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.