Heavy rain is set to fall over most of New Zealand today as a low creeps in from the Tasman.
The front is expected to move east from the Tasman Sea towards the South Island over today, and settle in for the next couple of days, MetService said.
Forecaster Geoff Sanders said an associated front would also move in over the central and north of the North Island, preceded by a moist northerly flow.
A heavy rain warning was in place for the Nelson Ranges which was expected to bear the worst weather, with torrential rain throughout the morning, however this would ease by the evening. The heaviest falls were expected during the late morning and early afternoon.
Heavy rain and thunderstorms were also expected in the far north, with the slight possibility of small tornados.
Thunderstorms coming in with the front off the Tasman were expected to affect the far north of Northland just before midday. MetService said the storms could produce up to 25mm rain in an hour and strong winds gusts of up to 110kmh, but they would see a high of up to 17 degrees.
New Plymouth could also expect some thunderstorms.
A heavy rain watch was in place for the ranges of Buller and Westland from midnight last night through to early tomorrow morning, and also about eastern Bay of Plenty from this evening to early Tuesday morning.
Sanders said western places such as Taranaki may see the sun for parts of today, however the low coming in from the east would "whip up most of the cloud around it" and this would cover most places.
Despite this, temperatures across much of New Zealand have risen slightly with the main centres - Auckland, Wellington and Christchurch - expecting highs of between 12-15 degrees.
Sanders said the periods of heavy rain would set in throughout much of New Zealand right up until Wednesday.
"But it's not until later Thursday we get a narrow ridge coming in over the country."
He said that would dry the country out again as it brought with it strong northerly winds.
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