New Zealand: Adverse weather forecast across western parts of South Island through at least Feb. 7 /update 5

Event

Heavy rainfall, strong winds, and possible thunderstorms are forecast across western parts of South Island through at least Feb. 7. The heaviest downpours are expected to occur from late Feb. 4 through early Feb. 6. Rainfall totals of up to 30 cm (12 inches) are possible over mountainous areas of the affected region and totals of around 8-14 cm (3-5.5 inches) are expected at lower elevations in some areas. Winds gusting up to 120 kph (75 mph) are possible in southeastern parts of South Island. Heavy downpours could trigger flooding in low-lying areas and landslides on unstable slopes and strong winds may cause property damage and power outages.

As of early Feb. 4, the New Zealand National Meteorological Service (MetService) has issued the following weather warnings across the affected area:

• Orange Heavy Rain Warnings (the middle level on a three-tier scale): Westland south of Otira and Fiordland north of Doubtful Sound.

• Orange Strong Wind Warning: Fiordland.

• Yellow Heavy Rain Watch: Tasman west of Motueka; Buller and Westland from Otira northwards; the headwaters of the Canterbury lakes and rivers; and the headwaters of the Otago lakes and rivers.

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 flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed or 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 delays and cancellations at regional airports. 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
NZ Transport Agency