"Tomorrow we have a few places who will be a few degrees above normal," James said.
"We are looking at highs of 20C for Masterton and Blenheim, so that's ahead of that front that's coming up - reasonably strong north-westerly winds usually do bring warmer air."
The West Coast of the South Island is expected to bear the brunt of the approaching front with heavy rain on Monday.
Rain is expected to reach Tararua Range, Mount Taranaki and the ranges of eastern Bay of Plenty and Gisborne on Tuesday.
It is also forecast to reach Auckland on Tuesday.
Main centre forecasts today
Whangārei
Fine. Southeasterly breezes. High 17C, low 7C
Auckland
Fine. Southwesterlies. High 17C, 8C
Hamilton
Fine. Southwesterly breezes. High 17C, 2C
Tauranga
Fine with light winds. High 17C, 6C
Wellington
Fine. Light winds, northerlies developing evening. High 14C, 7C
Christchurch
Fine with low cloud tonight. Northeast breezes. High 16C, 5C
Dunedin
Fine apart from some cloud late evening. Light winds. High 13C, 6C
Source: MetService