Rainy, thundery day no biggie: Expert

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A severe-weather watch for Northland isn't cause for concern because patchy rain and isolated thunderstorms are all that will be experienced this afternoon, a weather analyst says.

A low, moving east over the Tasman Sea, is forecast to spread a band of rain southward over the upper North Island and South Island this afternoon, heading into tomorrow morning.

The MetService said that 70mm of rainfall or more in 12 hours would possibly be delivered to areas around Northland, Auckland, the Coromandel Peninsula and the western Bay of Plenty.

It has advised people in affected areas to stay up to date with the latest forecasts in case of an upgrade to a warning.

But WeatherWatch head analyst Philip Duncan said the coming change in weather was unlikely to threaten the North too much.

"It's quite a large but non-aggressive low in the Tasman Sea and a heavy downpour is likely during the middle of the afternoon," Mr Duncan said.

"There are sub-tropical elements in this low."

Although people in low-lying areas weren't threatened by flash flooding, they needed to be aware of Mother Nature.

He said Northland should expect mild weather in the next 10 days.

He tipped highs of 16C to 17C and overnight lows of 10C.

Tomorrow could be a particularly warm day with temperatures about 18C, as the wind's direction changed from northerly to southerly, Mr Duncan said.

"Tomorrow, and particularly Wednesday, should be warmer than average and Friday should be cooler than average.

"After that, it should be average."

Clear skies are predicted for Saturday, Sunday and Monday in most parts of Northland, before showers return on the Tuesday.