The first east coast low (ECL) of the year could be forming off New South Wales, with the potential to bring more than 100 millimetres of rain to parts of the state.
Forecast models first identified the low-pressure system would form in the Tasman Sea on Tuesday, but be far enough offshore not to meet ECL criteria.
However, the latest indicators are predicting it could pass just close enough to the NSW coast to impact communities, with heavy rain expected tomorrow and Wednesday.
ECLs are responsible for the majority of flood events along the state's coast and were behind several of the weather disasters which struck last year.
However, this week's system is considered marginal, and unlikely to bring widespread severe weather.
The peak of this event should occur late Tuesday and early Wednesday, with the most intense rain occurring south of the low's centre across the Mid North Coast, Hunter, and, possibly Sydney.
The coastal fringe could see more than 100mm of rain, possibly generating brief periods of flash flooding.
Winds will strengthen through Tuesday and may approach gale-force speeds in some areas.
Heavy rain fell over Sydney and the state's South Coast at the weekend — the Harbour City's official weather station at Observatory Hill collected 115mm in the 48 hours to 9am today.
That's just 12mm shy of the long-term April average.
Point Perpendicular, near Jervis Bay, has already received 142mm this month, which is more than the April mean.
The ECL will move away from the coast fairly quickly on Wednesday, keeping the worst impacts relatively short-lived and therefore preventing widespread flooding and wind damage.
The most notorious ECLs can linger near the coast for days and produce more than half a metre of rain, destructive winds, and severe coastal erosion.
What is an East Coast Low?
An ECL is a low-pressure system near the east coast of Australia.
One common list of criteria adopted to classify the more extreme events states an ECL is a low-pressure system which:
- Forms in an area between Queensland's Whitsunday Coast, and the Bass Strait
- Lingers within 200km of the coast for at least 12 hours
- Meets specific pressure gradient criteria (4hPA per 100km)
- Is associated with severe weather
ECLs are generally the most significant weather systems to impact the subtropical east coast of Australia, and, at peak intensity, have led to some of the costliest natural disasters in the nation's history.
There is around two severe events per year which generate daily rain totals in excess of 100mm.
