"The windier weather basically removes the chance of frosts for many areas also," Mr Duncan said.
"Overnight lows in the South Island may even be in double digits at times over the next 14 days."
In Auckland, overnight lows are expected to be back into double figures by midweek. During the day, Aucklanders should enjoy highs around 16C by the week's end, Mr Duncan said.
However, the break from the cold is unlikely to last.
"At this stage the computer models suggest the middle of July sees potential for another wintry snap."
The MetService also expects strong northwesterlies to develop over the South Island this week, and says people in the north may want to dust off their umbrellas.
Duty forecaster Richard Finnie said wet weather was predicted for the top half of the North Island this week.
Windy conditions were likely to raise temperatures in the south "and it will probably melt quite a bit of snow in the lower-lying areas of the South Island".
Ski area manager Steve McGill said hundreds of skiers and snowboarders queued at Whakapapa and Turoa for the opening day of their ski seasons at Mt Ruapehu on Saturday.
"There were lots of snow players or people just coming up for a look."
Mr McGill said the forecast over the next week looked reasonably good but lifts on the upper mountain on both skifields remained closed for now.
"The upper mountain is still just one snowstorm away from opening but it's looking good for this time of the year."