Residents across eastern NSW have been warned to batten down ahead of damaging thunderstorms on the way on Monday afternoon.

The Bureau of Meteorology issued an initial severe thunderstorm warning for parts of the northern rivers, mid-north coast, and northern tablelands.

It was followed shortly after by another “for damaging winds and large hailstones” in areas such as Grafton, Kempsey, Armidale, Tenterfield, Glen Innies and Dorrigo.

“A trough combined with a hot unstable airmass [is likely] to trigger thunderstorms in the north-east this afternoon,” the BOM said.

“Severe thunderstorms are likely to produce damaging winds and large hailstones in the warning area over the next several hours.”

By 3pm (AEDT), Port Macquarie, Nambucca and Coffs Harbour were added to the list.

The BOM said warning areas were likely to continue to expand throughout the afternoon.

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The warning came almost exactly a year after floods devastated Lismore and other towns in the NSW northern rivers. Monday’s wild weather is unlikely to bring such heavy rain, although there are warnings of “supercell thunderstorms”, most likely for mid-north coast and Hunter regions.

Weatherzone forecaster Joel Pippard said warmth, humidity and instability would all collide along the ranges as a southerly change made its way up the NSW coast.

“Upper cold air will be crossing along with the southerly change, allowing for thunderstorms to become severe with large hail, damaging wind gusts and heavy rainfall,” he said.

He said supercell storms could produce giant hail (larger than cricket balls), destructive winds (exceeding 120km/h) and intense rainfall (flash-flooding).

Mr Pippard said thunderstorms looked to be confined generally to on and east of the ranges, north of about Nowra. Sydney, Wollongong and Newcastle might also be in the firing line.