Extended Forecast: Late August to Mid-September
Over the past twelve months, Craig has published a regular series of articles looking back at monthly and seasonal weather patterns. These articles offer hindsight data, explaining the surf patterns for each stretch of Australian coast during the period in question.
Informative, no doubt, but not as useful as a forecast.
Fortunately, the European Centre for Medium Range Forecasting (ECMWF) provides some great tools, publishing bi-weekly Mean Sea Level Pressure anomaly charts for the upcoming period. Each forecast chart spans a week, showing the chance of higher/lower than normal sea level pressure for that week.
This gives us a rough idea on what to expect for swell and wind for each region. It's most useful when extending our gaze beyond the week ahead - which is comprehensively covered in our Forecaster Notes - out to two and three weeks hence.
Looking at the coming week, Monday the 23rd to next Monday the 30th, and what stands out is the low pressure anomaly sitting off the southern NSW coast, the strong high east of New Zealand (with a low squeezing it from the north), and the low pressure anomaly spreading from the Heard Island region up into the Bight.
What we can quickly gain from this is that the southern NSW coast will be influenced by a strong and slow moving low pressure system (currently forming now) bringing an extended run of large surf, while further north, some fun, distant E/SE trade-swell is due from the setup east of New Zealand.
Victoria is squeezed between the low off the southern NSW coast and high south of Tasmania, bringing onshore winds which improve as you head towards Adelaide. The drawn out low pressure from Heard Island up towards Western Australia will see strong polar fronts steered up and through this region, accompanied with onshore winds though due to the low pressure anomaly enveloping the coastline.
The position of the light blue shading through the Bight also indicates that frontal activity pushing east through it will be high riding and not overly favourable for swell production once moving across the country.
If we then look at the second week which covers from next Monday the 30th of August through to the 6th of September, we see a much more favourable setup for Western Australia, South Australia, and Victoria, but less so for the East Coast.
A broad and expansive low pressure anomaly sitting south of the country points to a strong swell-generating frontal system pushing up and under the Bight, though dipping south-east on approach to Victoria, bringing favourable winds from the north to north-western quadrant. Swells will arrive from the west for Victoria but with northerly wind it's an ideal set up.
This wind regime looks more north-west across South Australia, while the Western Australia coast looks to see swells more from the south-west and with more favourable winds owing to less of a dominating synoptic setup. Looking into week three and seeing a high pressure anomaly moving in (detailed further below), one can bet on improving winds through the second half of the week (start of September).
Looking over east and unfortunately the dual high pressure systems aren't ideal for swell production with southern NSW likely to drop back in size and expecting a slower period of surf, with more northern regions possibly seeing some small E/SE trade-swell from the top of the highs.
Moving out to week three, Monday 6th of September to the following Monday, the 13th, our confidence falls away, however, we can see that high moving into the south-eastern Indian Ocean which will quell any major storm generating activity for Western Australia. It will bring a favourable run of offshore winds though, while the low south of Tasmania looks to produce S/SW-SW swells for South Australian and Victoria with favourable conditions.
The East Coast is a little tricker but with the high setup as it us, small levels of trade-swell could be seen across south-east Queensland and northern NSW but with less favourable winds from the northern quadrant. Southern NSW remains a mixed bag, but it'll be great to watch how everything pans out into the middle of September.