The weather station on Observatory Hill in the CBD has recorded 822mm of rain so far this year.
That's about 70 percent of the amount that would normally fall in a year, or what would have accumulated by August.
The wet start has broken the previous record of 783mm up to 8 March, which was set in 1956.
The third wettest start to the year was recorded in 1990, when 754mm of rain fell.
Reprieve from the weather is forecast for Thursday as the east coast low moves offshore.
But until then the Bureau of Meteorology (BOM) warns more rainfall in already soaked catchments is likely - and dangerous.
"Even though the sun does come out, we are likely to see many of these rivers continuing to experience major flooding," BOM meteorologist Dean Narramore said.
"And for some, the flood peak won't occur until Wednesday or Thursday."
Of particular concern are the Hawkesbury and the Nepean Rivers which Narramore said were in danger of experiencing flooding levels "equal to or greater than what we saw in March of 2021."
Both rivers were under flood warnings late last night and were being "monitored upstream" with surrounding areas still subject to evacuation orders.
Premier Dominic Perrottet also acknowledged there was "loading similar" to last year's floods, as he urged residents to follow the State Emergency Service's (SES) advice during this "difficult time".
It comes as a mother and son became the first victims of Sydney's flood emergency.
Hermalathasolhyr Satchithanantham and Bramooth's bodies were found in a swollen creek in Western Sydney about 1.5 kilometres from where their car crashed into a stormwater canal.
A member of the public first spotted the 67-year-old woman's body, soon after her 34-year-old son was found about 400 metres upstream.
Sydney's weather event could be further complicated today with strong winds that developed overnight.
SES spokesperson Andrea Cantle fears trees may fall due to overly saturated soil and has urged the community to be "as careful as possible".
"We're asking people to avoid the road," Cantle said.
"With properties, put away any loose items, bring your pets indoors because it's going to get quite windy, the rain may die down and the wind will pick up."
Overnight there were 65 evacuation orders across the state, impacting more than 60,000 people.
Cantle said they were mostly in the Hawkesbury and Nepean River area, Campsie, Singleton in the Hunter and Sussex Inlet on the South Coast.
"We're asking if you're affected by an order to memorise that evacuation route and acknowledge that the road access could be cut, as well as power, phone and internet," she said.
Among the suburbs affected were McGraths Hill and Mulgrave in Sydney's north west where residents were given until 8.30pm to leave via Windsor Road to Rouse Hill.
While residents around Narrabeen on Sydney's northern beaches were given the all clear to return home overnight after flash flooding yesterday, some locals in the Hunter and the Hawkesbury regions were forced to evacuate last night.
Residents in low lying areas of Scone in the Hunter were given 90 minutes notice and told to be out by 3am because of rapidly rising floodwaters.
Those opting to stay were warned by the SES they may not be rescued because it could be "too dangerous".
In the northern beaches, Mona Vale recorded 102mm of rain in just three hours yesterday as residents in parts of Narrabeen were given until 7pm to evacuate via Pittwater Road.
Those in properties around the lagoon were also told by the SES staying meant risking being "trapped without power, water or other essential services".
By midnight residents were issued with a Return with Caution notice after flood levels dropped.
Earlier, initial readings of water levels at Manly Dam also prompted a red level evacuation alert for 800 homes in the low-lying areas below.
The warning at the 1892 built facility was later downgraded to amber with nearby residents told to be ready to evacuate.
"The rain and thunderstorms have not finished yet," SES Commissioner Carlene York said.
"There is a chance that [the dam] may go over that area and we may go back up into that evacuation order."
A Manly local helping move people to higher ground told the ABC the rainfall had caught him off-guard.
"I don't think we have seen rain like this. I was getting updates. My feet were [under], ankles and then, 'Oh, that's my car floating down the street'," he said.
Photo: AFP Caption: A container floats in floodwaters in a commercial area of the Sydney suburb of Camden, 8 March.