Northwesterly winds are forecast to turn into severe gales gusting up to 120km/h in exposed areas.
A MetService spokesman warned locals to keep a close eye on weather alerts and updates.
"People are advised to keep up-to-date with the latest forecasts in case any updates are made.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."
The National Institute of Water and Atmospheric Research said its models showed the areas at the greatest risk of feeling gusts of up to 120km/h today were on the west coast particularly in the South Island.
"Possible impacts [as a result]: localised power outages, localised wind damage, tricky travelling," Niwa said.
People in those areas were also warned about localised structural damage caused by severe gusts over the next two days, at least, and downed trees.
SUNNY IN THE NORTH:
Despite bad weather conditions in the South Island, those in the North Island are enjoying a brighter day.
Auckland has a significant temperature high of 16C and overnight low of 10C. However, MetService was reporting Auckland's weather as feeling more like "two layers of clothing" this morning.
WeatherWatch analyst Aaron Wilkinson said it is a mostly sunny day for much of the North Island; save for a few cloudy areas for some western areas.
"Perhaps the risk of a brief shower or two, at times, about Taranaki through to Kapiti."
Wilkinson said those on the West Coast might also be in for a "rumble of thunders or two" later this evening.
High cloud with rain and showers would spread into Southland and Otago early tonight.
Just before 11am, the current extremes around the country had Christchurch the warmest place to be - with a temperature high of 18.3C. The coldest place was in Hokitika, with a temperature high of 10.3C.
The windiest spot was in Whanganui, where there were gusts of up to 35km/h.
Today's weather
WhangΔrei 18C high, 8C low. Morning cloud and chance of shower, then becoming fine.
Auckland 16C, 10C. Morning cloud and chance of shower, then becoming fine.
Hamilton 16C, 8C. Fine. Westerly winds.
Tauranga 17C, 10C. Fine. Westerly winds.
New Plymouth 15C, 12C. Partly cloudy, but cloud increasing at night with chance of shower.
Napier 20C, 12C. Fine with northwest breezes.
Whanganui 17C, 11C. Fine spells, but cloud increasing this evening. Northwesterly winds.
Wellington 15C, 11C. Fine then cloud increasing this afternoon. Strong northwesterly winds.
Nelson 15C, 10C. Increasing cloud. Chance of spot of rain from late afternoon.
Christchurch 20C, 8C. Increasing high cloud. Winds becoming gusty northwesterly by this evening.
