Heavy rain could be a 'game-changer'

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Drought-breaking rain is expected to saturate most of the North Island next week, with falls of up to 80mm forecast for some areas.

Climate scientist Dr Jim Salinger said a low pressure system developing in the Tasman Sea north of New Zealand would bring two or three days of heavy rain early next week.

"It could be the weather system that produces a good amount of rain. It's a rain-maker that would certainly produce significant rainfall for the northern half of the North Island,'' Dr Salinger said.

He said farmers should be excited at the prospect that the 50mm-80mm of rain could end drought conditions in some areas.

The days were still long and warm enough that the rain would promote significant grass growth before winter, Dr Salinger said.

"I imagine [farmers] will be delighted," he said.

MetService forecaster Stephen Glassey said it was too early to predict how quickly the weather system would move over New Zealand.

He said it was likely to arrive at the start of next week and bring rain to most of the country.

"Typically these systems that come down from the north Tasman Sea do have the potential to bring heavy rain," he said.

WeatherWatch.co.nz analyst Philip Duncan said the low had the potential to be "a real game-changer" but warned there "are never any guarantees when it comes to the weather".

"Yes, we think a low is likely. Yes, we think it will bring rain to New Zealand. No, we can't say for certain exactly where the heaviest rain will fall at this early stage," Mr Duncan said.

An official drought has been declared for the North Island following one of the driest summers in more than 50 years.