Analysing autumn 2021
Craig takes his seasonal review of the weather patterns during the previous three months.
And just like that, we find ourselves at the start of June, wondering where the last five months have gone.
A La Niña summer brought wetter, cooler, wetter across most of the country, and consistent surf for the East Coast, though less so the southern states. This was followed by an autumn which turned on across all parts of the country at alternating stages, though the contrast between months was stark as you'll see below.
The influence of the summer La Niña lingered across most surfable coasts into March with the southern states failing to see any major Southern Ocean frontal activity. Winds started to improve mid-March providing better options across exposed breaks in Victoria and South Australia, and with the subdued swell activity this was welcomed.
The East Coast saw a deluge of rain into the second half of March as troughy weather sat along the Dividing Range, drawing in moisture form the western Pacific Ocean and Coral Sea. The stationary nature of the pattern brought record rainfall to some regions, which, hitting an already saturated ground, resulted in widespread flooding and communities getting cut off.
There was plenty of surf out of the east, but surfing close to any river outlet was a risk with the large outflows, containing debris and pollution. North-east Tasmania saw pulses of S'ly swell through the first half of the month ahead of a great E/NE groundswell late month as a deep Tasman Low drifted slowly south-east through their swell window.
The chart below shows the Mean Sea Level Pressure anomaly for the month of March. The anomaly is the difference in pressure between the long-term climate average, with the blue and purple colours indicating that it was lower than the long-term average, while the yellow to red indicate it was higher. Keeping in mind that winds move clockwise around lows and anti-clockwise around highs you get a general idea of the setup through March.
What stands out is the low pressure anomaly siting across the eastern states and throughout the Tasman Sea, the vertically aligned low pressure anomaly spreading from the Indian Ocean south and the high pressure anomaly south-west of Tasmania, extending under the Tasman Sea and east of New Zealand.
The depression across the eastern states produced the aforementioned wet weather, while the high below Tasmania put a block across Victoria's south and south-western swell windows. That vertical depression west of Western Australia was a result of Southern Ocean storms projecting up into the mid-latitude's but then deflecting to the south-east on approach to the mainland, while tropical cyclones developed further north, closer to Indonesia and off the north-west of the country.
With the storms remaining at arm's length to Western Australia there were lots of clean, fun days of surf during March. April, however, hit the brakes, but more on this below.
Below is the Mean Sea Level Pressure anomaly chart for April, and what a contrast it is compared to March, especially for the southern states.
What's immediately obvious in April is the large, low pressure anomaly smack bang in South Australia's and Victoria's swell windows, and the blocking high south-west of Western Australia.
This is when the switch flicked for the Surf Coast, with an initial bombing low firing up through the early stages of the month, bringing very large surf to the reefs. Follow up mid-latitude and Southern Ocean frontal activity along with another bombing low provided endless days of pumping surf for the wave-starved state, though tapering into May.
South Australia also faired will with clean conditions and plenty of days at the deepwater reefs around Victor Harbor.
Western Australia went a little quiet owing to that blocking high, while Tropical Cyclone Seroja did the Do-si-do with another smaller cyclone before tracking south-east and making landfall across Kalbarri, bringing widespread damage.
The surf improved mid-to-late month as a secondary 'bombing' low and significant follow up system sent large S/SW groundswells north where they met favourable winds.
With all the action in the Southern Ocean, the East Coast only saw episodic pulses of short-range and longer-range S'ly swells.
In SE Queensland and northern NSW, April kicked off with a tricky east and south-east swell mix, as a complex low drifted south along the coast. Noosa pumped as did Kirra, but overall, it was locations south of the border that faired best, raking in the southerly swell energy once the east swell faded.
We then move onto May, and yet another switch in synoptic setups where, like March, the southern states go quiet while Western Australia and the East Coast fire up.
Looking at May's Mean Sea Level Pressure anomaly chart, we can identify high pressure spreading across the south-east of the country, with a low pressure anomaly still there south-west of Tasmania, albeit weaker, and a strong high south-east of New Zealand with two dips - one into the Tasman Sea and the other north-east of New Zealand.
So firstly, looking at the East Coast we saw the easterly swell window open back up with a mix of trade-swell from the western Pacific Ocean and stronger groundswell emanating from a deepening, broad low in the Tasman Sea early in the month.
The beaches pumped across the south-east Queensland and northern NSW coasts with endless days of peaky barrels, while further south, things got serious into the second weekend of the month with large levels of E/NE groundswell and offshore winds.
North-east Tasmania also faired well, with the swell lasting late into the following week ahead of a brief return to S'ly swell.
Late in the month we saw a tropical depression form into a significant low just north-east of New Zealand, generating a large E'ly groundswell to all East Coast locations on Tuesday the 25th of May.
This eased as trade-swell padded out the rest of the week ahead of another, less consistent E'ly groundswell which made landfall late Friday that week - though a large, building southerly swell episode was in full swing by then.
While the initial surge of southerly gales up the Tasman Sea last Friday and Saturday didn't provide much in the way of quality surf, it was a secondary intensification of severe-gale south-east winds (off the tip of New Zealand's South Island), projecting towards the country that provided the best surf.
A large, powerful SE groundswell made landfall on Monday, and along with offshore winds it sent pumping surf from Eden to the Sunshine Coast, tailing off slowly all week under light winds, bringing us up to today.
The southern states saw plenty of swell into the first half of the month, but winds failed to come to the party, being mostly onshore and strong out of the south owing to that high pressure anomaly sitting across South Australia. The end of the month offered better waves across most locations with fun swells and a shift to northerly breezes.
Margaret River saw slightly longer-range swells from storms firing up around the Heard Island region, then pushing east-northeast, generating large pulses of swells and with favourable winds due to a semi-permanent high setting up west-southwest of the state.
Which was lucky for the Wozzle, as they scored great surf for both events, while the energy has dimished since they left town.
Just to finish off, if we look at the three months of autumn as a whole we get the image below.
We can identify the low-pressure anomaly spreading south-west to south-east of Tasmania, supporting high east of New Zealand and lows north-east of New Zealand's North Island and in the Tasman Sea. But as explained and shown further above, the monthly breakdowns give a much greater idea on how the season played out, with periods of pumping surf mixed with average to poor conditions month to month, region to region.