A summer like no other
Heralding in the new decade, things didn't seem quite right this summer: smoke-heavy days, headaches, sore throats, heat, and relentless fire. The constant sepia colour in the air became so normal that when sending photos back to friends overseas, I was oblivious to the brown tones until they pointed it out.
A myriad of factors influenced the southern states through early summer, that being the strong but weakening positive Indian Ocean Dipole (IOD) event, negative Southern Annular Mode (SAM) owing to a Sudden Stratospheric Warming (SSW) event which lifted the westerly storm track higher than normal.
The flow on effects of this were drier, hotter, and devastating westerly winds across our dried out country, compounded by the delayed monsoon (the latest arrival on record) again linked to the strong positive Indian Ocean Dipole event. This allowed heat to build up across central Australia, with long-standing temperature records smashed through South Australia, Victoria, New South Wales, and Queensland. It was the second hottest summer on record, coming in at 1.88° above average, the hottest being the summer previous.
This was on top of 2019 being the hottest year on record.
So what about the surf?
Across southern NSW there was a distinct lack of the normally strong north-east winds and lumpy, morning sick surf associated with it. The negative SAM events provided small but persistent pulse of S'ly groundswell through December with clean conditions each morning and fairly workable afternoon seabreezes. It seemed the smokey skies softened the diurnal heating of the land, thus suppressing the sea breeze.
January saw more swells from the east-northeast to north-east but without the associated winds and then the rain/humidity switch was flicked with a more normal return to wet summer conditions. Moisture finally arrived from the north and east, but the the intensity of rainfall was much greater than normal, with a significant deepening coastal trough delivering the biggest storm swell since the 2016 Black Nor'Easter on Sunday, February 9.
The heavy rains extinguished most of the fires throughout NSW, topped the dams back up but an unexpected side affect was the flushing of felled trees and debris into our major waterways, then being washed up onto the beaches with some resembling Canada or Oregon shorelines, crosshatched from the tide line to the foredune. Full length trees and branches provided added obstacles while surfing amongst the heavily polluted water and it just topped off what was quite the peculiar summer.
Tropical Cyclone Uesi provided another significant north-east swell less than a week later, jumping in size to 10-12ft on Friday the 14th. Uesi made an extra-tropical transition through the weekend, with large, pumping waves out of the east-southeast Saturday, followed by reinforcing south-east energy the following week. This topped off a great fortnight of waves in autumn like conditions ahead of a late return to summer drible.
Moving north and the south-east Queensland and northern NSW continued to be plagued by poor and strong winds form the north-eastern quadrant during December and January, linked to the negative SAM events shifting the sub-tropical high further north. This broke into February along with the rains, with consecutive days of heavy rainfall between 50-100mm+ and flash flooding across most areas.
The rains and change in weather patterns also brought a change in the swell patterns with lots of fun trade-swell throughout the month, mixed with standout days from Tropical Cyclone Uesi. We've ended the month with autumn like morning conditions and diffracted southerly swells.
One look at the wind anomaly through the summer period above shows the heavy influence the northerly winds played across south-east Queensland and northern New South Wales, strongly weighted by December and January.
Looking at February by itself and one can see a shift in the pattern to more normal easterly trade-flow.
Across the southern states the negative SAM events saw lighter and more favourable winds across the South Australian coast instead of the normal strong south-southeasters, bringing in scorching and record breaking temperatures. Much to the dismay of surfers across Victoria's Mornington Peninsula the Surf Coast offered the best conditions with fun swells.
This changed into February with a strong stationary high dominating South Australia bringing poor conditions to the South Coast, while better windows opened up across the exposed beaches in Victoria. As a result South Australia and Tasmania saw cooler than average temperatures through February, with Victoria about average. An early hint of autumn was seen over the last week in Victoria with pumping Surf Coast waves.
While the summer wind anomaly doesn't show up anything significant for the southern states besides a slight westerly bias across Tasmania, the February mean data (last diagram above) shows S/SE winds right across South Australia and edging into Victoria.
Moving over to the west and persistent and sometimes strong inland easterly winds brought with it record breaking heat and the second warmest summer on record for Western Australia, shown in the image below. This was only surpassed by last summer.
December offered clean conditions but no major swell until the Christmas break, with large pumping waves seen, and good surf continuing into the start of the New Year. Things started to settled down into late January and early February didn't really offer much in the way of swell, though during the middle of the month a flurry of cold fronts brought a good run of swell for a week or two. Things settled down into the end of the month along with fresh to strong morning offshore winds.
In ending, looking at this final chart, the Mean Sea Level Pressure Anomaly for the entire summer period shows the effect the negative SAM events had with lower than normal pressure spanning from the south of Tasmania across to New Zealand, shifted high pressure in the Coral Sea and then the low sitting along the East Coast, influenced mostly by February.