New Zealanders won't just be staying home but staying indoors as cold weather arrives over most of the country this week.

Temperatures are expected to drop as New Zealand starts its fourth week of a national lockdown, with parts of the South Island falling as low as 1C tonight

"We'll have some very cold temperatures for Christchurch, Alexandra and Wanaka," said Metservice duty forecaster Sonya Farmer.

A southwesterly flow which brought thunderstorms and hail to the South Island yesterday is expected to continue over the next two or three days.

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"It will probably keep a few people inside because it won't be very palatable," said Farmer.

Further thunderstorms are possible this morning in Buller, Fiordland, and Southland. There is a slight chance of thunderstorms about coastal parts of the South Island, Taranaki, Whanganui, Manawatu and Wairarapa.

The rest of the country could expect "cold, wintry" conditions and showers, Farmer said.

Auckland will cool off to around 18C during the day and fall to 13C at night this week. It will also get showers throughout the week and possibly rain this weekend.

There is chance of heavier rain in Buller, Westland north of Hokitika, Tararua Ranges, Taranaki and the King Country during Friday and Saturday.

Strong winds yesterday prompted transport authorities to warn about travel across Auckland's Harbour Bridge. In the central North Island, winds gusted as high as 120km/h.