Conditions should improve in the early evening, Mr Duncan said.
"School and rush hour motorists are advised to be aware of pockets of torrential rain which may make driving very difficult with limited visibility and surface water."
Hazards to watch for include limited visibility for motorists, surface flooding in localised areas, isolated thunderstorms, and a risk of slips north of the city.
MetService had a severe weather watch for Bay of Plenty and Rotorua, where localised heavy rain was possible tomorrow morning.
Meteorologist Philippa Murdoch said storms and showers were also expected to move down the North Island today.
Showers were expected for much of the country of the weekend before a welcome high next week.
Weekend weather:
Whangarei:
Today - A chance of showers, with thunder easing in the evening. Northerlies dying.
Tomorrow - A few showers. Southerlies developing.
Sunday - Fine spells. Southwesterlies.
Auckland:
Today - A chance of showers, with thunder easing in the evening. Northeast dies.
Tomorrow - Showers, clearing in the afternoon. Southerlies developing.
Sunday - Mainly fine with some evening cloud. Fresh southwest.
Tauranga:
Today - Rain, some heavy falls, and a chance of thunder until evening.
Tomorrow - Showers, clearing later. Southerlies developing.
Sunday - Morning cloud, then fine with southwesterlies.
Hamilton:
Today - Rain turns to showers in the afternoon, chance thunder.
Tomorrow - Showers, clearing later in the day. Southerlies developing.
Sunday - Mainly fine with some evening cloud. Southerlies easing.
Wellington:
Today - Cloudy with light rain developing in the morning. Southerlies.
Tomorrow - Light rain clears, then fine spells. Southerlies easing.
Sunday - Fine, morning and evening cloud. Southerlies then northerlies.
Christchurch:
Today - Mostly cloudy, occasional drizzle. Light winds.
Tomorrow - Morning and evening cloud, otherwise mainly fine. Light winds.
Sunday - Mainly fine with northeasterlies. Showers with a strong cold southwest change overnight.
Dunedin:
Today - Cloudy periods, with isolated showers this morning. Southerlies developing this morning, then dying out this afternoon.
Tomorrow - Cloudy periods. Light winds.
Sunday - Fine with northwesterlies at first. Late showers with a strong cold southwest change. Snow flurries possible about the hills overnight.
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