Heavy downpours, thunderstorms, chilly temperatures and the chance of small tornadoes are in store for parts of the country, forecasters warn.

It could be a wet start to Wednesday for some areas as nasty weather makes its way across the country.

An area of low pressure is forecast to lie west of central New Zealand tomorrow morning, bringing with it an associated band of rain embedded with thunderstorms that will spread south over the North Island.

While overnight cloud will mean warmer temperatures for northern parts of the North Island, compared with last week, the day is forecast to start with a moderate risk of thunderstorms for Northland and Auckland.

MetService predicts these thunderstorms will produce localised heavy rain in the range of 10 to 25mm/h. There is a low risk one or two severe thunderstorms about Northland will bring downpours of up to 40mm/h.

“The thunderstorms may also bring wind gusts of 80-90km/h, and there is a low risk of one or two small tornadoes about coastal areas,” MetService said.

The risk of thunderstorms spreads further south to affect the Coromandel Peninsula, northern Waikato and coastal Waitomo later in the morning and North Taranaki and western Bay of Plenty towards midday.

MetService meteorologist Mmathapelo Makgabutlane said the-low pressure system will bring “quite a bit of rain” with it, particularly for the eastern Bay of Plenty and top of the South Island.

“Most of the North Island will be seeing some rain and as it continues to drift across the rest of the country, [there will be] a lot of cloud and rain for the top of the South Island as well.”

Heavy rain watches will come into effect for Tasman, about and west of Motueka, for 13 hours from 4am on Wednesday and for eastern Bay of Plenty from 9am. Amounts of rainfall may approach warning criteria.

Meanwhile, temperatures in the top of the North Island will be slightly higher than those seen over the past week, with a high of 20C predicted in Northland and Auckland.

The rest of the North Island will see top temperatures in the mid-to-high teens and the lowest are set to be in the high single digits.

MetService predicts it will be another chilly one for the South Island overnight, with temperatures as low as 2C.

Makgabutlane said the bottom half of the South Island will see “beautiful, clear conditions” throughout Wednesday.