The Bureau of Meteorology warns that dangerous thunderstorms have been detected on the weather radar near Somersby, Dooralong, Mangrove Mountain and the Watagan Mountains west of Cooranbong.
Areas likely to be affected are Wyong Tuggerah, Berkely Vale and Warnervale by 3.55pm, Maitland Belmont, Cessnock and Swansea by 4.25pm.
