• Auckland faces a risk of thunderstorms and a severe thunderstorm watch has been issued for Coromandel Peninsula, Waikato, Waitomo, Bay of Plenty and Rotorua.
• MetService warns of rising rivers, surface flooding, and difficult driving conditions in affected areas.
• Kiwis are advised to avoid swimming outdoors due to pollution risks from heavy rainfall.

Holidaymakers are in the firing line as a fresh round of severe weather watches and rain alerts are issued for parts of the country.

Kiwis are being warned to stay alert on Boxing Day as parts of the North Island face a severe thunderstorm watch, and other regions brace for heavy rain.

MetService has put the Coromandel Peninsula, Waikato, Waitomo, Bay of Plenty and Rotorua under a severe thunderstorm watch from 1pm to 9pm today.

The forecaster said there could be localised downpours of 25-40mm/h or more.

MetService forecaster Devlin Linden said areas between Auckland and the Bay of Plenty had a moderate thunderstorm risk throughout the day.

Linden said there was also a moderate thunderstorm risk for northern parts of the South Island between the afternoon and evening, which would pass by Friday morning.

Hawke’s Bay flooding risk, council staff called back from holiday

Heavy rain warnings have been issued for Gisborne and northern Hawke’s Bay, which are expected to receive between 120-130mm of rainfall between 7am on Thursday and 1pm on Friday.

MetService said this could result in rivers rising rapidly, surface flooding, slips and difficult driving conditions.

Linden said there was “reasonable confidence” heavy rain in the Gisborne and Napier areas would continue through the early hours of Friday.

Hawke’s Bay Regional Council told community members on Facebook it was calling back some staff from leave in preparation.

It said this would include staff on the ground in Wairoa closely monitoring river levels with a view to opening minor river mouths should the need arise.

“Currently, the Wairoa River mouth is performing well, and we will be closely monitoring the mouth during the period of high swell,” it said in a statement.

“From Esk to Māhia, we expect rivers to rise and remain within their channels, although we urge the community to be mindful that levels may rise quickly in heavy rain.”

The council said the ocean swell risk in Haumoana was assessed as low and back-up equipment was ready if needed.

“Across the Heretaunga Plains, rivers are expected to stay within their channels.”

Water quality warning

Land, Air, Water Aotearoa (Lawa) is advising New Zealanders to avoid swimming in waterways today because of the elevated risk of pollution in the water.

The organisation said there had been a significant amount of rainfall in the past 24 hours, and even swimming spots that usually had good water quality could become unsuitable.

Science lead Dr Elaine Moriarty said heavy rain washed contaminants from the land into rivers, lakes and coastal areas.

This runoff could bring bacteria from animal faeces, wastewater overflows and other pollutants into waterways.

“Conditions can change quickly, especially after a lot of wet weather, which is why we recommend avoiding outdoor swims for two to three days after heavy rain.

“If you swim in water that’s been impacted by pollution, you risk getting ill with symptoms such as vomiting, diarrhoea, respiratory infections, or eye, ear and throat issues.

Warning to motorists, severe gales forecast to hit

Severe gales in Wellington and on the east coast of the South Island were also expected during this time, Linden said.

Earlier, Hawke’s Bay Civil Defence Emergency Management Group posted on social media: “Sorry to be the Christmas grinch.”

“Make the most of the beautiful weather today, because Boxing Day through to Friday is looking a little less festive.”

A strong wind watch for coastal areas of Hawke’s Bay and Gisborne/Tairāwhiti has been issued from 1pm on Friday until the early hours of Saturday morning.

Southwest winds might approach severe gale forces in exposed places, MetService has warned.

New Zealand Transport Agency Waka Kotahi (NZTA) said people travelling over the holiday period must be prepared for challenging driving conditions and take precautions.

“Heavy rain increases the risk of slips and flooding, and strong winds mean drivers of high-sided and towing vehicles, and motorcycles must take extra care in exposed areas.

“Be ready for unexpected hazards and be aware that bad weather can see roads closed at short notice.”