Two big climate drivers that have stoked Australia's wildfire catastrophe are finally about to fade, according to Niwa's latest long-range forecast. Photo / Getty Images
Two big climate drivers that have stoked Australia's wildfire catastrophe are finally about to fade, according to Niwa's latest long-range forecast. Photo / Getty Images
Two big climate drivers that have helped stoke Australia's wildfire catastrophe are finally to fade out, according to Niwa's latest long-range forecast.
The exit of a long-positive Indian Ocean Dipole (IOD) and a long-negative Southern Annular Mode (SAM), will also leave New Zealand without a single big influencer to messwith our weather over the next three months.
In its seasonal outlook, released today, Niwa picked a mixed bag of temperatures and rainfall for the country between now and March.
But the biggest change was a switch in states of the IOD and the SAM, which have both held sway over weather on both sides of the Tasman over recent months, and primed eastern Australia for disaster.
The IOD is a seesaw-like system that typically had three phases - neutral, positive and negative.
In a positive state, it created a temperature difference across the tropical Indian Ocean, with cooler than normal water in the east and warmer than normal water in the west.
For Australia, that spelt dryness – as did a negative phase of the SAM.
The SAM - effectively a ring of climate variability encircling the South Pole - usually brought lower air pressure over New Zealand when in a negative phase, increasing the chance of westerlies and unsettled weather.
Across the Tasman, a negative SAM was known to shift westerly winds toward the equator and Australia, meaning less moist onshore flow from the east, and therefore bringing less rainfall over eastern Australia.
Scientists have also pointed to the hidden hand of climate change, which was especially causing IOD events to become stronger and more frequent.
Over the next three months, the SAM was expected to switch to neutral, while the IOD's powerful positive phase was now also flipping back to neutral.
Niwa also expected the tropical Pacific to remain in an El Niño-Southern Oscillation (Enso) neutral state over the period, leaving New Zealand without any strong and persistent climate drivers to flavour its weather.
Source / Niwa
Its outlook picked temperatures to be near or above average for all of the North Island, near average in the north and east of the South Island, and near or below average for the west of the South Island.
Air pressure was forecast to be lower than normal to the west and south of New Zealand, with higher than normal air pressure north of the country.
This was expected to come with a westerly to south-westerly air flow – but the door was still open for periodic northeasterly winds to sweep in, especially during February.
Rainfall was projected to be near or below normal for the north of the North Island, above normal to normal for the west of the South Island, and normal elsewhere.
But Niwa forecaster Ben Noll said there was the possibility of more active conditions in the tropics later in the season bringing a cyclone-driven soaking to New Zealand later in the season.
Niwa has forecast the usual one ex-tropical cyclone coming within 550km of New Zealand, potentially bringing heavy wind and downpours.
"But, because we are on the verge of a pattern where it's potentially going to become more active, I'd definitely impress upon people to not let their guard down, because as we saw two years ago, we had three tropical cyclones come near our coastlines."
In the shorter term, Noll said a large high pressure system was expected to move toward the country around the middle of the month, bringing warm weather.
