Sydney could almost double its rain so far this year in just a week, with wet conditions not unlike an east coast low developing along the NSW in coming days, meteorologists say.
The "main bulk of the rainfall" will be falling over the weekend, Jordan Notara, a duty forecaster for the Bureau of Meteorology, said. "We are expecting a low to form off the coast on Friday."
While it's more likely to be a "Tasman low" than the more damaging and drenching east coast low variety, coastal regions near the system will likely see steady rain with the potential for flooding, Mr Notara said.
"We have a perfect recipe for persistent rainfall along the eastern seaboard regardless of an east coast low occurrence," Jacob Cronje, a senior Weatherzone meteorologist, said. "It almost looks monsoonal."
The bullseye for rainfall is now forecast to centre around the Sydney region, but that could shift in coming days as models get a better fix on unfolding conditions.
Any low that develops within the deepening trough that is now sitting off the east coast will draw moisture from the unusually warm coastal waters that have been a feature for months.
An east coast low also remains a chance, and should one form, the rain should last longer and be heavier - along with stronger winds - than is currently expected, Mr Cronje said.
"Sunday could be quite as wet as Saturday," he said, adding "Mardi Gras is going to be wet" for the Saturday march through Sydney.
On current forecasts for the coming eight days, Sydney's rainfall could exceed 200 millimetres for the period, compared with 202.6 mm for February and a relatively dry 48.4 mm in January.
(See bureau chart below for eight-day rainfall totals for Australia.)
On current forecasts, Sydney can expect 8-15 mm on Tuesday, 10-25 mm on Wednesday and 5-10 mm on both Thursday and Friday, the bureau says.
At this point, Saturday is looking at 8-25 and Sunday 5-15 mm, with conditions similar early next week.
Temperatures are likely to remain fairly range-bound through the week, with overnight minimums around 20-21 degrees and tops of 26-27 degrees each day.
Despite the wet spell being "a vast difference" from what Sydney has seen in recent months, the longer term outlook for autumn is likely to see a reversion to the warmer and drier than average conditions of recent months, Mr Notara said.
