As at 8am Friday, the most rain in the state has fallen in Byron Bay, with 281 millimetres of rain recorded since 9am on Thursday.
The coastal trough, which at about 6am was near the northern NSW coast, is expected to deepen and gradually shift southwards, increasing rainfall along the central and southern parts of the coast and adjacent ranges during Friday and over the weekend.
“It seems likely the rain in Sydney will remain steady throughout today, increasing throughout the afternoon and into the night, which will bring windier conditions overnight and tomorrow morning,” bureau forecaster Gabrielle Woodhouse said on Friday morning.
The bureau has issued a severe weather warning for damaging winds and heavy rainfall for the Northern Rivers, Mid North Coast, Metropolitan and parts of the Hunter, Illawarra, Central Tablelands and Northern Tablelands forecast districts.
For some areas, intense rainfall and gusty winds of up to 90km/h are possible with thunderstorm activity, or with the formation of smaller lows embedded within the coastal trough, the bureau said.
“Heavy rainfall, which may lead to flash flooding and riverine flooding, is possible for parts of the Northern Rivers, Mid North Coast, eastern parts of the Northern Tablelands and parts of the Hunter today,” the bureau said early on Friday morning.
“From later Friday afternoon or evening, the focus shifts further south to include the Sydney Metropolitan, Illawarra and eastern parts of the Central Tablelands (including the Blue Mountains) forecast districts.”
A flood watch and flood warning has also been issued. Locations which may be affected include Lismore, Grafton, Coffs Harbour, Port Macquarie, Taree, Newcastle, Gosford, Sydney and Wollongong.
The road to the Jenolan Caves, southwest of Katoomba, has been closed due to fears the heavy rain could cause landslides.
“There are also a significant number of loose rock fragments which have an increased likelihood of rolling down the slope and on to the road,” a Transport for NSW spokesman said.
“Given current weather forecasts are predicting heavy and prolonged rainfall in the area over the coming days – the first in the area since the bushfires – it is essential for safety reasons that the road is closed until it can be assessed safe for traffic.”
NSW Maritime executive director Mark Hutchings says conditions are also dangerous out at sea.
“Skippers and owners of small boats should be on high alert and check the conditions before considering crossing a coastal bar or heading offshore,” he said in a statement.
The wet conditions have resulted in the number of active fires decrease by nearly a third since Wednesday, in one of the biggest single-day drops since the fire season began.
At the end of Wednesday, there were 62 active fires around NSW and the ACT – as of 7pm Thursday, there are 42.
The roughly 1200 firefighters across the state “achieved a lot of progress” on Thursday, whether that’s been slowing the spread of fires, or containing fire fronts.
Currently, no fires are above advice level, and just two of the 21 total fire areas have a rating above “low-moderate” for Friday.
Mary Ward is Deputy Lifestyle Editor of The Sydney Morning Herald and The Age.