New Zealand: Severe weather forecast across western South Island through at least Jan. 20 /update 1

Severe weather is forecast across western South Island through at least Jan. 20. A series of fronts are forecast to bring periods of heavy rain in the affected area through early Jan. 20, while severe gale is possible in Fiordland Jan. 19. As of Jan. 18, the New Zealand National Meteorological Service (MetService) has issued the following weather warnings:

• Red Heavy Rain Warning (highest level on a three-tier scale): Westland. 60-80 cm (24-31 inches) of rainfall will likely accumulate about the ranges and 10-20 cm (4-8 inches) about the coast. The heaviest rain is forecast from early Jan. 19, with the heavy rain easing from the south early Jan. 20. Thunderstorms are possible. The rain could cause dangerous river conditions and significant flooding. Slips and floodwaters will likely disrupt travel, making some roads impassable and possibly isolating communities.

• Orange Heavy Rain Warning (middle level on a three-tier scale): Fiordland and Grey District. Rainfall of 20-35 cm (8-14 inches) is forecast.

• Yellow Heavy Rain Watch: Buller, headwaters of Canterbury lakes and rivers, headwaters of Otago lakes and rivers, and Tasman about and west of Motueka.

• Yellow Strong Wind Watch: Canterbury High Country and Fiordland.

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

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 stormwater drainage systems. Sites 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 heavy rain has saturated the soil.

Authorities could issue mandatory evacuation orders for flood-prone communities over the coming days. Disruptions to electricity and telecommunications services are likely where significant flooding or landslides impact utility networks.

Floodwaters and debris flows will likely render some bridges or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces will probably cause hazardous driving conditions on regional highways. Authorities are likely to close some low-lying routes that become inundated by floodwaters temporarily. Flight delays and cancellations at airports are probable.

Localized business disruptions are likely in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.