Flash flooding, heavy rain expected across NSW

The BoM has issued a flood watch, with a low-pressure system likely to dump heavy rain on coastal areas from Wednesday.

Dangerous driving conditions expected - be careful.

Sydneysiders are being warned to brace themselves for wild weather with heavy rainfall expected to cause flash flooding in the city and elsewhere across New South Wales.

The Bureau of Meteorology on Monday issued a flood watch and severe weather warning with a low-pressure system likely to dump heavy rain on coastal areas from Wednesday morning.

Take care on the roads. Picture: istock.

Flash flooding, damaging winds and hazardous surf conditions are anticipated. Bureau forecaster Anita Pyne says the heaviest falls will likely be over the Sydney and Illawarra districts but the northern part of the South Coast, Central Coast and Blue Mountains could also be hard hit.

The majority of the storm will be over in a six to 12-hour period from Wednesday morning.

Sydney and the Illawarra are predicted to receive up to 100 millimetres of rain with localised totals that could exceed 200mm, Ms Pyne said in a statement.

The NSW SES warns the Upper and Lower Nepean rivers, the Hawkesbury River, the Colo River and Georges and Woronora rivers could experience minor to moderate flooding.

Rivers likely to swell. Picture: istock.

The Central Coast, northern Sydney and southern Sydney can expect localised flooding as will the Upper Coxs River, Macdonald River, Parramatta River and the Illawarra Coast which are also predicted to experience riverine flooding.

The SES issued a warning to those who live in potentially affected low-lying areas to prepare for flooding by sandbagging doorways, ensuring gutters and drains are clear of debris and preparing for possible evacuation.