The traffic will be especially heavy, with crawling bumper-to-bumper conditions expected 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.
Busy traffic north from Bombay to Manukau is expected from about 11am to 6pm each long weekend day from Saturday through to Monday.
For those planning a getaway north of Auckland, traffic should be lighter.
Waka Kotahi expects SH1 between Puhoi and Wellsford to be busy from 11am-2pm today.
Returning holidaymakers can then expect busy traffic on Monday between noon and 3.30pm as they head south back into the city.
For those sticking around in Auckland, forecasters said today is the day to get out and about.
Aucklanders can expect a mainly fine 17C, interrupted by only isolated showers, forecaster MetService said.
Showers and some heavy falls of rain are then tipped for Sunday afternoon with a maximum of 16C, before Monday drops to a chilly 13C.
That pattern of falling temperatures by Monday is expected across the country.
Monday daytime temperatures will fall as low as 11C in the North Island and even lower in the South Island, MetService said.
The cold snap marks winter’s arrival and comes Wellington was among parts of the country to record unseasonably warm temperatures yesterday.
MetService said its Wellington Airport gauge recorded a high of 18.5C yesterday, 0.1C higher than the previous hottest June day set in 2002.
Hastings and Napier were also the country’s warmest places, hitting 23C yesterday - or 7C above average for June.
Forecaster WeatherWatch said yesterday and today are the “calm before the storm”.
They warn a cold southerly blast is already hitting New Zealand, moving north from the Southern Ocean and bringing snow.
The snow is expected on the South Island’s mountains, including those close to Queenstown.
However, WeatherWatch did not believe it would amount to a major snow event.
Heavy rain watches are now in place for the lower West Coast as well as a road snowfall warning for the SH94 Milford Rd.
Along with the cold temperatures, windy and unstable weather will also hit the top of the North Island and parts of the South Island.
In Hamilton, meanwhile, the weather front will lead temperatures to drop from a mainly fine 15C today, to a wet 15C on Sunday and then chilly 12C on Monday.
Waka Kotahi also warns there could be very heavy traffic on Monday going north on SH25 at Tairua and SH1 from Tīrau to Karāpiro as holidaymakers head back to Auckland.
Tauranga can expect fine weather today for a top of 17C before temperatures drop to 14C on Monday.
Napier can expect a fine 17C today before the cold front also makes its presence felt, pushing temperatures down to 15C by Monday with scattered rain.
New Plymouth can expect fine 16C today before a wet Sunday leads into a chilly 13C on Monday.
After yesterday’s record day, Wellington is set for a fine but cold 14C today.
The long weekend will then turn rainy with highs of 15C and 13C on Sunday and Monday.
Wellington traffic is expected to be busy northbound on SH2 between Remutaka Hill, the city and Featherston from 10.30am-12.30pm.
Returning traffic in the same stretch of road is likely to be busy on Monday from 11.30am to 5.30pm.
Christchurch can expect a bright, fine day today heading for a top of 13C after coming off an overnight low of 2C, according to MetService.
Heavy rain then hits along with tops of 14C and 11C 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 14C today before some showers and clouds take over on Sunday and Monday for highs of 11C.
Queenstown can expect overnight lows to drop to 0C tonight.
