Thunderstorms and torrential rain could be on the cards for Hawke's Bay tonight, with severe weather watches issued for the region by Metservice.

A trough is expected to deliver isolated thunderstorms to central parts of the North Island this evening, accompanied by torrential rain of 25 to 40mm or more per hour.

Such intense rainfall can cause surface and flash flooding, and may lead to slips. Driving conditions can be hazardous.

The trough is expected to weaken this evening but become active again for a time on Wednesday, bringing another period of heavy rain for some areas. A severe weather watch is still in place for the region, set to remain in force until tomorrow afternoon.

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Metservice forecaster Cameron Coutts said the region could expect periods of rain with isolated thunderstorms and possible downpours from 11am today until 3pm Wednesday.

During this time rainfall accumulations could reach 25-50mm, possibly more, in the space of one hour, he said.

"We've got a warm, moist feed coming from the tropics over the upper two thirds of the North Island. There are features within this flow and there's some good upper support for thunderstorms."

During this afternoon and evening thunderstorms from western parts of Auckland across the central high country to inland Hawke's Bay could be accompanied by torrential rain.

Federated Farmers Hawke's Bay president Will Foley said he had never seen the frequency and consistency of thunderstorms in the region before, adding many farmers were treating this period as an early start to autumn.

"The amount of rainfall is not normal for this time of the year and farmers are really happy. They're not stressed out about the climate, no one is short on feed and stock prices are reasonable."

The primary concern for local farmers was facial eczema; the warm and humid weather creating the "perfect storm" for the disease to grow and spread.

Hawke's Bay Fruitgrowers' Association president Lesley Wilson said local growers could do without the excess heat, humidity and rain.

"It makes the whole harvest time harder work. It not affecting fruit quality but it's hard work when you're outside in this humidity. On Monday we knocked people off early because of the heat."

The warm, spring weather had ripened fruit early this year and harvesting had been brought forward to keep up with the fruit, she said.

Rainfall figures from Hawke's Bay Regional Council show the region has already received 84 per cent of it's average rainfall for February; rainfall already exceeding the monthly average in northern parts of the region.

Hawke's Bay Winegrowers Association deputy chairman Xan Harding said short, sharp dumps of rain weren't a problem for grape growers, but extended periods of wet weather could raise difficulties.

"Obviously we had a chunk of wet weather over the weekend but we're still far enough out from the harvest that it's not too problematic for us.

"We're still looking with great interest at what [tropical cyclone] Gita's going to do next week when it comes out of the tropics and comes to visit us."

Mr Harding said there were still several weeks until harvest, which was tracking about seven to ten days ahead.

"We're mostly well away from any kind of trouble but every time we do get these warm periods it makes us more dependant on having good, fine weather later on to dry out."

People in Hawke's Bay were advised to keep up to date with the latest forecasts in case the watches were upgraded to full warnings or new areas were added.

Updated forecasts are available online at metservice.co.nz