Christmas may see the arrival in New Zealand of an unwelcome guest in the form of Cyclone Yasa, the first tropical cyclone of the season.
While the country is set to bask under blue skies this week and in temperatures in the mid to high 20s, the promise of a sun-soaked Christmas day is looking sketchy.
The category 1 Yasa cyclone is currently in the Tropical Pacific between Fiji and Vanuatu where, according to Niwa meteorologist Ben Noll “it is expected to strengthen as it churns over the very warm ocean water, fuel for cyclones”.
The cyclone has appeared on the radars of both the US Global Forecast System (GFS), and the European Centre for Medium-Range Weather Forecasts (ECMWF).
“The 40 per cent confidence is based on modelling from various agencies over the past several days and reflects our current confidence,” Weatherwatch.co.nz said.
“The storm will be going through a major structural change at this point which means a number of future scenarios are possible from a serious major hit, to a real low that only brings some rain, to one that falls apart and misses New Zealand entirely.”
Noll, however, was more cautious.
He said both GFS and ECMWF produce forecasts across the whole globe in ranges of 10 to 16 days using satellites, planes and weather stations on the ground.
“Generally speaking, the forecasts are very reliable to three days, decently reliable for three to five days, after day five reliability can be anything from moderate to low.”
Noll said he believed Cyclone Yasa would remain in its current location for the next few days and at present was rated a category 1 for windspeed – at the lower end of the scale.
“Right now uncertainty is high. The chance of New Zealand to be impacted is low at this point but it’s worth watching.”
Noll also advised caution on the weather models as, “to the untrained eye, it may look daunting”.
“The forecast can change dramatically over half a day,” he said.
Noll also said the current La Nina climate pattern – which occurs when strong winds blow warm water at the ocean’s surface away from South America, across the Pacific Ocean towards Indonesia – did increase the risk of cyclone events hitting New Zealand.
“From a New Zealand perspective, [Yasa is] not something we should be worried about.”
For those closer to the cyclone’s current location, however, Noll said “absolutely it should be on your radar”.
What’s more, climate change is expected to bring more powerful storms and more severe flooding, as warmer temperatures make New Zealand’s climate more turbulent.
MetService tropical cyclone forecaster Raveen Das also cautioned about the reliability of long-term forecasting for events such as cyclones, and said another factor that made predictions complicated was the development of another cyclone near Samoa.
“That will have an impact on the likely track of Yasa,” he said.
“Two cyclones, that complicates things a lot.”
Both Noll and Das also said that by this Friday or early next week a much more reliable forecast of Yasa’s progress, and the possibility it could hit New Zealand, will be possible.