New Zealand: Adverse weather forecast over parts of western and central New Zealand through at least June 10 /update 2

Event

A weather front is forecast to bring heavy rainfall and thunderstorms across most of South Island and southern North Island through at least June 10. Thunderstorms may be accompanied by strong wind gusts, hail, and possible small tornadoes. Snowfall is also possible over areas of higher elevation in western South Island, and rough seas are forecast for parts of southern North Island.

As of June 9, the New Zealand National Meteorological Service (MetService) has issued the following weather warnings across the affected region:

• Orange (middle level on a three-tier scale) Heavy Rain Warning: Horowhenua about and south of Levin, Wellington north of the Ngauranga Gorge, the Tararua Range, Buller, and Westland north of Okarito. Further rainfall of 3-5 cm (1-2 inches) are possible in the warning areas.

• Orange Strong Wind Warning: Wellington, Wairarapa about and south of Featherston, and the Marlborough Sounds.

• Yellow Heavy Rain Watch: Tasman west of Motueka, the Richmond and Bryant ranges, the Rai Valley, northern Marlborough Sounds, Westland, and Buller.

• Yellow Severe Thunderstorm Watch: Nelson, Buller, and Westland

• Yellow Heavy Snow Watch: central Otago, the Queenstown Lakes District, and the Canterbury High Country west of Otematata and about and south of Mount Cook village.

• Yellow Strong Wind Watch: Wairarapa north of Featherston, the Tararua District, the ranges of Hawke's Bay about and south of Te Haroto, and Taihape.

• Road Snowfall Warning: Arthur's Pass (SH73), Porters Pass (SH73), Haast Pass (SH6), Lindis Pass (SH8), Milford Road (SH94), and Crown Range Road.

• Heavy Swell Warning: Kapiti-Porirua Coast from Otaki to Cape Terawhiti.

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

Authorities reported major power outages in Wellington City early June 9; services have since been restored.

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 affected regions. Flooding could block regional rail lines; freight cancellations are possible in areas that see 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. Review contingency plans and be prepared to move quickly to shelter if tornado warnings are issued. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

New Zealand National Meteorological Service