After significant totals over the last few days in the northeast of NSW, heavy rain during Sunday will possibly lead to flooding.

A very humid airmass is lingering over NSW thanks to northerly winds bringing tropical moisture. This warm and moisture-laden air will interact with a strong cold front crossing the southern states and a broad trough extending from the NT to the southeast of Australia. As a result, a rain band that is sweeping through SA, Victoria, and Tasmania during Saturday will consolidate and affect much of NSW on Sunday.

Rain will develop in the southern districts from Saturday evening and move gradually northeast, arriving in the Sydney region early morning on Sunday. Isolated thunderstorms, embedded in the rain are possible although they are more likely on the leading edge of the rain band. 

Image: Forecast accumulated 24-hour rain to Sunday evening according to the ECMWF-HRES model.

The heaviest rain is expected across the Hunter, Mid North Coast, Northwest Slopes, Northern Tablelands, and Northern Rivers during the afternoon. These areas also have a good chance of seeing severe thunderstorms, which may result in flash flooding.

Most models suggest widespread falls of 20-50mm in 24 hours across the northeastern districts, although localised heavier falls exceeding 100mm are possible. The Sydney region could see 24-hour totals of 15-30mm, with the most significant rain over northern and western parts of the basin.

The system will keep moving further north causing rain to ease in the evening for most places, being confined to the far northeast, where it is likely to continue during Monday.

A Flood Watch for several catchments across the North West Slopes and parts of the Northern Coast is currently in place. You can keep track of the latest weather warnings issued here.