Heavy rain and thunderstorms could strike Auckland and Wellington tonight as our neverending summer takes a few days off.

The stormy weather that's lashed parts of the western South Island is expected to reach further north late this afternoon, bringing with it the chance of small tornadoes.

MetService has issued a severe weather warning for heavy rain, thunderstorms and strong winds over many parts of the west of New Zealand.

Travellers heading to the capital today by plane are being warned flights could be disrupted by bad weather.

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Air New Zealand says strong wind lashing the region may affect flights in and out of Wellington today and for passengers to check arrivals and departures.

Strong winds have already ramped up in the region with the New Zealand Transport Agency issuing a warning for motorists heading over the Rimutaka Hill.

High-sided vehicles and motorcyclists have been advised to take extra care travelling over the summit highway.

Meteorologist Tom Adams said the bands of heavy rain and heavy wind gusts seen around the West Coast and Wellington were forecast to make a repeat appearance over the next seven days.

The thunderstorms would be spreading north over Buller, northwest Nelson, Horowhenua, Kapiti Coast, Taranaki and Western parts of Waitomo and Waikato this afternoon.

MetService said these storms could produce localised rainfall rates of 10-25mm/hr, strong wind gusts of 90-110km/h, and the chance of small tornadoes.

The rain was forecast to be the stormiest today, Wednesday and Friday and in between it would be calmer, though not completely dry.

Mr Adams said it was important for those out and about to be aware as the bad weather would cause already high rivers and streams to rise rapidly and could cause slips and surface flooding around parts of the country.

"This makes it really important to check the forecast and warnings before planning gigs or other activities," he said.

Cooler temperatures were also expected as a cold blast was due to set in late tomorrow.

"Gale force winds will also whistle across the Canterbury Plains, Wairarapa and through Cook Strait and there should be some fresh snow on the tops of the southern peaks."

Weather in the main centres

Auckland

Monday: Few showers, mainly evening, chance of heavy rain and thunderstorms. H: 21C L: 15C.

Tuesday: Early showers, increasing fine breaks. Southwest easing. H: 19C L:12C.

Wellington

Monday: Showers to rain in the evening, chance of heavy rain and thunderstorms. Northwesterly winds rising to gale force. H: 18C L:10C.

Tuesday: Showers with strong southerlies, then clearing and winds easing. H: 14C L: 9C.

Christchurch

Monday: Often cloudy, a few showers. Gale southwest change. H: 20C L: 6C.

Tuesday: Showers clearing morning and southwest gradually dying. H: 13C L: 5C.

Dunedin

Monday: Occasional rain from late morning, gale southwest change. H: 17C L: 7C.

Tuesday: Showers clearing morning, strong southwest dying. H: 11C L: 7C.