New Zealand: Heavy rainfall forecast in parts of western South Island and western North Island through at least early April 22 /update 2

Event

Heavy rainfall is forecast in parts of western South Island and western North Island through at least early April 22. A front is forecast to track across the South Island the evening of April 21 through early April 22 before moving over the North Island through the afternoon of April 22. As of April 21, the New Zealand National Meteorological Service (MetService) has issued the following warnings:

• Orange Heavy Rain Warning (second-highest level on a three-tier scale): Buller, Fiordland north of Breaksea Sound, northwestern Marlborough Sounds, Rai Valley area, Richmond and Bryant ranges, Tasman west of Motueka, and Westland; additional rainfall of up to 14 cm (5.5 inches) is forecast especially in the ranges of Westland. Thunderstorms are also possible.

• Yellow Heavy Rain Watch: Auckland, Coromandel Peninsula, Mount Taranaki, Northland south of Whangarei, Waikato north of Hamilton, and the headwaters of Canterbury and Otago lakes and rivers.

Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days. The heavy rain is likely to lead to rapid water level rises in rivers and streams. Surface flooding, landslides, and hazardous driving conditions are possible.

A lightning strike at the Frankton grid exit point resulted in power outages for more than 12,000 people in Queenstown, Glenorchy, Frankton, and Arrowtown early April 21; authorities have since restored power. The Queenstown International Airport (ZQN) is operational. The Glenorchy-Queenstown Rd is closed at Boundary Creek due to a landslide. Much of SH 6 from Hokitika to Haast and Inangahua to Punakaiki, and SH 67 from Fairdown to Waimangaroa, are flooded; officials have advised motorists to proceed with caution.

Hazardous Conditions
Sustained heavy rainfall could trigger 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. The disruptive weather may cause some delays and cancellations at airports in the region, including but not limited to Queenstown International Airport (ZQN) and Auckland International Airport (AKL). 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