A low pressure system is deepening off the NSW coast and will bring further heavy falls to the Illawarra, mainly south of Wollongong, as well as the South Coast.

The system is generating vigorous onshore winds along the South Coast, and bringing periods of heavy rainfall to the region. 

The low is expected to reach peak intensity this afternoon and evening, before moving slowly northeast away from the coast later on Tuesday night and gradually weakening during Wednesday.

Periods of heavy rain, which may lead to flash flooding are forecast for the Illawarra and northern parts of the South Coast. Locations which may be affected include Wollongong, Kiama, Nowra, Jervis Bay and Ulladulla.

Any flooding will initially affect low-lying areas and flood-prone local roads.

The NSW SES advises that people in the Illawarra and South Coast areas should watch the weather and look out for flood waters near their properties.

Farmers located on the floodplain should be ready to move pumps, other equipment and livestock if floodwaters rise.

People should avoid walking or driving through floodwaters, which could be deeper or faster-flowing than they look. Children, in particular, should be kept away from streams and stormwater drains.

People needing help with storm damage or with flooding can contact the NSW SES on 132 500.

The Bureau says damaging winds around 65 kmh with peak gusts of 90 kmh may affect the Illawarra and Shoalhaven coastal fringe, particularly during the afternoon and evening. 

Very heavy surf which may lead to localised damage and coastal erosion is forecast for parts of the Illawarra and South Coast forecast districts. 

Beach conditions in these areas could be dangerous and people should stay well away from the surf and surf exposed areas.

Rain is expected to ease to showers by Wednesday morning, according to BOM.