Kiwis can expect a wet Tuesday as storms and colder temperatures blow in across the country ahead of a winter blast on the weekend.

Aucklanders will be among those seeking shelter this morning as periods of heavy rain - and even possible thunderstorms - hit the city, until the afternoon brings fine breaks and a top of 20C, MetService says.

The rain should clear tomorrow and Thursday for tops of 19C and 20C, before returning for a wet and wintery Friday and weekend.

Forecaster WeatherWatch is also tipping the weekend's "winter blast" to send temperatures plummeting by up to 10C.

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It could see Auckland's forecast high drop from 20C today to 13C on Saturday, while Hamilton will plunge to a daytime high of 12C.

Hail is also possible in Auckland on Saturday.

Today's morning rain and possible thunderstorms will also hover over much of the top of the country from Whangarei and the Coromandel to Tauranga and Hamilton, which are all tipped to hit highs ranging from 19C-20C.

Wellingtonians can expect only occasional rain and a top of 17C, however, the blustery winds will turn into gales in exposed places.

Napier in the east and New Plymouth in the west are also forecast rain and tops of 18C.

In the South Island, Christchurch and Dunedin residents can expect a high of 17C and "a few spots of rain", while more persistent falls are expected in Blenheim and Queenstown.

Heavy and possible thundery rain is forecast for the West Coast.

Cold and wet week

It comes as MetService's long-range forecast is for stormy, windy weather across most of the country, with colder temperatures and unsettled wet conditions.

MetService meteorologist Lisa Murray said this is a change from the high pressure systems that we have seen for the first half of the year.

"This week is a really good example of it, where we are just getting front after front, but up until now the dominant weather that we've had is high pressure systems.

"So we've had warmer than average temperatures around many parts of the country, and dryer for a lot of areas like Northland, Auckland, Hamilton, New Plymouth and Palmerston North. All of those areas have had a dryer five-month period than they have had in the past five years."

Murray said this week, even though there are fronts moving up the country, northwesterly winds will keep things a little bit warmer than average for this time of year.

"But this weekend, there is going to be a change to a more southerly flow and that is going to bring colder air in so we will see a temperature change and not great weather all around.

"The weather pattern is definitely changing now, and we can expect more disturbed weather - but in between the storminess you will still have reprieves, it is not all doom and gloom."

The first of two significant fronts moving over the nation will arrive midweek and bring rain to most areas, as well as snow to around 1200m for the southern South Island.

Then, towards the weekend as we approach the official start date of winter, cold southwesterlies are set to pack a punch for New Zealand as the second front arrives.

Today's forecast

Whangārei:

Periods of rain, chance heavy with thunderstorms, clearing to fine breaks. High 21C, Low 11C.

Auckland: Periods of rain, heavy with possible thunderstorms, clearing to fine breaks. 20C, 13C.

Tauranga: Drizzle, turning to rain morning, chance heavy with thunderstorms. 20C, 12C.

Hamilton: Periods of rain developing morning, chance heavy with thunderstorms. 19C, 10C.

Rotorua Drizzle, turning to rain morning, chance heavy with thunderstorms. 16C, 10C.

New Plymouth: Periods of rain, chance heavy in squally thunderstorms, easing to showers by evening. 18C, 13C.

Whanganui: Cloudy. Occasional rain from afternoon, clearing at night. 20C, 12C.

Napier: Becoming cloudy. Periods of rain from late morning. 18C, 13C.

Wellington: Cloudy. Occasional rain from late morning. 17C, 13C.

Nelson: Rain developing morning, possibly heavy and thundery from afternoon. 16C, 9C.

Christchurch: High cloud and a few spots of rain. 17C, 7C.

Dunedin: Mostly cloudy. Rain developing in the evening. 17C, 8C.