Such a set-up typically affects a wide region, so there would be well-above average maximum temperatures for many sites in NSW, he said.

The odds for record heat in any month - or day - have increased along with climate change. Australia has warmed about 1 degree over the past century.

Record run

Sydney had 13 days of at least 20 degrees last month, the most for any July, and one more than the previous record of 12 in 2013.

A seven-day run - broken narrowly by Monday's 19.9 degrees - was also the longest on record.

Most days in the coming week will be in the 21-23 degree range, or several degrees above the August average for Sydney of 17.9 degrees. There is almost no rain forecast.

According to the Bureau of Meteorology, most of NSW including Sydney has had its warmest temperatures on record for the first seven months of the year.

Other places posting record daytime temperatures include Brisbane and the Gold Coast, the ABC reported.

Sydney had just one day last month when the mercury failed to reach the long-run norm of 16.4 degrees.

Overnight temperatures were slightly above average - at 8.4 degrees - although many residents may feel it was particularly cold.

'Some reprieve'

A strong cold front is expected to sweep across NSW over the weekend, bringing "some reprieve" from the abnormal warm. The rest of August, though, looks like resuming the trend of above-average warmth, Mr Brittain said.

Rainfall may only be 1-5 millimetres for many locations in NSW but "any rain helps" given the worsening drought, he said.

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The relatively dry conditions also show little sign of letting up over the longer term, with the bureau forecasting the odds favour below-average rain for most of eastern Australia for August-October, especially this month.

Last month was the fifth-driest July on record for the state, and the fourth warmest, the bureau said.

Nationally, it was the driest July since 2002 with rainfall 49 per cent of the average.

El Nino looms

The bureau's latest El Nino report, released on Tuesday,  predicts thresholds used to declare an El Nino event will be reached by the spring, according to five of eight models they use. A sixth model places the timing at December.

During El Ninos, weakening easterly equatorial trade winds tend to result in less rainfall across eastern Australia.

Unfortunately for those farmers and fire authorities hoping for a rain break, Indian Ocean conditions are also favouring reduced convection off the WA coast, reducing the amount of moisture that is available to stream across the continent.

A so-called positive Indian Ocean Dipole "typically reduces winter-spring rainfall in central and southern Australia, and can exacerbate any El Nino-driven rainfall deficiencies", the bureau said.

Much of NSW has already had very much below rainfall for the first seven months of 2018.

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