Just 14 days into the month, Sydney has recorded its wettest July on record. 

The Bureau of Meteorology (BOM) has reported 342.2 millimetres of rainfall at Sydney's Observatory Hill, smashing the previous monthly record already. 

"The previous record for July was 336.1 millimetres from 1950, but that rain fell over a whole month," Weatherzone meteorologist Ben Domensino said. 

"So, to see more than that just in one half of the month is nothing short of extraordinary," he added. 

This month's east coast low dumped heavy rainfall across much of the greater Sydney basin, marking 2022 as the city's wettest year on record to date. 

As of July 14, Sydney's running annual rainfall total sat at 1,889.6mm, according to Weatherzone data. 

That is more than 300mm more than the previous record of 1,581.1mm taken on the same date in 1891.

"That's very significant because Sydney, the rainfall observations at Sydney's Observatory Hill, go all the way back to 1858," Mr Domensino said. 

"So, we're talking about more than 160 years of records here — and not only did we beat that up to this point in the year, but we've beaten it by more than 300 millimetres." 

Mr Domensino said several factors were behind the record falls, including La Niña and a positive Southern Annular Mode, a climate driver that has increased the chance of winter rain in eastern Australia. 

While Sydney has not yet broken the annual record rainfall of 2,194mm, set in 1950, the harbour city is not far off — and experts say it is a record we are likely to break. 

"We only need another… about 200 to 300 millimetres to get to that annual record — and we've still got a few months to go," Mr Domensino said. 

"So, I think at this stage, there is a good chance we'll see this being the wettest year on record before we get to the end of December." 

Agus Santoso from the UNSW Climate Change Research Centre said the state could be hit with yet another La Niña weather event at the end of this year.

"The models that we look at point to a 58 per cent chance of having another one," he said.

NSW has faced two La Niña weather patterns in two years, with the latest ending in June.

If it were to return, Dr Santoso said it would become a "triple La Niña".

"A triple La Niña ... means three La Niña's, three years in a row... [it] is actually quite rare," he said.

"Since 1950, we've had just two triple La Niña's."

For a state still recovering from widespread flooding, he acknowledged further rain was largely unwanted.

"The catchments are already full. The dams are already full. The prospect of another wet condition, that is not very good news," he said.