Auckland rush-hour motorists will be battered by strong winds and gales on their commute home as thundery westerlies hit parts of the North Island.

Metservice meteorologist Sarah Haddon told the Herald the Harbour bridge has already had gusts up to 80km/h with a mean wind speed of 55km/h.

Elevated and highly exposed parts of Auckland have had gusts reach 95km/h and has recorded a mean speed of 70km/h.

The NZ Transport Agency is warning motorists to take extra care crossing the Auckland Harbour Bridge, with some gusts expected to reach 100km/h.

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Heavy traffic has built up on the Northern Motorway heading northbound between Northcote Rd and the Upper Harbour Highway.

Meanwhile, traffic heading citybound on the Northern Motorway is heavy between Esmonde Rd and the Harbour bridge.

Haddon said wind speeds and gusts will be at their fastest from 4.30pm onwards.

"It will be windy for the most part of this evening and then just taper off a little bit overnight but still some strong southwesterlies for most of tomorrow," she said.

Commuters using the Southern and Onehunga railway lines should expect disruptions due to a track fault at Penrose, Auckland Transport warns.

Traffic is heavy on the Southern Motorway heading southbound at Manukau and at Takanini. Traffic is heavy heading citybound between Mt Wellington and Greenlane.

The Northwestern Motorway is heavy between Great North Rd and Lincoln Rd.

Traffic heading northbound on the Southwestern Motorway is heavy between Bader Dr and Neilson St and southbound traffic is heavy at Massey Rd and approaching the Southern link.

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Severe weather watches are in place with strong westerlies expected to spread over the North Island, then slowly ease on Wednesday.

This watch covers the possibility of westerly winds approaching severe gales in exposed parts of Auckland, Coromandel Peninsula, Waikato and Bay of Plenty west of Te Puke.

In addition, periods of heavy rain are expected about south Taranaki, Whanganui, Taihape and parts of Manawatu north of Palmerston North tonight and tomorrow morning, also about northwest Nelson until this afternoon.

There is a moderate risk of thunderstorms from western Waikato down to North Taranaki later this morning and afternoon and about South Taranaki and Whanganui later this afternoon and evening.

These thunderstorms are likely to produce localised heavy rain and small hail.

Another front is forecast to approach Northland tonight, bringing a moderate risk of thunderstorms to western parts of Northland towards midnight.

These thunderstorms could also produce localised heavy rain and small hail as well as strong wind gusts around 100km/h.

The South Island doesn't escape the wet weather during Tuesday, with scattered rain becoming widespread for the lower parts of the Island.

Wednesday will see showery southwesterlies for the North Island and a brief ridge of high pressure builds over the South Island.

Most parts of the South Island will take a break from the wet weather on Wednesday with the showers over the North Island easing in the evening.

Northwesterly winds pick up over the lower South Island early on Thursday ahead of another frontal feature approaching from the Tasman Sea.

This active feature will bring rain and possibly heavy falls to western areas as the front moves north.