Weather: ‘Prepare for the worst, hope for the best’ as atmospheric river bears down

Nelson-Tasman residents are being told to prepare for hundreds of millimetres of rainfall hitting parts of the region from tonight, as an atmospheric river fuels intense downpours on northern and western regions.

Nelson Mayor Nick Smith said rainfall forecasts of up to 350mm in some places - and dropping within only two days - were “sufficiently serious to be concerned”.

“We should prepare for the worst and hope for the best.”

Northland will be slammed by 24 hours of heavy rain, which MetService is warning could last even longer. The warning is currently at orange, but could be updated to red later in the day - the highest level that the alerts reach.

People in the region should expect 80 to 130mm of rain on top of what has already fallen. Peak rates will sit around 10 to 20mm/h but could reach up to 35mm/h in localised areas.

Heavy Rain Warning (Orange) issued for Kapiti-Horowhenua, Marlborough, Nelson, Northland, Taihape, Taranaki, Taupo, Wairarapa, Waitomo, Wellington https://t.co/jZdvdpmLvs

— MetService Severe Weather Info (@MetServiceWARN) May 3, 2023

The tropically-charged storm is causing disruptions for commuters in Auckland and may cause slips and flooding across the country.

Fire and Emergency NZ (Fenz) said they are “closely monitoring” the unfolding event and are on standby to send resources where required.

The worst of the weather, however, is expected to skip Central Auckland as the atmospheric river moves along the western side of the country. But ferry services across the Gulf Harbour are cancelled on Thursday as a precaution.

However, Western parts of Auckland may not escape unscathed, with MetService forecasting periods of heavy rain and issuing a heavy rain watch for the area.

UPDATE - For Thu 4 May, all Gulf Harbour Ferry services have been cancelled due to weather forecasts. Except for the 06:30 Gulf Harbour to Auckland sailing (cancelled, no alter transport), all other services will be operated by alternative transport. ^CL https://t.co/e6A8DZuA6e pic.twitter.com/FHGNfUN35f

— Auckland Transport Travel Alerts (@AT_TravelAlerts) May 3, 2023

MetService is expecting the Northland, Bay of Plenty, Tasman, and Fiordland regions to be the worst affected by the downpours, and warnings and watches have been made.

Fire and Emergency deputy national commander Brendan Nally said crews are on standby to help those if needed during this extreme weather and are closely monitoring the forecast.

“Northland is already seeing some impacts of heavy rain, so we have sent resources, including some of our [urban search and resuce] capability to Kaikohe in Northland,” Nally said.

Taranaki, north of Opunake to Whangamomona, is also under the heavy rain warning, with a massive 350 to 450mm of rain about Mt Taranaki. Some 150 to 200mm of rain is expected west of Urenui to Stratford, and 100 to 150mm further east, with peak rates of 25 to 35mm/h.

The rain ramps up in Taranaki tomorrow morning under an Orange Warning, but there is the potential to be upgraded to Red🟠🔴

Possible impacts include flooding, slips, and rapidly rising rivers

Be sure to keep up with the latest updates on https://t.co/qHyE5zzql5 pic.twitter.com/rz6yfPGfnm

— MetService (@MetService) May 3, 2023

MetService advises residents in these areas that this is a “significant amount of rain” and the warning may be upgraded to red this morning. The warnings span until Friday morning.

The Nelson, Marlborough, Tasman, Tongariro National Park and Waitomo regions are also in the firing line. Residents should expect 200 to 300mm of rain in some places and 100 to 150mm elsewhere with peak rates of 15 to 25mm/h.

In the Nelson-Tasman region, forecasters were currently estimating over 250mm to 350mm of cumulative rainfall in some catchments over a 42-to-45-hour period beginning from tonight.

“Make sure you have a plan and check on your neighbours or loved ones to be ready for whatever happens,” Smith said.

“If the weather hits during the day, think about how you will get home or pick up your children from school. We want everyone to be safe if this bad weather does hit.”

Tasman mayor Tim King said local emergency managers were monitoring the situation and were on stand-by if required.

“Our rural support networks are already contacting farmers to make sure stock are safely out of flood zones,” King said.

“For any tourists to our region, we strongly recommend they stay away from rivers, as they could rise rapidly depending on the intensity of the rain.”

The mayors also recommended people avoid travelling during heavy rainfall and to keep the roads clear.

More rain warnings extend down the western coasts of both islands, with a warning for Wellington to Horowhenua, Westland south of Otira, and Fiordland north of Doubtful Sound.

Some areas of these regions will see thunderstorms that may bring rain at 35mm/h at their peak.

Fire and Emergency NZ Deputy National Commander Brendan Nally. Photo / Fenz

Nally said further Fenz deployments may occur as the event unfolds and authorities receive more clarity on the conditions on the ground.

“Although there is still some uncertainty about exactly where the rain will hit, we are ready to respond where we are needed. We have extra resourcing ready to be deployed at short notice,” Nally said.

“Our focus is on supporting our communities, some of which have already been affected by previous events this year, most notably Cyclone Gabrielle.”

MetService meteorologist Dan Corrigan warned residents who are likely be impacted to pay close attention to forecasts as their severe weather warnings could change as the storm evolves.

An atmospheric river as seen from above 🛰️.

This is the fuel for heavy rain that will impact parts of the motu. pic.twitter.com/ShxEopL2Oy

— NIWA Weather (@NiwaWeather) May 2, 2023

“MetService is keeping a close eye on this rain band, but there is still some uncertainty surrounding the details of when and where the heaviest rain will fall later this week,” Corrigan said.

The storm has boomeranged back on the country after dumping heavy rain in Northland and Coromandel earlier this week.

Yesterday, persistent rain caused flooding and rising river levels and triggered slips and cut off townships in the Bay of Plenty.

The Whakatāne River reached a second warning level according to the Bay of Plenty Regional Council as 230mm of rain fell in the catchment.

“We are advising farmers with stock on low-lying areas adjacent to the Whakatāne and Tauranga Rivers to immediately move stock to higher ground,” a spokesperson from the council said.

Photos emerged yesterday aftermath of a large slip in Whakatāne that cut power to a number of households. The slip took out powerlines and affected 674 customers.

Slip in Valley Rd, Whakatāne.

The townships of Tāneatua and Rūātoki were also cut off due to slips.

The low-pressure system has rolled over the country from the Tasman Sea, picking up and bringing lots of warm air and water.

Corrigan said a stubborn high-pressure system off New Zealand’s east coast was stopping the storm from following its normal path away from the country.

The humid, unsettled northerly flow was expected to affect the country until at least early next week, with multiple fronts embedded in the system likely to bring more rain.