The Bureau of Meteorology has issued flood watch alerts, with eyes on a deepening east coast low brooding off the New South Wales coast.

The State Emergency Service is on alert from the mid-north coast down to the Illawarra. The SES is asking people to make sure storm drains are clear, and to park cars undercover if possible. The Weather Bureau says a large low pressure system is due to develop over the next 24 hours, bring heavy rainfall and gale force winds. There are flood watch alerts , with a greater than 70 per cent chance of flooding for the Nepean, Georges, Wyong and Paterson and Williams Rivers. A king tide could cause flooding in tidal zones of the Cooks and Woronora Rivers. The rain is expected to increase from late Sunday.