It's rain, rain, and more rain for most spots around the country as we head into the weekend.

A heavy rain warning was issued for Westland today and Metservice said a low pressure system was expected to bring heavy downpours to the north and west of the South Island.

Meteorologist April Clark said western areas could expect a prolonged bout of rain although spots on the east coast like Christchurch would be a little dryer.

"Eastern areas don't escape altogether, though rain there is expected to be short-lived."

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South Islanders were being warned of the risk of streams and rivers rising rapidly, surface flooding and slips.

Temperatures around the island were cooler than at the start of the week, when a miniature heatwave almost broke records in Invercargill.

Blenheim and Dunedin are on about 21C. Cantabrians will have a rather summery Friday with a high of 25, though this would drop down to around 22C for the weekend.

The North Island was also due for a soaking from today.

Whangarei, Auckland and Tauranga were all forecast to be hit by the downpour, which was expected to last until the start of next week.

The wet weather was paired with mellow temperatures around 20C for these areas.

The weekend was looking similarly damp for Taupo and Wellington, though temperatures were a touch nippier - sitting around 17C.