The winter that was - 2020
Spring has sprung across most of the country and just like that, the endless run of pumping winter swells across the East Coast have come to a halt, right as the nor'easters kick in with precision-like timing.
The yin and yang of the surfing community was clear to see with calls of the "best winter in decades" ringing out east of the Great Dividing Range, while to the south it was "the worst August and winter in memory".
While Western Australia continues to cop stormy winter weather I've pulled up the charts to analyse the month just past.
As per the last analysis articles for June and July the main theme for the lack of winteresque swells is a pesky and persistent blocking high pressure anomaly bang across the normally active Southern Ocean storm track.
The term 'anomaly' means the difference from the 30 year climate average, and when observing a high pressure anomaly it indicates that the pressure was higher across that region compared to the long-term average.
Looking at the month of August (above) and what's clearly visible is a significant high pressure anomaly sitting right across Victoria's prime swell window, similar for Tasmania. South Australia was also affected, though westerly swells still arrived from under Western Australia.
The area where the anomaly sits is the main engine room for Southern Ocean storms and with the pressure reaching as high as 15hPa above normal through August, the cause of the poor run of swell is clear.
With such an anomaly of high pressure, the conveyer belt of polar fronts up and into Victoria usually seen in winter could never develop, instead blocked and steered away to the south once moving across Western Australia.
Countering this is the low pressure anomaly sitting south-east of South Africa, with Indonesia continuing to pump while Western Australia copped mid-latitude storms brought up from the south-western Indian Ocean.
Moving across to the East Coast and the dip in low pressure through the Tasman Sea is more pronounced than July, linked to the clustering of East Coast Lows from late July through mid-August. Things settled down from the middle of the month, bringing an end to the best run of conditions and swell for the Sydney region in over a decade, if not longer.
There's also the low pressure anomaly south-east of New Zealand, but the alignment of this in regards to the high north of it isn't actually favourable for Tahiti (for those interested).
If we look at the upper level winds at 500hpa (which influence the surface weather) you can see it splitting and weakening from a position south-west of Western Australia, right through to the Tasman Sea. Without this upper level forcing of westerly winds, there was no chance for the development of significant surface frontal systems and swell producing storms through the Southern Ocean.
Going beyond August I've pulled up the Mean Sea Level Surface Pressure Anomaly charts for the entire winter (below) and what it reinforces is the general state of play across the country.
Swell producing storms originating from the south-west Indian Ocean and winds from the northern quadrant for Western Australia with westerly swells, a blocking pattern for South Australia, Victoria and Tasmania (though South Australia still saw fun swells out of the west). Lower pressure through the Tasman Sea and another high pressure anomaly sitting east of New Zealand nurtured and prolonged any low forming off the East Coast, providing the endless run of swell for NSW and the east coast of Tasmania. Queensland was also decent though generally smaller than the better locations to the south.
Looking at the coming spring and summer, we're still on La Nina alert and this bodes well for an active summer of surf across the East Coast, but keep an eye on the tri-weekly Forecaster Notes for more details.