Victorians mopping up after recent heavy rain could be forgiven if they were too busy to reflect for long on the remarkable heat that precede the downpours.
The Bureau of Meteorology, though, has tallied the many records for Victoria and Tasmania during the blistering end to spring in a special report it released on Monday.
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| St Kilda beach during one of record-breaking stint of warm evenings in Melbourne last month. Photo: Joe Armao |
In Melbourne, the 12 November days with temperatures topping 30 degrees eclipsed the previous record of 10, set in 2009.
Overnight temperatures were consistently mild, with Melbourne clocking up 14 consecutive nights above 15 degrees – easily beating the previous record stretch of nine nights in a row, also set in 2009.
The city had previously not recorded such a warm spell before January.
The source of the remarkable warmth was a high-pressure system over the southern Tasman Sea that barely budged for a fortnight, drawing a steady stream of warm inland air over the country's south-east.
"Such an extended, uninterrupted period of warm weather is unusual in spring, when weather systems are normally more mobile than they are in late summer and autumn," the bureau said in its report.
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| Enjoying the warmth while it lasted, on South Melbourne beach at the end of November. Photo: Justin McManus |
The final 12 days of the month averaged above 20 degrees, eclipsing 10-day runs in 1959 and 2009.
Similarly, the state's 21 days in a row of minimums above 10 degrees easily beat the previous 16-day stretches in 2000 and 2009.
The state's average mean temperature was more than 3 degrees above the 1961-90 average. It was only the sixth time Victoria has notched up so large an anomaly for any month, the bureau said.
Off the charts
In Tasmania – which has seen snow overnight – the November records were even more off the charts.
Average maximum temperatures for the state came in 3.79 degrees above the long-run norm.
That beat the previous record anomaly of 2.09 degrees set in 1914 by a whopping 1.7 degrees, and was the largest departure from the average maximum for any month.
Hobart's six consecutive days of 25 degrees or warmer weather equalled the record for any time of the year. Previous such stints had all occurred between January and March.
"In some cases, particularly in southern and western Tasmania, the length of the warm spell was unprecedented for any time of year," the bureau said. "Many records were set for consecutive days with maximum or minimum temperatures above thresholds."
One gauge of the influence of the high pressure over the region was Hobart setting a mean sea level pressure record for November of 1019.6 hectopascals, edging the previous high for the month set in 2007 of 1018.8 hPa.
Warm waters
The waters around both Victoria and Tasmania were also unusually warm, especially around the south west of the Apple Isle. (See bureau chart below for the week of November 20-26.)
"By the end of the month, all of the waters surrounding Tasmania were 3 degrees above [the 1971-2000 average] and ranked as some of the highest values on record," the bureau said.
"These high temperatures existed in the top layer of the ocean only and were caused by low cloud coverage and light winds," the bureau noted.
This placed the event in contrast to a marine heatwave at the end of 2015 driven by an eddy that had spun off from the East Australian Current.
As reported by Fairfax Media last month, waters off south-eastern Australia have recently been one of a handful of global hot spots, relative to the average for this time of year.
Sea-surface data from Australia's Integrated Marine Observing System also demonstrate how unusually warm this patch of water is compared with the rest of the region. (See chart below for November 30.)
The bureau's report noted how the blocking high pressure also contributed to milder conditions further up the east coast of Australia.
Sydney, for instance, barely notched an above-average month for maximum temperatures. Virtually all of the coast further north to Cape York in Queensland had a below-average November for daytime temperatures.
Those warm waters are currently contributing to a deep low-pressure trough off the south coast of NSW, that is likely to bring heavy rain to the region on Monday.
"When sea-surface waters are warmer there is more evaporation and a better moisture source," Jiwon Park, a bureau forecaster, said. The contrast with land, which typically cools off at night, was creating in effect a "stationary front" offshore.
The bureau has issued a warning for falls of more than 100 millimetres over a 24-hour period from Monday afternoon for an area stretching from the Illawarra south almost to the Victorian border.
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A flood watch is in place for six river catchments in the region.
Warm spring
For Australia as a whole, temperatures last month were above average for minimum, mean and maximums, but less unusually so than the previous two months.
For spring as a whole, all but South Australia and the Northern Territory recorded a spring in the top 10 warmest, in national data going back to 1910, the bureau said in a separate report.
For Victoria, spring was the fourth-warmest for minimum and mean temperatures, and the sixth warmest for maximums.
Tasmania was again the standout, posting its warmest spring on record for mean temperatures – edging out 2005.
It was also the second warmest spring for the state, trailing only 1914, the bureau said.
Warm spring
For Australia as a whole, temperatures last month were above average for minimum, mean and maximums, but less unusually so than the previous two months.
For spring as a whole, all but South Australia and the Northern Territory recorded a spring in the top 10 warmest, in national data going back to 1910, the bureau said in a separate report.
For Victoria, spring was the fourth-warmest for minimum and mean temperatures, and the sixth warmest for maximums.
Tasmania was again the standout, posting its warmest spring on record for mean temperatures – edging out 2005.
It was also the second warmest spring for the state, trailing only 1914, the bureau said.
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