Update: The very heavy rainfall anticipated is not being consistently predicted on the current models for today. It seems that with ample moisture, rain totals of up to 10-15mm of rain is likely in some areas although GFS still has heavier rainfall possible in the Hunter Valley.
A localised very heavy rainfall event seems now more and more likely to occur from just north of Sydney Central Coast to the lower Hunter Valley. Both models GFS and the Bureau Access R models are placing high precipitation of up to at least 80mm in this region.
The storms may develop rapidly in the afternoon as very moist tropical air combines with surface heating in a possible region of convergence creating instability. Early in the afternoon, the rain event may be northwest of this region in a narrow band in the North West Slopes. The system then centres on the lower and southern Hunter Valley regions about early evening and after sunset. Given there has been at least some rain in these areas on Sunday, any further rain may cause localised flash flooding.