Auckland is set to see 31 hours of non-stop rain starting this afternoon as the school holidays kick off on a soggy, bleak note.

MetService has this morning extended its heavy rain warnings and watches with many North Island northern and eastern regions set to be drenched by a tropically-fuelled Tasman rainmaker.

Holiday hotspots Northland, Auckland and Coromandel Peninsula are all in line for more than a day's worth of rain, while Bay of Plenty could expect to see even more downpours over the weekend.

Periods of heavy rain are set to start falling in the coming hour and not let up until Saturday 8pm, with rainfall amounts threatening to approach warning criteria.

MetService says eastern regions can expect between 110-170 mm of rain with the biggest cloudbursts falling in the ranges east of Whakatane.

It says the heavy rain might cause streams and rivers to rise rapidly with a possibility of flooding and slips and hazardous driving conditions.

And while the alert extends to 1pm Saturday it warns further bursts of heavy rain might affect this area late Saturday and overnight Saturday.

Thames-Coromandel District Council has issued a warning to motorists telling those travelling into the holiday region up to 130mm of rain and gusty winds was expected to hammer the region from 3am Saturday through to 6am Sunday.

"With our catchments still saturated, it is possible that more slips and surface flooding will occur," it posted on Facebook today.

While wet weather is in store for most of the North Island the South Island will enjoy a spell of dry weather in most parts.

However, MetService is warning the school holidays will have a wintry feel for the south with polar air straight off the Antarctic shelf lingering across much of the country this weekend and into next week with another "bitter outbreak" signalled for Wednesday.

"Current models suggest the cold air moving over the country mid next week has Antarctic origins," the forecaster posted on Facebook.

By Thursday temperatures for most main centres are expected to plummet to single digits with Wellington recording a low of 4C and a high of 9C, while Christchurch is expected to get down to near-freezing on 1C overnight and 10C during the day.

The forecaster said the current model trajectory had the air off Antarctica moving quickly across our shores.