South by South West
Let me preface this article by declaring my personal opinion on south swells.
I hate them, well hate is a harsh word but let's say I strongly dislike south swells - especially those with a bit of west and longer period in them. The reason being that they mostly come in too straight, with any sets that do refract into our predominantly east-facing coast being ruler edge from headland to headland.
There are a couple of regions that respond well to such swells, and if you live on one of them you're probably shaking your head right about now, but for the most part, without a good pointbreak or south-friendly reef, you'll be trying to hunt out any kind of corner off the fast running sets.
With this in mind, expectations for the coming fortnight of southerly swell should be set on the lower end of the scale.
What is exciting is the scope, longevity, and persistence of a large Southern Ocean gyre that's currently developing across the south-east of the country.
As we transition from autumn to winter, the sun sits low in the sky to the north, and the sub-tropical high also shifts further north allowing cold fronts to project up from polar latitudes, across the country. The upper-level atmosphere is also playing a large part in steering and focussing the westerly storm track.
The upper level steering mechanism is known as the Long Wave Trough (LWT), and when focussed across a certain location, we see short-wave surface features (read: cold fronts) following a similar track. A pronounced northward intrusion of the Long Wave Trough is known as a node and these nodes move slowly around the Earth producing a pattern across the southern latitudes similar to a roller-coaster.
To the west of the nodes, cold air is advected up, north across the country, while to the east we see warmer, tropical air transported southwards.
One such node is currently sitting across Victoria, bringing heavy, widespread snow falls and a belting season opener, while on the coast we've got freezing winds and weather. However, the unique thing about this current node of the LWT is that it will remain strong and very slow moving, influencing the weather and surf across the south-east of the country for over a week.
The unusual prolonged nature is represented in the below chart, showing the Mean Sea Level Pressure anomaly (difference from the climate normal) for the coming week. Yes we expect strong cold fronts and lows at this time of the year, but the significance of the coming week is clear. As is corresponding the higher than normal pressure south of the country.
Currently, with its position across Victoria, we're seeing cold fronts projected up and across Tasmania, with the New South Wales coast copping side-band southerly swell energy.
However, as the node shifts slowly east through this week, the frontal activity will broaden and strengthen while projecting more favourably up through the Tasman Sea. When this happens, we'll see embedded polar fronts projecting up, one after the other on top of a very active sea state.
The result will be building levels of southerly swell across the East Coast, increasing in size and period with each successive frontal system. Stay tuned to Steve's Forecast Notes where he'll hone in on the specifics.
Currently the models are slightly misaligned regarding the position of the strongest activity throughout the weekend, with the European version having it slightly further west, resulting in less size pushing up through the Tasman Sea, but regardless we're looking at a sustained run of large southerly swell from Friday through to at least mid-next week, strongest and likely largest later Sunday and early Monday.
Locally, winds look to be generally favourable and out of the west owing to the northward extent of each successive front, providing plenty of quality options if you can avoid the closeouts. It should also set in motion northward flowing sand across the Mid North and North Coasts, a switch from the constant bombardment of easterly swells.
Looking further afield and the frontal activity will be squarely aimed towards Fiji, producing an extended run of large to extra-large surf throughout next week. Whether we see the size reach that seen during the Ramon Navarro swell in May 2018 depends on the alignment and strength of the frontal progression this weekend but early indications are that it will fall just below this size (peaking around 12ft).
Keep an eye on the comments section below as well as the regional Forecaster Notes for running updates on this prolonged southerly swell episode.