The Bureau of Meteorology warns a trough moving across NSW could prolong flooding, with widespread showers and thunderstorms predicted across much of the state, especially on Tuesday.
Communities are bracing for more destructive rain as the bureau issued minor to major flood warnings in a number of catchments.
The forecaster on Monday afternoon warned the low pressure system may also move over the southern coast on Wednesday.
"We're seeing quite a lot of cloud streaming through western NSW at the moment," bureau senior meteorologist Jane Golding said.
"That will produce some generally wet and stormy conditions across NSW for the next few days," she said.
Severe storms could form and threaten heavy rainfall in a short period of time, which could lead to flash flooding in some areas.
"Storms by their nature, they're pretty hit and miss so not everywhere," Ms Golding said.
Damaging wind gusts of up to 90km/h are possible, and with many catchments already saturated they could bring down trees quite easily, Ms Golding said.
In the state's central northwest, the towns of Warren and Wee Waa are expected to remain isolated for days as the flood emergency continues.
Further east, the town of Gunnedah continues to be affected by flooding but the water is slowly receding.
The Namoi River, which runs through Gunnedah, peaked at 8.24 metres at the weekend. SES workers are assessing the damage.
The latest floods claimed the life of a five-year-old boy who was found dead on Saturday afternoon after the vehicle he was in was swept away at Tullamore, near Parkes.
Emergency services received hundreds of calls for help since flooding hit the region last week.
SES Assistant Commissioner Nicole Hogan said Central West and North West regions remained at risk of further flooding during the next six to eight weeks.
With more rain forecast this week, Ms Hogan said it was crucial that residents and those travelling in the region took care.
"We are asking people, particularly with the school holidays, to prepare their route, (and) know where they're going ahead of time ... and if they are camping on the side of a river, to really be aware of their surroundings," she told ABC TV on Monday.
"Communities just really need to understand their flood risk, know what the conditions are like, be aware of their surroundings."
Ms Golding said Wednesday will be the wettest day on the South Cost while Sydney faces a deluge on Thursday.
"Expect showers to continue through to the weekend but not as heavy and widespread as mid-this week," Ms Golding said.
On the north coast at Lismore, which was devastated by floods earlier this year, Labor leader Chris Minns said the community's key message was that promised support must hit the ground.
Lismore was submerged in the record-breaking floods of February and March before coming under renewed threat last week from saturated catchments.
"The funds need to come, if they don't come you'll start to see businesses shut their doors and they won't return," Mr Minns said.
