Summer's here - but fleetingly in Auckland

American singer-songwriter Jack Johnson does his bit at Piha yesterday during the beach clean-up organised by Sustainable Coastlines. Photo / Brett Phibbs

Yesterday may have marked the first day of summer but Auckland's weather will deteriorate as a subtropical low moves toward the country.

MetService duty forecaster Philippa Murdoch said most parts of the country would be fine and sunny today with temperatures in the low to mid 20s until Thursday.

"Overnight temperatures will be fairly mild as well in around about the mid-teens," she said.

While Auckland is also set for a fine day today, cloud will increase tomorrow with a chance of drizzle in the north and east of the region.

"On Wednesday that could turn to rain. We've got northeasterlies strengthening and turning to rain so it'll be warm and humid," Ms Murdoch said.

"That rain continues through to Thursday and then [there] could be a few heavy falls."

The northeasterlies would continue to bring in periods of rain on Friday, Ms Murdoch said.

A low approaching from the north would head down the country tomorrow and Wednesday, affecting the upper North Island north of Taranaki through to the Bay of Plenty and bringing with it high cloud and a few spots of rain, she said.

The South Island is also set for a mainly fine week, with a bit of cloud hanging around early in the week.

"From late Wednesday through to Thursday we'll have some rain spreading into the west of the South Island and also the north - Marlborough, Nelson."

WeatherWatch head weather analyst Philip Duncan said the week ahead may not be quite as hot as last week but it would still be humid with the subtropical system coming down and affecting the upper North Island.

"Summer's definitely here," he said.

One visitor making good use of the weather yesterday was Hawaiian singer-songwriter Jack Johnson, who took part in a clean-up of Piha beach.

Fans were invited to take part in the clean-up yesterday alongside the singer, who performs at Auckland's ASB Theatre tomorrow and on Wednesday.