Because the complex is slow moving, it could reach the region early next week and there is a low chance of heavy rain.
MetService would continue to keep an eye on the complex low, he said.
"It's fairly unpredictable but we will monitor it."
These systems are normal for this time of year and can be experienced all year round, Mason said.
Overnight temperatures are set to warm up.
Most of the week had been dropping to as low as 4C or 5C, but last night was 12, tonight is set for 13, tomorrow 14 and Monday 13.
The rest of the week's lows will be 8C to 10C.
Highs will be similar to earlier in the week, about 18C to 20C.
"It will be quite warm and humid at times."
On Tuesday, a ridge of high pressure should move from the South Island onto central New Zealand and on Wednesday a strong southerly is forecast to sweep up the east coast.
Gales could affect exposed coastal parts of Gisborne and Hawke's Bay, but at this stage they are not likely to become severe.