"What that can mean is rivers and streams could rise rapidly, you could get slips and there is a knock-on affect downhill in those rivers and streams and for bridges," Murray said.
MetService would issue another watch this morning but Murray said as soon as the front passed tomorrow another was set to move in, making for a rainy weekend for many.
Wellington would experience much of the wet conditions and Christchurch would also succumb by Saturday.
"It's not going to be a sunshiny weekend."
Further north there would be rainfall up to Taranaki and into the Eastern Bay of Plenty.
Today's forecast
Auckland
Cloudy patches with blue sky. Westerly winds reaching 20km/h. 21C.
Hamilton
Chance of afternoon drizzle. Northwesterly wind. 22C.
Wellington
Rain and drizzle throughout the morning. Low cloud but little wind. 17C.
Christchurch
Morning and evening high cloud. Fine spells and northeasterlies, 25km/h. 16C.
Dunedin
Evening cloud developing. Northeasterlies, 25km/h. 15C.