New Zealand: Severe weather forecast across parts of South Island through at least Sept. 13

Severe weather is forecast to continue across parts of South Island through at least Sept. 13. A front will track slowly northward over the lower South Island Sept. 12-13, preceded by moist northwesterlies and followed by a much colder southeast flow, bringing heavy rain and significant snowfall. Snowfall will likely lead to hazardous travel conditions in mountainous areas due to slippery roads and reduced visibility caused by blowing snow.

As of Sept. 11, the New Zealand National Meteorological Service (MetService) has issued the following weather warnings across the affected area:

• Orange Heavy Rain Warning (the middle level on a three-tier scale):  Fiordland from Doubtful Sound northward and Westland District south of Haast.

• Yellow Heavy Snow Watch: Canterbury High Country south of the Rangitata River, central Otago, and Queenstown Lakes District.

• Yellow Heavy Rain Watch:  Southland north of Lumsden.

• Road Snowfall Warning: Lindis Pass (SH8), Milford Road (SH94), and Crown Range Road.

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

Where precipitation falls as rain, flash and areal flooding are possible. This may occur in low-lying communities near watercourses and other large bodies of water and in urban areas with easily overwhelmed stormwater drainage systems. Sites downstream of large reservoirs may be subject to flash flooding after relatively short periods of intense rainfall.

Precipitation could fall as snow in the higher elevations over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in mountainous areas. Rain-induced landslides are possible in areas of elevated terrain; avalanches are also possible in mountainous areas where the snowpack has become unstable due to heavy snowfall. Power outages are likely throughout the affected area.

Floodwaters and related debris will probably render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas will likely cause significant traffic congestion. Heavy snow will make driving hazardous in some areas; authorities will probably implement temporary road closures or detours in such locations. Officials could close mountain passes and tunnels as a precautionary measure during periods of intense snowfall.

The disruptive weather will likely cause delays and cancellations at airports across the affected region. Authorities will probably suspend port operations temporarily if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding/snow will likely block regional rail lines, causing freight and passenger train delays and cancellations.

Disruptions triggered by inclement weather and resultant hazards, such as flooding or avalanches, will likely persist well after conditions have improved - it could take days before floodwaters recede and/or officials clear debris. Repair or reconstruction efforts may result in residual disruptions if there is severe damage to infrastructure.