New Zealand: Heavy rainfall and thunderstorms forecast in northern region through at least March 25 /update 2

Event

Heavy rainfall, thunderstorms, and strong winds are forecast over most of North Island through at least March 25. Forecast models indicate that a low-pressure system will bring heavy rain to much of North Island, with the rain starting to ease from the west the evening of March 23.

Authorities have declared a state of emergency across the entire Gisborne Region due to flooding. At least 150 people have been evacuated from Mangatuna, Uawa, Anaura Bay, Kaiaua, Tokomaru Bay, and Tolaga Bay, while 750 homes are without power in the Tolaga Bay and Tokomaru Bay areas.

As of March 23, the New Zealand National Meteorological Service (MetService) has issued the following warnings:

• Red Heavy Rain Warning (the highest level on a three-tier scale): Gisborne; a further 15-20 cm (6-8 inches) of rain is forecast. The heaviest rain has eased but is likely to resume the late afternoon of March 23. The heavy rain is likely to cause significant flooding and landslides; travel is likely to be disrupted. Thunderstorms with localized heavy rain are possible from late March 23 through early March 24.

• Orange Heavy Rain Warning: Bay Of Plenty, Hawke's Bay, and Taranaki; up to 18 cm (7 inches) of rainfall could occur in the area, especially in Hawke's Bay.

• Yellow Heavy Rain Watch: Taupo.

• Severe Thunderstorm Watch: Auckland, Bay of Plenty, Gisborne, Northland, and Waikato.

Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days.

Hazardous Conditions
Sustained heavy rainfall could trigger additional flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed or a lack of stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall. Power outages could occur throughout the affected area.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. Authorities are requesting residents to delay their journeys and avoid unnecessary travel. State Highway 35 is temporarily reopened until 18:00 March 23 between Gisbourne and Tolaga Bay as well as between Potaka and the Ruatoria Intersection to allow residents to return home or travel for essential purposes in advance of the additional heavy rain forecast from the evening of March 23. SH35 will remain closed between Tolaga Bay and Te Puia Springs due to unsafe conditions. The road in Tolaga Bay Gorge is only passable for four-wheel drives due to flooding and multiple landslides. Multiple other local roads in Gisbourne are closed due to flooding, landslides, and damage. More information about road closures in Gisbourne can be found here. The disruptive weather may cause flight disruptions at airports in the region, including Auckland International (AKL) and Gisborne (GIS) airports.

Authorities may temporarily suspend port operations if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding could block regional rail lines; freight cancellations are possible in areas with heavy rainfall and potential track blockages. Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. If there is severe damage to infrastructure, repair or reconstruction efforts may result in residual disruptions.

Advice

Monitor local media for weather updates and related advisories. Confirm all transport reservations and business appointments before travel. Make allowances for localized travel delays and potential supply chain disruptions where flooding has been forecast. Do not drive on flooded roads. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

New Zealand National Meteorological Service
Waka Kotahi NZTA Auckland & Northland Twitter
Waka Kotahi NZTA Central North Island Twitter
Gisborne District Council Facebook