A scorching day is forecast for much of the North Island, and central and eastern regions are due for a thundery start to the weekend.

Auckland and Whangarei can expect temperatures soar to 28C today, plus fine skies paired with light winds.

Tauranga and Hamilton are in for a toasty high of 25C and temperatures would peak at just 20C in the capital.

Wellington and Palmerston North are in for a smattering of rain heading into the afternoon.

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Warm temperatures in the north follow an unusually hot night - Tauranga was 21C at 2am.

Temperatures had already hit 20C at 7am in Auckland.

Gisborne and the East Coast can expect more volatile weather today.

Metservice is warning of a high risk of thunderstorms for the area this afternoon and into the evening.

Stormy weather may also hit Bay of Plenty, Taupo and Taihape during the afternoon and evening.

The storms are expected to produce heavy rain and hail and could become severe, producing heavy, localised downpours.

However, the weekend forecast is better. A mix of sun and cloud is expected in Gisborne and Napier tomorrow and Sunday.

MetService forecaster Cameron Coutts says another cold front is forming in the Tasman Sea and is likely to hit much of New Zealand from about Wednesday next week.

"There could be some reasonable rain in the northwest and west of the South Island and also in the north of the North Island - Northland, Auckland, Bay of Plenty and possibly North Taranaki," he says.

"In general for January we think it's going to be slightly above normal rainfall for the west and north of the country but slightly drier in the east."

Thames-Coromandel, which was hit with some of the worst flooding in last week's storm, is forecast to get occasional rain on Tuesday and significant rain on Wednesday.

Auckland can expect occasional rain on Tuesday and showers from Wednesday through Friday next week.

Meanwhile, many West Coast residents will be waking up to soggy backyards this morning after heavy downpours caused flooding - and the weather woes aren't quite over yet.

Stints of torrential rain over the central and northern parts of the South Island yesterday caused surface flooding in Greymouth and Hokitika.

Residents reported flooded backyards and streets transformed into rivers. A welfare centre was set up in case anyone was displaced by the flooding.

Westland Mayor Bruce Smith told the Herald last night rain was "absolutely hosing down" in Hokitika and water levels were not expected to peak until 4am.

Today's forecast for Greymouth and Hokitika was for rain, possibly heavy, easing to showers by afternoon.

A Metservice weather warning said the low pressure system that had caused flooding in central and northern parts of the South Island would stick around until Saturday.

The system created outbreaks of heavy rain in Westland and Buller and the Canterbury High Country over the past day.

Although the heaviest of the rain was over, this area was in for a wet weekend - and the rain looks set to stick around well into next week.

Heavy rain was also forecast to set in over Nelson towards midday today and a severe weather warning is in place from noon until midday tomorrow.

The stints of torrential rain raised the water level of Sawyers Creek in Grey District and Mayor Tony Kokshoorn said it was at an "extremely high level" yesterday evening.

Several streets remain closed in Greymouth and Hokitika and Kokshoorn said about 12 families have had to leave their homes in Greymouth. They are staying with friends and relatives.

In Christchurch, stormwater grates were checked and temporary pumps prepared for the onslaught of rain.

The city missed the worst of the rain, but the low pressure system was also making for a wet end to the week for Cantabrians.

Heavy rain would ease to showers this morning and an overcast day was expected over the region.

The wet weather cancelled the city's Outdoor Cinema screening last night, though it looked set to go ahead this evening.