Weather: 'Above normal' risk of ex-tropical cyclone affecting New Zealand this season

Weather forecasters warn there's an "above normal" risk of an ex-tropical cyclone affecting New Zealand this season - and it could lead to severe weather and coastal damage again.

NIWA and MetService's assessment shows nine to 12 named cyclones are expected to occur in the southwest Pacific between November and April. At least three of these may be severe, reaching category 3 or higher.

On average, at least one ex-tropical cyclone passes within 550 km of New Zealand each year and for the coming season, the risk for an ex-tropical cyclone affecting us is considered higher than usual.

"The long-term average number of named tropical cyclones in the southwest Pacific (including the Coral Sea) is about 10 per season", says Chris Noble, MetService senior meteorologist and chair of the regional tropical cyclone committee.

"This season, cyclone activity is expected to be near or slightly above average."

Based on conditions in past seasons, modelling suggests at least three upcoming tropical cyclones will reach category 3 strength, with mean wind speeds of at least 119 km/h.

And NIWA says category 5 strength cyclones - where sustained winds exceed 199 km/h - have occurred in many years with conditions similar to what's coming up this 2021/22 season.

If an ex-tropical cyclone does come close to the country, there is a near-equal chance of it tracking to either the east or west of the North Island, and it could make landfall.

Significant rainfall, extreme winds, hazardous marine conditions and coastal damage are all possible - as Kiwis will remember from the trail of destruction left by 2018's Cyclones Fehi and Gita, which brought severe weather, storm surge and coastal inundation to parts of the country.

So, we're being urged to prepare for any developing cyclones or other severe weather that could strike.

"It does not take a direct hit or a severe cyclone to cause significant damage or life-threatening weather," says Noble.

"If severe weather is forecast, we urge the public to follow official advice from national meteorological services, disaster management offices or local Civil Defence."

If cyclones are expected to impact New Zealand with severe weather, official advice will be provided via severe weather outlooks, watches and warnings issued by MetService. Even if land areas aren't affected, warnings are still issued for vessels over the open sea.