A low passes over and away to the east of New Zealand today gradually letting in a cold southwesterly airflow.

Northland, Auckland, Waikato & Bay Of Plenty
Showers, some may be heavy in the afternoon with possible thunderstorms then easing in the evening. Northwesterly winds change southwest by evening.
Highs: 18-22

Western North Island (including Central North Island)
Mostly cloudy, rain about Taranaki with heavy falls and possible thunderstorms then easing to showers in the afternoon as northerlies change southwest. Elsewhere expect a fairly cloudy morning with the risk of a shower, showers set in more during the afternoon then clearing evening.
Highs: 16-19

Eastern North Island
Mostly sunny with some high cloud, spots of rain about the Wairarapa with north to northwesterly winds changing southerly there in the afternoon at which point rain sets in a bit more. Rain clears in the evening. Remaining mainly dry further north.
Highs: 18-22

Wellington
Some rain, northerlies change southerly late afternoon. Long dry spells developing in the evening.
High: 16

Marlborough & Nelson
Morning rain (possibly heavy) eases, an isolated shower or two may continue for the rest of the day. Some sun breaks through in the afternoon then overnight cloud thickens up with a slightly higher risk of showers. Light winds.
Highs: 14-17

Canterbury
Any early showers clear, some sun may break through in the afternoon then later in the evening southwesterlies freshen bringing rain. Some snow lowers to 500m overnight.
Highs: 10-13

West Coast
Any early rain clears Buller, mostly sunny otherwise with southwesterly winds. In the evening some cloud develops with the risk of a shower.
Highs: 14-16

Southland & Otago
Dry first thing with some sun then southwesterlies develop mid morning for Southland bringing some rain, rain moves into Otago in the afternoon. Rain clears in the evening. Some snow may lower to 400m by evening then clearing.
Highs: 10-13

By Weather Analyst Aaron Wilkinson – WeatherWatch.co.nz