A storm lashing southeast Australia with rain and snow will make its presence felt in New Zealand from tomorrow.
The deepening low, currently over the Tasman Sea, will move on to the lower South Island from early tomorrow, MetService meteorologist Andrew James says.
Rain will spread over western parts of the South Island first, while the storm's associated front will bring rain to the west of the North Island, reaching Auckland in the afternoon/evening.
Over Saturday the rain will spread over the whole country.
"We are in for a wet weekend," James said.
MetService has issued heavy rain warnings for parts of Westland from 8am to 11pm tomorrow with up to 100mm forecast in the ranges.
Heavy rain is also expected about northwest Nelson and northern Fiordland, and Taranaki and Tongariro National Park in the North Island.
On Saturday and Sunday another low over the western Tasman Sea is expected to maintain the moist north to northeast flow over New Zealand.
WeatherWatch analyst Philip Duncan said the North Island could be in for some very heavy rain.
"The main threat for New Zealand is this weekend in the upper half of the North Island as very heavy bands of rain slowly track eastwards."
Converging sub-tropical winds - northwesterlies from the Tasman low and northeasterlies from the departing high - would create a very heavy, potentially torrential, narrow slow moving band of rain, he said.
"[It] will cross over the northern half of the North Island from Saturday afternoon to Monday morning at this stage."
MetService said there was potential for further heavy rain from Fiordland to northwest Nelson.
Rain could be heavy about western areas in the North Island on Saturday and Sunday, and Bay of Plenty and the Gisborne ranges on Sunday and Monday.
Temperatures are forecast to stay fairly mild in the North Island, with Auckland forecast to hover around 20C through to mid next week.
The South Island, however, is in for a cool southerly change on Saturday, with Christchurch dropping to a maximum of 14C, and just 12C on Sunday.
Temperatures are forecast to remain in the low teens across the South Island through next week.
Today, a ridge of high pressure is keeping the weather relatively settled throughout the country.
This morning's fog in Auckland is forecast to clear late morning for a fine day, with a high of 19C.
Similar conditions are forecast across the North Island today and tomorrow until late afternoon.
In the South Island there might be some isolated showers in the afternoon, before the low arrives from the Tasman.
