"In winter you don't normally get westerlies blowing for a whole week.
"Usually it swings around to the south at one point, but it looks as though this is the weather pattern for the next several days."
Although it would be warmer than usual, the weather was also likely to be windy, Mr Duncan said.
"There could be some severe gale warnings issued this week for central and eastern parts of the country."
In Auckland, people could look forward to a break from last week's downpours, with a high of 17C and a mix of sun and cloud tomorrow.
"Things are looking pretty good for Auckland," Mr Duncan said.
"There maybe a little bit of shower, maybe, but it's going to be a mainly dry day."
Monday was also shaping up nicely in the capital, with mainly sunny weather.
Christchurch should also be mild, Mr Duncan said.
"It might be a bit cold in the morning - there could be a frost for some sheltered areas, and then a mostly sunny day."
MetService meteorologist Stephen Glassey also predicted a mild start to the week for the country's main centres.
"It's going to be lots of fine weather for most of the main centres tomorrow," he said.
The MetService was forecasting a front approaching from the Tasman Sea, which would move on to the country on Tuesday, starting in the South Island.
"It's got a very strong northwest flow associated with it, so what it's going to mean is very heavy rain in the west and very strong winds in the east.
"The east of the South Island is going to get some very strong winds on Tuesday, and Wellington and the Wairarapa as well."
As the front moved up the North Island, more rain could be expected, Mr Glassey said.
Temperatures should be relatively warm, however.
