Flooding in NSW, longest wet spell in Sydney possible with rain forecast to continue into this weekend

More wet weather is expected for New South Wales this week, with rain tipped to intensify this weekend. (Supplied: Peter Beard)

Rain will continue to drench eastern NSW for another six days, including another round of heavy falls this weekend, which have the potential to bring flooding to the southern half of the coast.

The prolonged wet spell, now up to day 9, is due to a complete breakdown of the standard eastward movement of weather systems around Australia.

It has allowed a region of high pressure to remain near stationary west of Tasmania since last Tuesday.

For NSW, the high’s position is leading to a continuous flow of moist south-easterly winds and showers on the coast, but what’s unusual about this event compared to a typical blocking high is its longevity — a feature which will ensure this May finishes as one of the wettest on record for NSW.

The unusually monotonous pattern, now well into its second week, could even produce Sydney’s longest wet spell on record.

Widespread rain to return — flooding likely this weekend for NSW coast

Showers of fluctuating intensity and frequency will continue across eastern NSW during the coming days with an average fall of around 5 to 10mm every 24 hours.

In the meantime, another band of rain will rapidly form across the nation’s interior as tropical moisture moves south and runs into a wave of cold air aloft.

The pattern is remarkably similar to last week’s rainband, however on this occasion, rain will be slightly more widespread.

It will extend from about Mount Isa to Broken Hill on Thursday, before spreading south-east on Friday to northern Victoria and the NSW western plains.

The band will then shift to the NSW coast and ranges through the weekend, again replicating last week’s system.

The greater risk of heavy falls this weekend is thanks to a deeper trough forming along the coast, a region where moist air converges at the surface and rises into thick rain producing cloud.

Between Friday and Monday around 100 to 200mm could fall on the southern half of the coast, enough to trigger flooding according to the Bureau of Meteorology (BOM).

“The flood risk for New South Wales over the coming days remains elevated, particularly from the Hunter through the south coast of the state, where soils are already saturated,” a BOM press release stated.

Pockets of heavy rain in excess of 50mm and minor flooding could also impact the state’s north coast and west.

Heavy rain is then likely to ease along the coast early next week as the trough moves offshore, while simultaneously the stubborn high-pressure systems finally drifts east towards New Zealand – thus ending the blocking pattern that has dominated the nations weather for two weeks.

Wet spell brings wettest May in decades

Even before heavy rain arrives later this week, the blocking pattern has delivered the heaviest May rain in more than a decade to parts of the Central Coast, including 252mm at Swansea, already the highest total since 2001.

Totals this month have exceeded 100mm from about Forster to Ulladulla, increasing to more than 200mm between Newcastle and Sydney and around Jervis Bay.

By 9am Tuesday a handful of the wettest locations so far this month include:

• Hamlyn Terrace 319mm
• Swansea 252mm
• Point Perpendicular 225mm
• Gosford 221mm
• Jervis Bay 214mm

Sydney’s wettest suburb has been Cronulla with 190mm to 9am Tuesday, while the city has collected 127mm, already exceeding the May average of 117mm.

Rain was also widespread last week across the state’s west, and totals in many towns from the northern Riverina to the upper west have also exceeded their monthly average, including Hillston where 66mm fell in the 24 hours to 9am Saturday, the town’s wettest May day on record.

All-time record long run of rainy days possible for Sydney

The run of rainy days (at least 1mm) for Sydney has now reached eight, and with wet days nearly guaranteed until at least Monday, that figure is almost certain to reach 13, just short of the all-time record of 16 days from 2022 and 1943.

Considering some modelling indicates a few showers could continue through to the middle of next week, there’s the slight possibility the record could be threatened.

The record number of days with at least 0.2mm, the smallest amount observed, is 29 from 1893.