Parts of New Zealand being battered by heavy rain today are expected to be hit again later in the week.

MetService has issued an "orange" heavy rain warning for the headwaters of Otago lakes and rivers for today, and says the amount of rain could cause streams and rivers to rise rapidly, surface flooding, slips and dangerous driving conditions.

Between 11am and 4pm today between 60mm to 100mm of rain was expected to accumulate near the main divide and 40mm to 80mm within 15km east of the divide.

Heavy rain warnings were also in place for parts of Westland and Fiordland.

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Kinloch Rd near Glenorchy has been closed due to flooding.

Cold and wet week

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."

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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.

Warnings for periods of heavy rain have been issued for northern and western areas of the South Island from today.

The ranges of Westland between Harihari and Otira should expect 100 to 200mm from 4pm today until 11pm tomorrow.

Westland from Harihari southwards should expect 210 to 250mm to fall up until 4pm today, while the headwaters of the Otago lakes and rivers will get 60 to 100mm of rain in the same period.

Fiordland also has a warning for heavy falls for today and Tuesday, as well as a moderate risk of thunderstorms.

Periods of heavy rain are expected in these regions again on Wednesday and continue through to early Friday.

In the North Island today, there is a low risk of thunderstorms about the east of Northland and Auckland and about the north of the Coromandel Peninsula.

The risk area expands to cover the rest of Northland, Auckland, Coromandel Peninsula as well as Waikato and Bay of Plenty during the afternoon and evening.

Though the heavy rain remains confined to the west of the South Island today, most of the country won't be lucky enough to escape at least a period of rain tomorrow as a second front rolls in from the northwest.

Heavy falls, thunderstorms and strong gusts are expected over western regions from Waitomo southwards.

Northern regions about the Bay of Plenty to Northland will also see a burst of heavy rain, while localised areas over Nelson, Marlborough Sounds, Kapiti and Taranaki have the potential to see downpours in squally thunderstorms.

Strong or gale north to northwest winds are also forecast to hit Taranaki, Wellington and Wairarapa.

Though I would like to say that the weather is looking to take a settled turn into the long weekend not only does the turbulent weather remain but also has a bit more of a sting to it with temperatures are expected to drop from Saturday ... just in time for the first day of winter!