A westerly airflow lies over New Zealand today, a cold front within this flow slowly slides northwards over the South Island during the day.

Northland, Auckland, Waikato & Bay Of Plenty
Partly cloudy, risk of a shower or two from afternoon as light winds pick up from the west. The Bay Of Plenty is mostly sunny, some cloud from afternoon.
Highs: 14-18

Western North Island (including Central North Island)
Cloudy areas develop in the morning, risk of a shower or two from afternoon as west to northwesterly winds freshen.
Highs: 10-17

Eastern North Island
Mainly sunny, a touch of high cloud from afternoon. Northwesterlies pick up after midday.
Highs: 17-19

Wellington
Sunny spells and increasing cloud with breezy northwesterly winds.
High: 17

Marlborough & Nelson
Mostly sunny with some high cloud, more so from afternoon. North to northwesterly winds pick up after midday.
Highs: 16-19

Canterbury
Sunny areas and some high cloud, northwesterly winds.
Highs: 16-18

West Coast
Showers, perhaps some rain at times. Westerlies freshen from afternoon.
Highs: 12-14

Southland & Otago
Cloudy with showers about Southland, west to northwest winds becoming strong in the afternoon with a risk of gales. Otago has mostly cloudy skies, there may be a spit of rain at times otherwise mainly dry, winds lighter.
Highs: 12-15

By Weather Analyst Aaron Wilkinson – WeatherWatch.co.nz