Sydney weather LIVE: Rain and wind to lash state with worst yet to come

The branch which fell on the track near Artarmon station has been removed, but commuters are still advised to expect delays if travelling on the T1 North Shore Line this morning. 

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 told AAP.

"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."

Buses are replacing ferries between Parramatta and Rydalmere after the Parramatta Weir overflowed this morning. Up to 30 millimetres of rain fell in the region overnight. Commuters are advised to allow extra time.

At Engadine, there is flooding in the southbound lanes of the Princes Highway approaching Anzac Avenue. 

The NSW State Emergency Service are reminding motorists to take extra care this morning and not drive through floodwater. 

There are delays on the T1 North Shore line after a tree branch fell onto the track at Artarmon earlier this morning.

Some services are being delayed by 10 minutes and stopping patterns may change at short notice, Sydney Trains advises.

Meanwhile, flooding has been reported at Northbridge and Roseville.

There is flooding in both directions of Strathallen Avenue near Cliff Avenue at Northbridge. There has also been flooding reported in the northbound lanes of Boundary Street near Babbage Road at Roseville.

Motorists are advised to take care and not attempt to drive through floodwater.

Oxford Falls Road is also closed between the Wakehurst Parkway and Aroona Road, due to flooding. Motorists are being advised to avoid the area.

The Rural Fire Service have said they were "over the moon" with the rainfall on Thursday evening, as rain arrived across many parts of the state, including the north coast.

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.

Good morning and welcome to what is expected to be a very wet morning to start a predicted week of rain for Sydney and the NSW northern coast.

Up to 130 millimetres of rain could fall in Sydney on Friday alone, with the worst of the weather set to hit the city by Friday afternoon and evening, when flash flooding could occur. Up to 90 millimetres of rain could fall again on Saturday, and 80 millimetres on Sunday.

Over 40 millimetres of rain was recorded at Sydney's Observatory Hill before 6am.

A severe weather warning has been issued for Sydney, the Illawarra and Mid North Coast, as well as parts of the Northern Rivers, Hunter, Central Tablelands and Northern Tablelands.

We will be bringing you updates throughout the morning. Don't forget to pack a brolly!