Kiwis are in for a warm and wet first week of summer as a humid weather system hangs over the country.

Its tentacles are well and truly wrapped around Auckland, which will have a few days of showers, cloud and humidity.

"We've got a warm, moist north-westerly flow that's keeping us warm," MetService meteorologist Emma Blades said.

"Temperatures for Auckland are pretty average for this time of the year. We have low-20s for the maximums all week."

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The forecast was pretty identical for every day from today until Friday and Aucklanders staring out of their office windows will see plenty of grey.

Overnight it will be warm, with the temperature hovering around the high teens in the wee small hours.

"It's one of the cloudiest areas this week. Other areas are much better," Mrs Blades said of Auckland and surrounding areas.

The week's heaviest rain is expected in Buller and Fiordland, but in a blow for parched farms, eastern areas will be drier.

The warmest parts of the country will be Central Otago and South and Mid Canterbury, with Alexandra expected to hit 30C.

In the North Island, Palmerston North could reach 26C today, while the Hutt Valley in Wellington will be just one degree below that.

The capital itself is in for a stunner today, but the wind will return tomorrow after a few days' reprieve.

Meanwhile, further afield, tropical cyclone Tuni has changed course and will miss Niue. However, it will pass sooner than expected, about midday today.

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Today's outlook
Northland: Cloudy periods and the odd shower and a high of 21C.
Auckland: Showers develop, 22C.
Waikato: Fine at first then becoming cloudy with showers with a high of 22C.
Bay of Plenty: Fine at first then cloudy with showers and a high of 20C.
Wellington: Fine, 21C.