Parts of the Sydney Basin are likely to get their longest spell of early-season heat on record, giving residents and visitors yet more reason to hit the beaches.
Penrith, Bankstown and Richmond could all bask in four consecutive days above 33 degrees in a heatwave that began on Saturday, James Casey, a meteorologist with Weatherzone, said.
Penrith is forecast to reach 37 degrees on both Monday and Tuesday, with Richmond likely to peak at just a degree or so cooler.  
Sydney's Observatory Hill won't be quite that hot but a trio of days 33 degrees or warmer from Sunday to Tuesday, if reached, would be the city's warmest   October run since 2004, Mr Casey said.
So far on Monday, the city's mercury has nudged 34.6 degrees, compared with the long-run average for   October of 22 degrees. Olympic Park has reached 35 degrees.
North-westerly winds are streaming in from the hot, dry inland regions of the country. These pushed humidity levels to just 15 per cent on Sunday, down from 50-60 per cent a day earlier, he said.
Climatologists are gathering the numbers on the burst of heat, with places such as Mildura in north-western Victoria setting a 37.5 degree early-season record on Sunday.
That record may last all of one day with another scorcher of 39 degrees forecast for the town on Monday.
Melbourne's AFL grand final was played in record heat of 31.3 degrees - a high point for that date, not just because the season's decider was played about a week later than usual.
The NRL thriller in Sydney on Sunday night fell just 0.2 degrees shy of the record warmth for the final, a mark set just a year ago, Mr Casey said.
Nobbys Head, near Newcastle, may be another site recording exceptional heat, with its longest spell of 30-degree days in   October likely to be set at four after Tuesday, he said.
Dry times
The abnormal warmth is coming as inland regions rapidly dry out.
The combination of the strengthening El Nino in the Pacific and unfavourable conditions for rainfall generation from the Indian Ocean off north-west Western Australia are creating unusually dry conditions almost nationwide.
The Bureau of Meteorology, for instance, recorded almost no rainfall for Australia in the 24 hours to 9am on Sunday, with a similar forecast for Monday.
The day was so dry that the falls averaged just 0.02 millimetres across the country, a reading noted on only a couple of dozen days of bureau records, according to the bureau.
Last month was also Australia's third-driest   September since records began in 1910, the bureau said last week. 
Nationally averaged rainfall was just a third of average levels, with NSW coming 55 per cent below and Victoria collecting about half as much as typical for   September.
Outlook mixed 
A southerly change on Wednesday morning will bring a sharp retreat in temperatures for Sydney, with a top of 23 degrees forecast. That compares with Monday's expected top of 33 degrees and 29 degrees tipped for Tuesday.
The change, though, is unlikely to bring more than the odd shower for the city on Thursday through to Sunday.
"It doesn't look like there's a lot of moisture in it," Mr Casey said.
Gusty winds may make conditions tricky for firefighters if any blazes are under way, but they don't look like being particularly strong at this point, he said.
The entire NSW coast has a "very high" fire danger rating on Monday.
Temperatures for Sydney are likely to start to climb again from Sunday, and the longer-term forecasts point to more heat building from the west from the middle of the month, Mr Casey said.
While Adelaide may get days in the mid-30s, Sydney and Melbourne may miss out on the worst of the heat if a weak change keeps the warmth further north and west of the cities, he said, noting forecasts that far out can be subject to significant change. 
Canada's meteorological service offers some support to that outlook, though, indicating that south-eastern Australia will be among much of the planet likely to experience above-average temperatures in the week from   October 12, as seen in the map below.
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