Wellington is forecast to reach 7C, and Dunedin 6C.
While most of the country's main centres will be shaking off the icicles tomorrow morning, the sun should be out in many places, MetService meteorologist Sarah Haddon said.
The sun would be short-lived though, even colder weather is expected to roll in later this week, she said.
Overnight the clouds are expected to clear, which is what brings the temperature down, she said.
"Cloud cover inhibits some of the cooling, the clear skies overnight is the thing that really brings the temperature down."
Despite the clear skies, there will be some "quite strong north westerly winds" bowling through many places.
"That will be something to watch out for."
Weather chaos today forced a Cook Strait ferry to take a seven hour journey to avoid rough seas.
The Bluebridge ferry tried to dodge the worst of the wild weather which last night saw 4-metre swells and southerly winds tipping just under 100km/h whip through the passage.
Strait Shipping spokesman Ed Menzies said in order to make the trip more comfortable for passengers the ship's master took a more southbound course and slowed the vessel which avoided the worst of the swell but meant the journey took seven hours.
The crossing normally takes around three hours.
MetService today issued a fresh weather watch for northwest gales developing over the South Island tomorrow with the possibility of destructive gales in Fiordland, Southland, Otago and parts of Canterbury.
This morning Wellington roads were affected by flooding and a passenger train struck a tree that had fallen on the tracks after wild weather left a trail of havoc across the lower North Island.
The Wellington to Johnsonville line was delayed after an early morning commuter train hit a tree.
All train services on the Melling line were cancelled after strong winds damaged barriers between Petone and Wellington.
