Northland, Auckland, the Bay of Plenty and East Cape had a chance of some heavy falls on Sunday.
"As the low pulls away on Sunday afternoon, the weather improves for the upper North Island, but the lingering cloud could still bring some patchy drizzle."
A series of weak fronts would sweep over the west and south of the South Island, while another front would move up the South Island on Monday, bringing rain to the North.
Road safety charity Brake had a warning for rugby fans planning to watch the semifinals on Sunday and Monday mornings.
"Brake is reminding drivers to make sure they're fit to drive before setting off, and during the journey," the charity said. "That means having enough sleep before a journey, taking regular breaks during a trip, and not drink or drug-driving."
Drivers should take at least a 15- minute break from driving every two hours during long trips, and get a good night's sleep before setting off.
Superintendent Steve Greally, national manager road policing, said the risk of fatal or serious crashes was 14 per cent higher nationally over Labour weekend.
Police would issue "yellow cards" to dodgy drivers, Mr Greally said.
"The yellow card reminds people that if they incur 100 demerit points over a two-year period, they will have their licence suspended for three months," he said.
"We'll also be carrying out random alcohol checkpoints ... and will be breath-testing anyone stopped, anywhere, at any time."
A reduced 4km/h speed threshold would be enforced from Friday afternoon to Tuesday morning, police said.
Craig Foss, Associate Transport Minister, said he was worried about risks to people travelling on the roads this weekend.
"Sadly, this year's road toll is likely to be higher than last year's."
Northland District Health Board chief medical officer Dr Mike Roberts said a spate of crashes over the past fortnight had left people with serious injuries. "One of these crashes had involved two children who had not been restrained in car seats resulting in both ending up with broken femurs."
Dr Roberts said people should "slow down, wear seat belts, drive sober and take breaks".
Drivers needed to be patient, as there would be more traffic than normal on roads, he said.
Mountain Safety Council chief executive Mike Daisley said people heading into the wild, even experienced trampers, should plan their trips carefully.
"Although temperatures are rising, conditions are still wintry around much of New Zealand," Mr Daisley said.
The official Labour weekend holiday period begins at 4pm today and ends at 6am on Tuesday. Last year the weekend toll was three, from 78 reported injury crashes.
Weekend forecast
• Auckland: Rain with some heavy falls tomorrow, will clear by Sunday afternoon. Cloudy periods on Monday, chance of rain. Highs around 18C, lows around 12C.
• Hamilton: Rain with come heavy falls tomorrow clearing Sunday morning. Few showers around on Monday. Highs around 20C, lows around 8C.
• Tauranga: Rain developing midday tomorrow and easing on Sunday. Fine spells with chance of showers on Monday. Highs around 20C, lows around 11C.
• Wellington: Fine tomorrow and Sunday with chance of a shower. Cloudy periods on Monday, Highs around 17C, lows around 10C.
• Christchurch: Morning cloud tomorrow will clear for a fine day. Morning showers will ease on Sunday, and fine day on Monday. Highs around 16C, rising to 21C on Monday. Lows around 5C.
• Dunedin: Fine day tomorrow and morning showers clear on Sunday. Monday will be fine, chance of late rain. Highs around 15C, rising to 21C on Monday. Lows around 6C.
