New Zealand: Heavy rainfall and strong winds forecast in parts of North and South islands through at least May 18

Event

A low-pressure trough is bringing heavy rainfall and strong winds to western North Island as of May 17. The Civil Defense Emergency Management office reported a tornado occurred in Waitara, causing minor property damage. The Meteorological Service of New Zealand (MetService) has forecast heavy rainfall, strong winds, and isolated thunderstorms through May 18. Heavy Rain watches are in effect for much of North Island, including Taranaki and Wellington, through the afternoon and evening hours. Rainfall could affect additional regions on North Island and northern South Island as the system moves eastward. Strong wind gusts of up to 90 kph (55 mph) are possible. A Strong Wind Warning is in effect for Tararua and Hawke's Bay south of Hastings through May 18; gusts of up to 130 kph (80 mph) are possible in these areas. Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change.

Hazardous Conditions
Periods of heavy rainfall could trigger flash 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. Strong winds could down trees or powerlines, causing power outages.

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 regional airports. Authorities may temporarily suspend port operations along the Tasman Sea, South Pacific Ocean, and Bay of Plenty 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 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. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

MetService