A northerly airflow lies over New Zealand today with a couple of fronts bringing rain to western regions, expect downpours and thunderstorms also, perhaps even a small tornado, more so about the western North Island.

Northland, Auckland, Waikato & Bay Of Plenty
Thickening cloud, showers start spreading down from the north during the morning, heavy falls and thunderstorms from afternoon. Northerlies pick up later in the day then change strong westerly overnight.
Highs: 19-23

Western North Island (including Central North Island)
Partly cloudy, chance of a light shower for Taranaki and Kapiti. Cloud starts to thicken from afternoon then rain develops late afternoon or evening, a chance of heavy falls and thunderstorms then easing a touch overnight as northerlies change gusty westerly.
Highs: 19-24

Eastern North Island
Mostly sunny, rain spreads from the west late afternoon or evening. Northerly winds pick up later in the day.
Highs: 24-29

Wellington
Partly cloudy, rain moves in overnight. Strong north to northwesterly winds.
Highs: 19-22

Marlborough & Nelson
Mostly sunny, spits of rain develop about Nelson in the afternoon. Overnight rain for most. North to northwesterly winds.
Highs: 19-22

Canterbury
Sun and increasing high cloud, late afternoon spits of rain possible mainly about South Canterbury. North to northwesterly winds becoming a bit breezy in the afternoon. Overnight may see a few spits or showers for most, perhaps some rain for the Kaikoura area as winds change southwest.
Highs: 18-25

West Coast
Rain with heavy falls, rain may not become heavy about Buller till afternoon. Rain eases from evening as northerly quarter winds change southwest.
Highs: 14-18

Southland & Otago
Dry this morning for Southland and eastern Otago with high cloud, rain about the Lakes District with heavy falls close to the western ranges. A few showers develop elsewhere this afternoon, perhaps a few isolated heavy falls with some thunder, clearing evening. Northerlies tend northwest in the afternoon.
Highs: 16-21