Auckland was left mopping up after being drenched by 55mm of rain in 14 hours, sparking flooding, downing trees and forcing the cancellation of today's Big Gay Out.

And on Monday morning, after the deluge, came a blanket of sticky heat - the city and parts of the North Island were sitting at 99% humidity shortly before 6am.

The sodden conditions saw dozens of weather-related emergency callouts across the region.

And while conditions have started to ease, weather modelling shows a tropical cyclone hammering parts of the Pacific could be set to hit New Zealand in the coming week.

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Auckland was coming out of the worst of the rain at 8pm tonight as the band of moisture began pushing away from the city's eastern suburbs.

"It is progressing southwest, there will be a brief clearance of the rain," MetService meteorologist Tui McInnes said.

There was a "risk" of the front moving northwest overnight which could spell further wet weather tomorrow evening.

Like the weather system of Cyclone Fehi two weeks ago, the rain was localised and could be heavy in some areas and light in others.

"The rainfall which was heavier can be isolated and localised.

"It might be heavy somewhere and someone a few kilometres across might not see much."

Unlike two weeks ago, the Waitakere Ranges did not protect the North Shore or the CBD today, which also got between 45mm and 55mm.

Fire and Emergency attended 25 weather-related callouts in Auckland between 6am and 8.30pm today.

Most of the call outs were related to flooding, while a couple involved felled trees, a spokesman said.

Marlborough, which had been pelted by 198.5mm of rain in the past 24 hours in its Western Ranges, was also beginning to come through the worst of it.

In Nelson, the Nelson Tasman Emergency Management Group reported rivers had risen rapidly in the district causing localised surface flooding and slips.

"Areas of most impact and concern have been Riwaka [Tasman District near Motueka] and Maitai River [the main river in Nelson City]."

In Stoke, a suburb of Nelson, firefighters had to pump water from the New World supermarket.

MetService had a severe weather warning in place for the area until midnight Sunday.

In the immediate future the active front looming over the North Island that had saturated much of the country was forecast to weaken from late Tuesday.

"On Wednesday, a ridge is forecast to spread over the South Island from the Tasman Sea while the front over the North Island continues to weaken.

"The ridge is expected to move north over the North Island on Thursday as northwesterlies strengthen across the South Island ahead of a front approaching from the Tasman Sea," MetService said.

The front would further weaken on Friday as it moved slowly over the South Island.

A motorist told the Herald visibility on Auckland's Southern Motorway was atrocious about noon today, with traffic crawling at about 50km/h.

Inner-city roads were "awash" with water, he said.

"It's absolutely bucketing down out there. Stay off the roads if you can. It's just horrendous."

The torrential downpour forced the cancellation of today's Big Gay Out at Pt Chevalier's Coyle Park due to health and safety risks associated with electricity connections.

Several beaches in Auckland were also placed on health-risk warning alerts after the heavy rain.

The warnings were in place for Mission Bay Beach, Browns Bay, Castor Bay, Herne Bay, Mairangi Bay, Narrow Neck, Okahu Bay, Point England and St Mary's Bay.

More than 50 beaches were affected in total, from Wenderholm Beach in the north down to Kawakawa Bay.

All of the warnings had been issued between noon and 1.30pm.

Niwa said there had been reports of surface flooding in Whangaparaoa, north of Auckland, and rapidly rising streams.