A blast of cool air from the south has led to a drop in temperatures and is bringing gales to exposed parts of the country.

MetService meteorologist Kyle Lee said a "disturbed westerly flow" was covering New Zealand on Wednesday, with isolated showers and some thunderstorms forecast.

Auckland would have showers from this afternoon and a high of 19C. There was also a low risk of thunderstorms on the North Island west coast from Wellington to southern Auckland.

There was a moderate risk of thunderstorms associated about Buller, western Nelson (including Kahurangi National Park), the Marlborough Sounds, Horowhenua and Kāpiti Coast and the South Taranaki Bight before dawn, and about Taranaki shortly after dawn.

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There was also a lower risk of thunderstorms across the remainder of Nelson and western Marlborough.

Lee said a front embedded in the flow would see strong winds about the South Island's east coast from Canterbury to Southland.

There was a strong wind warning in place for coastal Clutha and Southland with west to southwest gales up to 120km/h until 7pm, and up to 140km/h on Stewart Island until 5pm.

Lee said the strong westerlies would continue into Thursday, with exposed areas seeing some rain, including the North Island west coast and southern parts of the South Island.

Gales would continue for Southland, Clutha and the Otago Peninsula on Thursday, before easing through to Sunday.

Lee said a ridge would move over the country from the Tasman Sea on Friday with the winds easing off.

Today's weather

Whangārei

Showers developing this morning. Afternoon southwest change. 20C high, 13C overnight.

Auckland

Showers, more likely this afternoon. Southwest change. 19C high, 15C overnight.

Hamilton

Showers, chance heavy, then few and far between after midday. Fresh westerlies. 18C high, 12C overnight.

Tauranga

Cloudy at times. A shower or two this afternoon. Fresh westerlies. 19C high, 13C overnight.

New Plymouth Showers, mainly this morning and could be heavy and thundery. Fresh westerlies. 18C high, 13C overnight.

Napier Fine, morning high cloud. Fresh northwesterlies. 22C high, 12C overnight.

Whanganui Showers, becoming few and far between by mid-morning. Strong westerlies. 18C high, 14C overnight.

Wellington Fine, afternoon high cloud. Northwesterlies, strong in exposed places. 17C high, 11C overnight.

Nelson Fine morning, cloudy afternoon. Southwest breezes. 17C high, 10C overnight.

Christchurch Fine, with high cloud until afternoon. Westerlies. 19C high, 4C overnight.

Dunedin Cloudy periods. Few afternoon showers. Southwesterlies, becoming strong around midday and gusting 110km​/​h for a time. 16C high, 8C overnight.