Sydney's latest summer heatwave has peaked and temperatures are plummeting - but the relief won't last long as another hot spell will arrive within days.
Sydney Airport lost 10 degrees in a quarter of an hour, while the city dropped almost 8 degrees within 10 minutes of reaching its daily maximum of 39.4 degrees at 12.30 pm, the Bureau of Meteorology data showed.
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Tuesday marked the ninth day this summer of 35 degree-plus weather in the city, matching the previous record of the summer all the way back in 1895-96. A 10th such day is forecast for this Sunday.
A total fire ban is also in force for the greater Sydney and Hunter regions for Tuesday.
A slew of heat records are set to be rewritten for the month, with the city easily having its hottest January in terms of mean and minimum temperatures.Â
Tuesday's maximum will be enough for January's average maximum temperature to set a new high mark, exceeding the 29.5 degrees set in 1896, Rob Sharpe, a meteorologist with Weatherzone, said.
Richmond hit 43.2 degrees at its peak, making it a record seventh day above 40 degrees in January - backing up Monday's 43.8-degree scorcher. Many sites from Canterbury to Olympic Park also topped 40.
![An out of control bushfire on Tuesday afternoon near Neath in Hunter Valley.](/web/20170201184232im_/http://www.smh.com.au/content/dam/images/g/u/2/e/g/2/image.related.articleLeadwide.620x349.gu1ui4.png/1485841708479.jpg)
For western suburbs, it's likely to be only a "slow descent" compared with the eastern parts of the city as the cool change blow in, Mr Sharpe said.
"It's quite a shallow change," Mr Sharpe said, noting that the mountain ranges are likely to block much of it from reaching inland parts of the state that have had searing heat for days.
![Cooling off in Coogee before the heat arrived on Tuesday.](/web/20170201184232im_/http://www.smh.com.au/content/dam/images/g/u/1/w/2/6/image.related.articleLeadwide.620x349.gu1ui4.png/1485841708479.jpg)
Because the change is so weak, temperatures during the day and night are likely to remain well above average for another week.Â
The bureau is forecasting most of NSW will remain in at least a low-intensity heatwave for days to come, with severe conditions covering the eastern parts of the state for the three days from Friday:
![A cool change is expected to arrive by Tuesday afternoon - but the relief will be short-lived.](/web/20170201184232im_/http://www.smh.com.au/content/dam/images/g/u/1/v/u/y/image.related.articleLeadwide.620x349.gu1ui4.png/1485841708479.jpg)
![](http://web.archive.org./web/20170201184232im_/http://www.smh.com.au/content/dam/images/g/u/1/u/j/l/image.imgtype.articleLeadwide.620x0.png)
On current forecasts, the city will have a relatively mild couple of days with tops of 27-29 from Wednesday to Friday, before another string of days in the 30s. Nights should remain above 22 degrees for another week.
For places such as Richmond, another three days of 40 degrees or warmer are tipped from Saturday.Â
There is little rainfall expected over the coming week after another relatively dry month. In January, the city collected 48 mm of rain, slightly less than half the average for the month.
Other coastal areas were relatively dry, increasing the risks of a busy late-season fire period. (See bureau chart of rain in NSW below.)
![](http://web.archive.org./web/20170201184232im_/http://www.smh.com.au/content/dam/images/g/u/2/e/c/l/image.imgtype.articleLeadwide.620x0.png)
Fire crews were attending a series of fires near Neath and Aberdare in the Hunter region around Cessnock.
That area has had a string of exceptionally warm days, and on current bureau forecasts will cop four days of 40 degrees or more from Saturday.
Record heat
​2016 was Sydney's hottest year on record. With last month the city's second-hottest December and now January going one better, this summer is well on course to be Sydney's warmest.
The extended heat is having various impacts, including lifting Sydney's water usage to levels not seen since the drought of the early 2000s.
The city consumed 2.182 billion litres of water on Monday, the most since January 29, 2003, Sydney Water said.
"To illustrate the intense summer conditions this year, the average water demand for January so far is 1.762 billion litres per day, which is 19 per cent higher than the 10-year historical average demand" for the month, Peter Hadfield, Sydney Water spokesman, said.
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