Heavy rain will hit many parts of the South Island tomorrow before making its way up the country, hitting most areas in need of some water.
Phillip Duncan of WeatherWatch says a large low in the South Tasman Sea and Southern Ocean is today starting to connect with more subtropical air to the north of the country.
"The good news is that most areas that need rain will get some this week -- and some in the west and northwest may get plenty," he says.
"While it means some very warm, over-20-degree-nights ahead, it also means dry farms, gardens and water tanks will get a much-needed, mid-February top-up."
Heavy bands of rain are forecast to bubble up over the eastern Tasman Sea then move into the western and northwestern coastlines of both islands as the incoming southern low taps into the very tropical air just to New Zealand's north at the moment.
Tomorrow there will be heavy downpours on the South Island's west coast and northwest corner as well as the deep south.
Canterbury has an 80 per cent chance of rain mid-week and Southland and Otago are also likely to experience rainfall.
"Overnight Wednesday the downpour risk shifts into the North Island -- then across Thursday heavy tropical-fuelled rain could affect regions across both islands, in particular the northern half of the North Island and the western side of the South.," Mr Duncan says.
By Friday rain should stop on the east coast of both islands but could continue in the north and west.
MetService has already started issuing rain warnings -- for the rain forest in Fiordland and neighbouring Westland.
However, there is a high chance more rain warnings will be issued across other more populated parts of the country, mainly west and northwest, over the next day or two.
The government forecaster also says there is moderate chance of severe gales in the east, around the middle of the country.
Meanwhile Tropical Cyclone Winston could be heading back toward New Zealand in a week's time.
It is continuing to track northeast back towards the tropics. In a few days it is likely to stop this track and make a 180 degree U-turn which could take it back down towards New Zealand.
"It's like spinning a coin on a table and watching it weave and meander along" says Mr Duncan.
"It seems to have a mind of its own and is tracking around north of the very big blocking high to New Zealand's east. As this high moves away to the east it opens up the chances for Winston to again head back south -- for now it's in a holding pattern waiting to drop south when the high moves away."
Currently Tropical Cyclone Winston poses no direct threat to New Zealand but it remains closely monitored.
Main centres outlook
Today: Cloudy periods, showers. Northeasterlies. High 25C.
Tomorrow: Showers, turn to rain in evening. Northeasterlies strengthen. High 25C.
Today: Cloudy periods, odd light shower. Northeasterlies. High 26C.
Tomorrow: Showers, turn to rain in the evening. Northeasterlies, strengthen. High 25C.
Today: Fine spells, few showers. Northeasterlies. High 24C.
Tomorrow: Cloudy, odd shower. Northeasterlies. High 24C.
Today: Fine spells, chance of shower. NE breeze. High 26C.
Tomorrow: Showers, turning to rain in the evening. Northeasterlies. High 24C.
Today: Morning cloud then fine. Northerlies. High 24C.
Tomorrow: High cloud with rain from evening. Northerlies may turn to gale. High 22C.