The Bureau of Meteorology's (BOM) climate models shows the pattern will remain positive in December and a high likelihood of persistence in January. Meantime, a negative Southern Annular Mode (SAM) will increase the risk of more westerly winds, the SAM pattern is expected to breakdown by late December.

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It is one of the strongest positive IOD events on record, BOM head of long-range forecasts Doctor Andrew Watkins said.

This means there is less rain-bearing weather systems and warmer than average temperatures for large parts of the country due to cooler than average water pooling off Indonesia, said Dr Watkins.

"We're also expecting a delayed onset for the northern monsoon, one of the key drivers for tropical rainfall during the summer months.

"We're expecting the onset of the northern monsoon by mid-summer, which should see the odds for closer to average rainfall increasing from January and into February."

Reports for spring show that NSW had one of the five driest springs on record. Overall, it was one of the ten warmest springs for the state with extreme heat in late November breaking spring temperature records in the southeast of the NSW. Most of the mainland topped 40 degrees at least once during November.

Low river flows were recorded at 89 per cent of locations in November, which means most mainland water storage are close to or below half full going into summer.

Dr Watkins urged people to stay alert to the potential severe weather risks over the coming months, including an increased risk of heatwaves and bushfires.

Learn more about predicting rain and managing climate risk:

For more information on the main drivers that influence climate in NSW visit Climatedogs: dpi.nsw.gov.au

Farmer and grazier Charlie Prell, Crookwell said water management is his biggest concern leading into summer.

The Prell property had around 450 millimetres of rainfall this year, much lower than the average of 780mm.

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"We had 5mm last week, and the last significant event was snowfall in early October, two months ago."

Mr Prell said the flow into spring-fed dams and rivers is falling. The Wollondilly River which runs through the Prell property has limited flow. This river leads into the Warragamba Dam that supplies more than 5 million people living in Sydney and the Blue Mountains.

"This is common in February and March, but not in November," Mr Prell said.

It slowed since the beginning of November.

"Spring-fed dams are running very slowly, but there is no certainty, we won't get through the summer without rain," Mr Prell said.

He is planning on further destocking of his mob of Corriedale sheep and 18-month old Angus cattle. Mr Prell will sell 150 ewes and around 400 lambs earlier than usual, as well as the cattle.

"We have rainfall records that go back to 1904 and the rainfall deficiency for this calendar year is as bad as it's been, including the Federation drought."

Mr Prell hasn't seen it this bad.

"It's been forecast for decades now that this is going to happen from the CSIRO, from the BOM and climate scientists.

"We need to start making plans to live in this new weather system."

For information on severe weather risks visit: bom.gov.au/knowyourweather

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