Weather warning: 'Significant' sub-tropic storm set to drench upper North Island

A satellite image showing the major weather system that will hit Auckland, Northland and impact most of the North Island on Tuesday. Photo / Niwa

A sub-tropical deluge is set to soak the flood-ravaged top of the country tonight, as the region braces for more than a day of non-stop heavy rain and gales.

While forecasters are confident today's rainstorm won't be on the same scale as last month's destructive one-in-500-year event, those living in the top of the country have now being told their region is now under a heavy rain warning and strong wind watch.

Drought-stricken Auckland, Great Barrier Island and Coromandel are also in line for gales and rain, with a heavy rain and wind watch issued for Tuesday.

"This heavy rain may bring a significant impact, especially to Northland where the ground is already saturated with water from a previous heavy rain event," warned MetService.

It also said the recently water-logged region was likely to experience surface flooding and rapidly rising rivers and streams.

It's the second severe storm in a matter of weeks for flood-ravaged Northland. Just three weeks ago the far north was hit by a deluge that swamped farm land, forced residents from their homes and brought down hillsides across roads, with State Highway One near Mangamuka still cut off by a massive slip.

Forecasters say the system predicted to soak the region overnight - potentially bringing up to 120mm of rainfall - will prove more of a short, sharp hit than a slow-moving event.

⛈️ Heavy rain and strong winds 🌬will affect Northland during the first half of Tuesday before spreading further south.

While the fast moving nature of the low means that high rainfall amounts won't be widespread, there will still be a risk for localised flooding. pic.twitter.com/8A2YQgj7Ji

— NIWA Weather (@NiwaWeather) August 9, 2020

In warnings released this morning the MetService says Northland is expected to get between 70mm to 120mm of rain from 11pm until 5 pm Tuesday.

Flooding and slips were likely and driving across the region could be hazardous.

At the same time the region would be battered by winds with northeasterly winds getting up to gale force at times.

A heavy rain and strong wind watch is also in force for Auckland and Coromandel Peninsula tomorrow. Up to 75mm of rain is expected to fall between 6am and 9pm tomorrow.

MetService meteorologist Stephen Glassey said while there was a risk of heavy rain for areas, the area of low pressure wouldn't bring conditions to compare with the disastrous storm that hit the region in mid-July.

"It's not going to be a long-lived event as this system is moving through relatively fast."

Glassey said a low-pressure system was expected to drag down moisture-packed air from the sub-tropics, booting its rain-making power as it swept down on to the upper North Island.

Exposed parts of Northland could receive between 70mm and 100mm over a period of hours on Tuesday morning.

Auckland commuters may be in for a wet drive to work tomorrow, with Niwa forecaster Chris Brandolino predicting the deluge to hit around rush hour.

"We're also looking at a pretty good chance of thunderstorms across Northland on Tuesday as well," he said.

The stormy weather is expected to skirt the eastern side of the upper North Island, bringing rain to eastern Waikato, Bay of Plenty and Gisborne and Hawke's Bay.

At this stage warnings and watches are confined to northern regions.