But the system will move fast - reaching Northland by the evening - and rain is unlikely to bring any drought relief, except in localised areas affected by thunderstorms.
Thunderstorms are possible this morning in Nelson, Buller, Taranaki and Whanganui, while Kapiti, Horowhenua, Manawatu, Taihape, Taupo, Taumaranui and Waitomo could hear thunder before lunchtime.
In the afternoon western areas from Taumaranui to Auckland are at moderate risk of thunderstorms, while the early evening could see thunder from Taupo across to Gisborne and Hawkes Bay.
There is a low risk some storms could become severe, the MetService said.
Later this week more fronts will bring rainfall to the southwest and cause temperatures to "yoyo", they said.
Christchurch was forecast to bounce from 19C today to 26C tomorrow, 19C on Wednesday and 29C on Thursday.
"As fronts make inroads onto New Zealand we can expect more variable weather conditions", meteorologist Tom Adams said.
"The biggest fluctuations between cool and hot, wet and dry, will be in the south. Further north the fronts will have weakened, but we still expect the coming weather to be more changeable than during the last few weeks.
"With the holidays approaching and people starting to make outdoor plans, it is worth remembering that the weather does change, and it always pays to keep an eye on the latest forecasts. Don't take fine weather for granted."
MONDAY'S FORECAST
WHANGAREI Showers, afternoon southwesterlies. High 26C, Overnight 17C
AUCKLAND Afternoon showers, chance of thunderstorm. High 25C, Overnight 17C
TAURANGA Cloudy, showers from afternoon. High 26C, Overnight 15C
HAMILTON Rain, possible thunderstorms in afternoon, clearing. High 25C, Overnight 13C
NAPIER Rain from midday, easing evening. High 26C, Overnight 12C
WELLINGTON Morning rain then fine. Northerlies turn strong southerly. High 19C, Overnight 11C
CHRISTCHURCH Early rain clearing. High 19C, Overnight 9C
DUNEDIN Fine. High 16C, Overnight 11C
QUEENSTOWN Fine, chance of showers in afternoon. High 21C, Overnight 10C