Sydney has one more "danger period" of heavy rains and winds to endure before the city finally gets a break in its wettest two-day soaking in 18 years.

In its latest severe weather warning for the Metropolitan and Illawarra regions, the Bureau of Meteorology said the most severe conditions have peaked but brief periods of damaging winds with gusts of 100 km/h are possible along the coastal fringe. The warning for the Hunter region has been cancelled.

"Heavy rain and thunderstorms, which may lead to flash flooding are forecast for parts of the Metropolitan and Illawarra forecast districts although conditions will gradually improve into this afternoon," the bureau said.

The damaging east coast low that lashed Sydney with its strongest sustained winds this century and dumped about 230mm of rain since 9am on Monday has now split into two centres as its strength weakens, Brett Dutschke, senior meteorologist at Weatherzone, said.

Still, another belt of storms will dump a further 15-50mm of rain over the city on Wednesday, with the heaviest falls likely to be in the eastern suburbs.

Although wind speeds will be lower than overnight, the continued rain and gusts will most likely bring down more trees, adding to the clean-up needs once the tempest has passed.

"These next few hours between now and about lunch time for the city and the east, through to about 4pm for the west, are the danger period," Mr Dutschke said.

"There's certainly enough rain to soften trees more and winds are still going to be strong enough to take advantage of those that have almost come down," Mr Dutschke said.

The main core of the low is located about 100 kilometres off the Central Coast and will be largely stationary on Wednesday as it weakens, he said.

As is typical with east coast lows, another smaller low has developed east of Batemans Bay to Sydney's south, and will bring strong winds and heavy rain to the Illawarra and the South Coast later on Wednesday morning and afternoon, Mr Dutschke said.

The bureau also recently updated its flood warning for the Hawkesbury River, predicting minor flooding at Menangle Bridge, while minor flooding at the Colo River at Putty Road and along the Hawkesbury at North Richmond is already under way.

The good news is that breaks in the rain will increase, and temperatures will warm.

Wednesday's forecast high of 20 degrees will be followed by 23 on Thursday and 25 on Friday, according to the bureau's forecasts.

Weatherzone is owned by Fairfax Media, publisher of this website.