Greymouth, Wellington and the western area from Taranaki to Northland would all be getting "a few little showers' throughout the day clearing as it wore on.
"They will stick around Northland and Auckland a little longer - mostly in the west and really light anyway."
In Hawke's Bay, Gisborne, and the Bay of Plenty the day was sunny already and expected to stay sunny for the rest of the day.
Tauranga and Whakatane were expected to be the warmest spots in the North Island, hitting 24C and 25C respectively.
Wanaka was also looking at similar temperatures, Flynn said.
For most other spots the high would be in the late teens or early twenties.
"Nelson's looking pretty nice at the moment as well, and is expected to stay pretty sunny all day."
Today's forecast
Whangarei: Long fine spells. Southwesterlies. High 22C Low 15C
Auckland: Fine and cloudy periods, chance of a light shower. Southwesterly. High 21C Low 15C
Hamilton: Morning cloud, chance of shower, then mainly fine. Southwesterly. High 21C Low 9C
Tauranga: Some morning cloud, otherwise fine. Southwesterlies.High 24C Low 13C
New Plymouth: Morning cloud, chance of shower, then mainly fine. Southwesterly. High 19C Low 9C
Napier: Fine. Cloud increasing afternoon. Light winds. High 22C 14C
Wellington: Cloudy periods, early drizzle. Light southerly change. High 18C 11C
Nelson: Fine. Light winds, afternoon sea breezes. High 21C Low 13C
Christchurch: Cloudy periods, chance of light morning shower. Southerly develops. High 17C Low 10C
Wanaka: Fine, apart from some morning cloud. Light winds. High 25C Low 10C
Dunedin: Cloudy periods. Southwesterlies. High 17C Low 9C