The temperature in Queenstown would plummet from a high of 28C today, to a high of 19C tomorrow.
The change would be a little less severe up north, with temperatures expected to stick around 25C or 26C.
There was a moderate risk of thunderstorms later on Thursday afternoon around Westland, Buller and Nelson up to Northern Marlborough.
Eastern parts of Taupo and the Bay of Plenty could be hit with stormy weather on Thursday afternoon.
Nelson Tasman Civil Defence Group Controller Roger Ball said the region was in for a wet, blustery Thursday.
"We expect 3 to 5m waves around the Nelson City area, plus king tides around midday Thursday and midnight Thursday," he said.
"With the low pressure from this system and the wind piling the sea into the head of Tasman Bay, sea level could be elevated up to a metre above predicted tide levels in Tasman Bay."
Ball was urging locals to take care in low lying areas like Rocks Rd, Rabbit Island and Takaka. Campers should move away from river mouths, he said, while motorists should revise their routes.
The Transport Agency had likewise issued a warning for drivers crossing the South Island's alpine passes.
The storm about to hit the West Coast could bring heavy rain, strong winds and high tides, which could result in road closures.
Journey manager Lee Wright said teams of contractors would be working to keep the main highways open, but drivers needed to play their part too.
The north was expected to escape the worst of the deluge, but would be hit by localised downpours and wind.
Coastal communities were also preparing for king tides and localised downpours on Thursday. When coinciding with stormy conditions, extreme high tides could cause flooding chaos.
The forewarning for flooding comes just weeks after coastal spots like Kaiaua were devastated by flooding.
Many residents in the coastline village were left with the daunting task of rebuilding their lives after huge waves burst over the sea bank and inundated houses this month.
The Hauraki District Council was urging residents to be prepared for more flooding that could come from a high tide at 8.45pm on Thursday and again at 9.20am on Friday.
Hauraki District Controller Steve Fabish, from the district council, said this storm was not anticipated to be as big as the one that kicked off the new year but residents should prepare for the worst.
"Have you thought about where you might self-evacuate to, such as friends and family, in the event you have to leave your home?" he said.