The south and west of the South Island would also be showery, moving northwards to Kaikoura tonight.
"Most of Marlbourough and Nelson should be staying dry," Flynn said.
Temperatures will rise to a scorching 25C in Hastings, Kerikeri and Pahia. So a beach day could be on the cards for holiday makers in the north and east of the North Island.
Most of the rest of the North Island will get "average" temperature highs in the low to mid twenties.
But the South Island would be cooler than average for this time of year. It would be particularly chilly in Southland and Gore, where temperatures would only reach 13C and 12C respectively, Flynn said.
Tomorrow's forecast was "looking similar" with patchy cloud in the North Island and showers in the south and west of the South Island. Kaikoura would get a spot of rain tomorrow morning, before clearing to a mostly fine day.
Today's forecast
• Whangarei: Mostly sunny, south west breezes easing, high of 24C
• Auckland: Morning cloud and the chance of a shower, but a mostly sunny afternoon, 21C
• Hamilton: Morning shower possible, then fine spells increasing, southwesterly wind, 22C
• Tauranga: Mostly fine day except for some morning and evening cloud, 24C
• Wellington: Fine spells, northerly change later today, 18C
• Christchurch: Cloud periods and late afternoon showers, northeasterly developing, 18C
• Dunedin: Cloudy periods, showers, southwesterlies, 14C