Sydneysiders should prepare for another day of heavy rain tomorrow, with warnings of more flash flooding.
The Bureau of Meteorology has issued a severe weather warning for coastal areas between the south coast and the mid north coast, with rain and thunderstorms hitting northern areas today before moving over Sydney tomorrow.
Sydney hit with flash flooding
It will be a grim week ahead for Sydneysiders as meteorologists warn the city is expected to reach the monthly rain fall levels within one week.
"Tomorrow is the biggest risk day for [flash flooding]," Bureau of Meteorology forecaster Deryn Griffiths said.
And it's set to be wet for most of the week in Sydney, Ms Griffiths said.
"For Wednesday our forecast is outright rain, possibly heavy at times.
"Then ... still quite a wet day on Thursday and then noticeably drier by Friday and the weekend."
The State Emergency Service urged people to stay away from flooded areas, creeks and stormwater drains.
Today 17mm fell in just 10 minutes in the city centre before 8am, Weatherzone head meteorologist Alex Zadnik said.
Mr Zadnik said that, outside tropical areas, flash flooding was generally expected if 15mm or more fell in one hour, so this morning's rainfall was particularly intense.
"We've already got some minor flooding of low lying roads and the like and it's likely to become worse through today and tomorrow," Mr Zadnik said.
The heavy rain caused traffic delays in some parts of the eastern suburbs as water flowed across the roads in peak hour.
A spokeswoman at the Transport Management Centre said there were some scattered delays on the train network this morning, but there were no major hold ups caused by the rain.
"The expectation is for the rain to become heavier through today, especially through the afternoon and night time," Mr Zadnik said.
"Heavier falls are likely to persist through Wednesday as well."
Sydney's average rainfall for April is 126mm, which is likely to be broken by falls this week.
"It's fairly likely that over the next three to four days we'll see that monthly average achieved," Mr Zadnik said.
"We should see over 100mm in the next three days, with the bulk of that falling today and tomorrow."
The wet weather was being caused by a deepening low pressure trough on the east coast, causing an increase in cloud and rainfall, he said.