Severe rainfall and potential flooding may hit the Central Coast, Newcastle, Lower Hunter and Manning Rivers from tomorrow morning, according to the Bureau of Meteorology (BOM).
The BOM issued a statement saying the coastal trough was expected to bring rainfall until the end of the week and would be on flood watch.
BOM also monitoring Sydney and Blue Mountains
Sydney, the Blue Mountains and Great Lakes are on the edge "of the worst conditions" and will be monitored, according to state manager Ann Farrell.
Ms Farrell said wet conditions were expected in areas to the east of the Great Dividing Range and the rainfall could become severe in areas between Taree and Wollongong.
"[There] will be some very heavy bursts of rain and while the specific areas of greatest impact are still uncertain, we expect to see this occurring from early morning on Wednesday, with more to come tomorrow night," Ms Farrell said.
"This could be enough to cause road and riverine flooding, and to create dangerous conditions around stormwater drains, along with slippery roads.
"Our primary areas of concern for tomorrow are the Central Coast, Newcastle and Port Stephens areas."
'Clean gutters and downpipes'
NSW SES Commissioner Mark Smethurst urged residents in affected locations to prepare for severe weather.
"A few simple preparations such as cleaning gutters and downpipes and checking your roof is in good repair can make a big difference in reducing potential damage to your property and reducing calls to our volunteers," Commissioner Smethurst said.
"Once severe weather starts, delay non-essential travel, bring pets indoors, park your car under cover, and most importantly, do not drive in floodwater."ABC