An active weather system will cool down the high overnight temperatures New Zealand has seen throughout the country this past week.

The ridge of high pressure responsible for boosting the mercury level is moving east of the country and will make way for the northbound weather system.

MetSerivce meteorologist Mark Bowe said the active frontal system has been moving over the South Island and will move on to the North Island overnight.

"The southwest change will cool temperatures down a little as the wet weather moves across the country today and into early next week," he said.

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"Many people have had warm and muggy nights but that should come to an end as this week concludes."

Major centres in the North Island like Auckland and Wellington have seen temperatures skyrocket at night, causing rough sleeping for many.

However, those in the North Island will be able to sleep easy this week knowing the weeks of sunny, dry weather will come to an end this week.

Wet weather is expected throughout the coming week, particularly for the North Island, and Bowe said there is plenty to watch out for.

The front will move further north over Sunday night and into Monday morning, with a low risk of isolated thunderstorms as well.

MetService said any thunderstorms which occur have the potential to bring localised heavy rain of 10 to 25mm per hour.

A cool change from the high temperatures is also experienced throughout the country, especially to those in eastern parts of the North Island.

"Napier got to 33C on Saturday which is very close to the highest January temperature on record for that area," Bowe said.

MetService is also forecasting a low-pressure system to lie to the northeast of the country which will affect those in Gisborne and Hawke's Bay.

A moist southwest flow is tipped to brush through the region on Tuesday, Wednesday and Thursday due to the upset weather system.

Conditions in the South Island should improve after the nasty front slides northwards with a front with a narrow ridge trucking behind.

The ridge should keep all of the wet weather confined to the North Island, Metservice said.

Monday's forecast

Whangarei:

Brief rain late morning, then a few showers. Northwesterlies changing southwest late morning. High 24C, Low 14C.

Auckland: Brief rain about mid-morning, then a few showers, chance heavy and thundery. Northwesterlies changing southwest morning. 22C, 14C.

Tauranga: Brief rain around midday, then a few showers, chance heavy and thundery. Northwesterlies dying out by early afternoon. 21C, 14C.

Hamilton: Morning rain, then a few showers, chance heavy and thundery. Northwesterlies change southwest. 21C, 10C.

Napier: A period of morning rain then a few showers, chance heavy and thundery. Winds becoming light. 23C, 15C.

New Plymouth: Rain before dawn then a few showers and fine spells. Westerlies changing southerly afternoon. 20C, 13C.

Wellington: Mostly cloudy, a few showers. Southerlies becoming strong. 19C, 14C.

Nelson: Partly cloudy, and a shower or two after midday. Light winds. 20C, 12C.

Greymouth: Early showers, then becoming fine. Southwest breezes from evening. 21C, 11C.

Christchurch: Showers clearing afternoon and fresh southwesterly easing, but cloud and drizzle again evening. 17C, 11C.

Queenstown: Early showers clearing, then fine apart from evening cloud. Southwest breezes, dying evening. 21C, 8C.

Dunedin: Showers clearing early morning, then fine apart from evening cloud. Fresh southwesterlies easing. 18C, 11C.

Invercargill: Cloudy periods, and a light shower or two until evening. Southwest breezes. 17C, 9C.