Residents in the Bay of Plenty are being warned to prepare for a wet weekend after the MetService issued a severe weather watch with a chance of heavy rain about the eastern ranges.

A strong, moist north-west flow is covering New Zealand ahead of a cold southerly change which is expected to spread northwards tomorrow afternoon.

Heavy rain is forecast for the Eastern Bay of Plenty, while showers are expected in the Western Bay. Photo: MetService.

The MetService says a trough embedded in the flow is currently bringing heavy rain to northern Westland and this will move across the North Island tomorrow.

Heavy rain is expected to hit the Eastern Bay of Plenty ranges, and there is also a chance of showers becoming heavy at times in the Western Bay.

In addition, strong north-to-northwest winds are expected over central New Zealand ahead of the trough.

'There remains uncertainly as to the depth and track of this low, but the heaviest rain is expected about northern and eastern parts of the North Island,” they explain.

'There is moderate confidence that rainfall accumulations will approach warning criteria in Northland, Auckland, eastern Waikato, Coromandel Peninsula, Bay of Plenty, Gisborne and Hawkes Bay on Sunday, and the same confidence of heavy rain for Gisborne, Hawke's Bay, Wairarapa, Wellington and eastern Marlborough on Monday.

'East to south-east winds will likely rise to gale about central parts of New Zealand over the weekend, with a low risk of severe gales for Manawatu to Wellington, the Marlborough Sounds and western parts of Nelson on Sunday and Monday.”