La Niña: Flicking the switch
The switch is about to flick....finally!
Back in September, we mentioned the developing La Niña and how that would play out for weather and swell, and for that first half of spring the pattern held true.
Last month, however, the link was broken between the La Niña signal in the Pacific Ocean and Australia's weather and climate.
The main reason was that the subtropical high sat too far north across Australia, allowing cold fronts to steer up and across Western Australia, though deflecting south-east across the south-east of the country, drawing in heat from the north. November ended up being the hottest on record for the country, while rainfall was below average, especially for those coastal locations that are usually soaked during a La Niña spring.
North and east swells were also sporadic on the East Coast with weeks of south swell passing at a time. The South Australian coast and exposed Victorian breaks benefited though with swells from the west along with favourable winds
The MJO, or Madden-Julian Oscillation (a wave of tropical activity that propogates west to east around the globe), has also been subdued and stuck west of us, towards Africa.
As the MJO moves in across northern Australia we'll see a resumption of the classic La Niña pattern. The Southern Ocean storm track will shift towards Antarctica (known as a positive Southern Annular Mode), allowing the subtropical high to also shift south, bringing moist, onshore winds to the East Coast.
The combination of warm, moist easterly winds and tropical activity will bring wet weather to large parts of the country, but more importantly where it's needed across the north and north-east.
Below is the total rainfall forecast for the coming ten days, and while it shouldn't be treated as gospel, it's a good indicator for changing weather patterns.
As for surf, the subtropical high setting up camp across the Tasman Sea and then New Zealand will direct persistent easterly trade-winds towards the East Coast. Combine this with the odd embedded low squeezing the ridge from the north, and we're looking at an extended run of moderate to large easterly trade-swell.
Keep an eye on the regional Forecaster Notes for the finer details on timings, local winds, and sizes.