Bradbury said a series of inland troughs over Queensland and New South Wales had helped keep out cold fronts from the south.
The near-miss on Thursday prevented the record run extending at least another week. The mercury cleared 21C in the city on Friday and was forecast to reach 22 to 24C over the coming days until at least next Thursday, the bureau said.
“Basically we’re seeing a really big high-pressure system over Victoria,” Bradbury said, adding the next chance for a cold front to move through was towards the end of next week.
