July is traditionally Cessnock's driest month with an average total of 28.8mm, according to the Cessnock Airport weather station records dating back to 1968.

By 9am Tuesday, 137.2mm had fallen at the airport this month, eclipsing the previous record of 124.8mm, set in 1999.

A new daily record for July - 80.6mm - was set in the 24 hours up to 9am Monday (the previous record was 55.2mm, set on July 27, 2020).

With 73mm falling in the 12 hours up to 9pm Tuesday, and the rain set to continue overnight, the daily total could be broken again come Wednesday morning.

AS IT HAPPENED: Evacuation order for Wollombi, Testers Hollow closes as natural disaster declared in Cessnock

The Bureau of Meteorology says this week's heavy rainfall along the eastern New South Wales coast can be linked to changes to several climate drivers.

"While the Bureau's latest climate driver update confirms the 2021-22 La Nina has ended, there are several other climate influences associated with above-average rainfall in eastern Australia," a bureau spokesperson said on Tuesday.

"The Bureau's 2022 winter outlook showed above average rainfall over the coming months, particularly for most of eastern and northern Australia, due to warmer than usual waters around the continent and more moisture-filled air being directed into eastern Australia.

"The July rainfall event was influenced by the Indian Ocean Dipole, likely to become negative in the coming months, and the positive Southern Annular Mode (SAM).

"The Indian Ocean Dipole (IOD) refers to the difference in sea surface temperatures between the western and eastern Indian Ocean. In the negative phase, warmer waters concentrate near Australia, leading to above average winter-spring rainfall as more moisture is available to weather systems crossing the continent.

"The SAM refers to the non-seasonal, north-south movement of the strong westerly winds that blow almost continuously in the mid- to high-latitudes of the southern hemisphere. In the positive phase, the SAM directs more moisture-filled air than usual into eastern Australia, driving above average rainfall and more east coast lows in winter.

"During this recent rainfall event, very warm waters off the Australian coast (21-23°C) provided extra energy and moisture contributing to the deep trough and east coast low, leading to the relative concentration of the heavy rainfall to one 24-hour period."

A natural disaster area has been declared in the Cessnock local government area for the second time this year, following the floods in March.

Assistance is being provided through the jointly-funded Commonwealth-State Disaster Recovery Funding Arrangements, and may include:

The Wollombi Valley, which copped the brunt of the March flood, was also badly impacted by this week's severe weather, with an evacuation order issued on Tuesday evening.

The Wollombi Tavern was inundated with floodwater around lunchtime, and the major flood level of 12.2m was broken and the Bureau of Meteorology was predicting it to reach 13.5m - about 200mm higher than the flood during the 2007 Pasha Bulker storm - later on Tuesday.

As night fell on Tuesday the waters were rising around Swamp Creek in Abermain and Weston, where residents were bracing themselves for a repeat of the 2007 and 2015 floods.

Meanwhile at Testers Hollow - where work is under way to construct a flood-proof road - was cut off for the sixth time in 15 years.

The road was closed around 7.30am Tuesday, and by nightfall the floodwater had reached the height of the new road, which is due to be opened in 2023.

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