2020 vision: The surf outlook for the next three months
- The next three months are very different compared to this time last year
- La Niña is developing
- Increased easterly swell for NSW and QLD, and more cyclones
- Favourable winds for the points and bays of N NSW and QLD
- Blocking pattern for Victoria and southern Tasmania
- Less long-period swell for Western Australia
As a keen weather watcher, a lot has come to pass since this time last year.
Hot off the back of one of the strongest positive Indian Ocean Dipole (IOD) events on record (with large cold water anomalies sitting off Indonesia and warm water piled up towards Africa), last September the global circulation pattern was disrupted to such an extent it reverberated into the upper atmosphere, causing a Sudden Stratospheric Warming (SSW) event over Antarctica.
This SSW - only the second significant event recorded in the Southern Hemisphere - then flowed back down through the lower atmosphere a month or two later. It caused a shift in the weather patterns across Australia and New Zealand through the second half of spring and into summer while also preventing the northern monsoon from properly developing.
A northerly shift in the westerly storm track (when it's usually contracting south towards the South Pole) brought dry westerly winds and record breaking heat, and in turn the worst bushfire season on record.
In terms of surf, the lower than normal pressure south of Tasmania generated fun swells and unseasonally clean conditions for the Victorian Surf Coast under the north-westerly winds, while these ruined what usually is the best time of year on the Mornington Peninsula.
At the same time, northerly winds plagued the south-east Queensland and northern NSW regions, while Sydney saw unseasonal westerly winds, clean conditions, and fun pulses of diffracted southerly swell.
Jumping ahead to this spring and we're seeing a developing La Niña starting to reach the thresholds needed for it to be official, and the opposite setup looks to be present for the coming few months.
What we know from La Niña is that the East Coast sees an increase in swell activity from the eastern quadrant, linked to instability in the Coral Sea from the build up of warmer water in the Western Pacific. This also results in more cyclones, but as we've discussed many times in previous articles on Swellnet, cyclones don't always produce the best swells. For that to happen, a cyclone must be cradled by a strong supporting high pressure ridge, which is discussed in more detail here.
The UK Met Office has just released its seasonal forecast for the coming three months (October, November and December) and what it shows that we'll likely see higher than normal pressure sitting just south of the Tasman Sea, extending just west of Tasmania and strongest just south-east of New Zealand.
Above this in the Coral Sea, lower than normal pressure is expected, linked to the developing La Niña.
There's also a slight indentation (lighter blue) on the forecasts across NSW and south-east Queensland, indicating a wind regime more from the east to south-east across these regions (not northerly), favouring the Gold Coast points and other protected bays.
With the higher than normal pressure extending under Tasmania and into Victoria's swell window, instead of the fun run of swell and westerly winds seen last year, we'll see more of a blocking pattern, hence less swell activity compared to normal and winds out of the eastern quadrant, favouring the Mornington Peninsula and Phillip Island.
If you live on the Apple Isle, focus your attention to the East Coast, with swells more likely from the north-eastern quadrant. The South Arm will be quieter owing to the blocking pattern.
Western Australia is tricky, with a continuation of mid-latitude systems more than likely, combined with a decrease in larger, long-range energy owing to a forecast increase in pressure across the south-western Indian Ocean, the main swell generating region. This will flow on to South Australia with less swell out of the south and more energy from the west.
As always, keep updated with the specifics for each region by subscribing to the thrice-weekly Forecaster Notes.