However the front will clear by late Saturday and rainfall will ease, she said.
Auckland should see morning showers increase to heavy rain in the afternoon tomorrow.
It will ease by Saturday afternoon, Ms Moes said.
There will be bursts of rain and isolated downpours over the South Island's West Coast tomorrow morning.
"A moist northerly flow is expected to spread over the country tonight and tomorrow, with rain expected for many places, especially in the north and west of both islands."
Franz Josef is forecast to get very heavy downpours, WeatherWatch said, and isolated flooding is possible on the West Coast. The risk for flooding is highest tomorrow and into the early hours of Saturday for the West Coast, late tomorrow and Saturday morning for Nelson and overnight tomorrow and Saturday for the north of the North Island.
Whangarei
Tomorrow: Periods of rain, possibly heavy. Northerlies. 23C.
Saturday: Rain, briefly heavy, easing to showers. Westerly change. 26C.
Auckland
Tomorrow: The odd shower, then rain towards evening. Strong northeasterly. 23C.
Saturday: Rain, briefly heavy, easing to showers. Westerly change. 25C.
Hamilton
Tomorrow: Cloud increasing, rain develops from afternoon. Northeast. 23C.
Saturday: Rain, briefly heavy, easing to showers. Northerly dying. 24C.
Tauranga
Tomorrow: Mostly cloudy. A few showers, then evening rain. Northeast. 22C.
Saturday: Rain, possibly heavy, easing to showers. Northerlies. 24C.
Wellington
Tomorrow: Cloud increasing, rain develops evening. Northerlies. 20C.
Saturday: Rain easing to showers. Northerlies. 21C.
Christchurch
Tomorrow: High cloud, evening rain. Northeasterlies. 18C.
Saturday: High cloud, a few spots of rain possible. Northeasterlies. 20C.
Dunedin
Tomorrow: High cloud, rain at times from morning. Northeast. 17C.
Saturday: High cloud, a few spots of rain possible. Northeasterlies. 19C.