Police have warned driving conditions could be hazardous as storms could produce downpours with between 25mm and 35mm of rain falling in an hour.
Rainfall of this intensity could cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.
Police said motorists needed to exercise caution, maintain safe following distances and keep their speed suitable for the severe weather.
The weather was looking clearer over the weekend, Mr Coutts said.
"The low that is associated with these frontal systems is going to cross tomorrow night and there will be a southerly flow over the weekend and it will fine up over much of Northland and Auckland."
He said a few showers were possible for Sunday afternoon before a high would move in early next week.
WEEKEND WEATHER
Whangarei:
Friday - A chance of showers, with thunder easing in the evening. Northerlies dying.
Saturday - A few showers. Southerlies developing.
Sunday - Fine spells. Southwesterlies.
Auckland:
Friday - A chance of showers, with thunder easing in the evening. Northeast dies.
Saturday - Showers, clearing in the afternoon. Southerlies developing.
Sunday - Mainly fine with some evening cloud. Fresh southwest.
Tauranga:
Friday - Rain, some heavy falls, and a chance of thunder until evening.
Saturday - Showers, clearing later. Southerlies developing.
Sunday - Morning cloud, then fine with southwesterlies.
Hamilton:
Friday - Rain turns to showers in the afternoon, chance thunder.
Saturday - Showers, clearing later in the day. Southerlies developing.
Sunday - Mainly fine with some evening cloud. Southerlies easing.
Wellington:
Friday - Cloudy with light rain developing in the morning. Southerlies.
Saturday - Light rain clears, then fine spells. Southerlies easing.
Sunday - Fine, morning and evening cloud. Southerlies then northerlies.