Northbound traffic, meanwhile, is severely choked just before the Johnstones Hill tunnel to Pūhoi Rd and in a separate section between Redvale and the Dairy Flat Highway off-ramp.
Motorists running the Southern Motorway gauntlet are expected to have the toughest time as they face the heaviest jams.
State Highway 1 between Manukau and Bombay was expected to be busy from 10.30am to 6.30pm today, and heaviest from 2pm to 5pm, Waka Kotahi NZ Transport Agency said.
The motorway is likely to be busy again tomorrow from 8.30am to 4.30pm, with extra heavy jams from 9.30am-12.30pm.
Waka Kotahi also expects a regular flow of motorists heading in the opposite direction and using the Southern Motorway to head north into the city.
The agency is warning motorists to expect busy traffic north from Bombay to Manukau from about 11am to 6pm each long weekend day from Saturday through to Monday.
For those planning a getaway north of Auckland, traffic will be much lighter than that heading south, but it will still be busy this afternoon.
The agency expects SH1 between Pūhoi and Wellsford to be busy from 1pm-6pm today.
Returning holidaymakers can then expect busy traffic on Monday between noon and 3.30pm as they head back into the city.
Auckland’s temperatures are expected to tumble in the coming days.
While Saturday is expected to be mainly fine with a high of 17C, showers are tipped for Sunday and Monday as temperatures drop to 16C and then 14C.
That pattern is expected across the country as winter marks its arrival on the first King’s Birthday long weekend since the Queen died.
Forecaster WeatherWatch is warning that a cold southerly blast is now hitting the country and is likely to bring snow.
WeatherWatch’s Philip Duncan said the front was moving north from the Southern Ocean.
It would send Monday daytime temperatures as low as 11C in the North Island and lower in the South Island.
It was already bringing thunder and lightning to the west, with 37.8mm of rain hitting Greymouth in one hour last night and 21.6mm falling in one hour on New Plymouth this morning, MetService said.
WeatherWatch’s Duncan said South Islanders could expect snow on the mountains, including those close to Queenstown.
However, he did not believe it would amount to a major snow event.
Along with the cold temperatures, windy and unstable weather would hit the top of the North Island and parts of the South Island.
In Hamilton, meanwhile, the weather front will see temperatures drop from 17C today to 12C by Monday.
Possibly heavy rain is expected this afternoon, while Waka Kotahi said there could be very heavy traffic on Monday going north on SH25 at Tairua and SH1 from Tīrau to Karāpiro as holidaymakers headed back to Auckland.
Tauranga can expect the odd shower today for a top of 18C before temperatures drop to 14C on Monday.
Napier can expect a pleasant high of 22C today with clouds before the cold front also makes its presence felt, pushing temperatures down to 15C by Monday.
MetService is not forecasting much rain for the region.
New Plymouth will go from a high of 18C today to 13C by Monday, with showers and rain on Sunday and Monday.
Wellington can expect a fine start to the long weekend with sunshine and tops of 17C today and 14C tomorrow.
Showers and rain will then catch up with the capital as temperatures fall to 14C on Sunday and 12C on Monday.
Wellington traffic is expected to be heaviest on SH2 between Remutaka Hill, the city and Featherston.
Waka Kotahi expects northbound traffic to be busy today from noon to 6pm and heaviest from 3pm-5pm.
Returning traffic in the same stretch of road is likely to be busy on Monday from 11.30am to 5.30pm.
Christchurch can expect bright, fine days today and tomorrow with tops of 16C and 13C, according to MetService.
Cloud and rain should then hit for highs of 14C and 12C on Sunday and Monday.
Temperatures would drop even lower to 11C later in the week as proper wintry weather hit the city, WeatherWatch’s Duncan said.
Dunedin is set for a mostly fine high of 15C today before rain and cold weather hits on Sunday for a high of 11C and overnight low of 6C.
Queenstown can expect overnight lows to drop to 1C as heavy rain arrives by Sunday.
