Six feet to twenty feet, and everything in between. 

Every refresh of the East Coast forecast charts reveals a new outlook, and it all surrounds the movements of Tropical Cyclone Alfred.

Alfred is currently a Category 3 system, meandering in the Coral Sea, triangulated midway between the Australian mainland, the Solomon Islands, and New Caledonia.

While there’s high confidence regarding the southward movement of Alfred over the coming days, this confidence lowers significantly into the weekend with multiple scenarios at play, including a coastal crossing between central and southern Queensland, which, if it were to happen, would be devastating.

Current position of Tropical Cyclone Alfred (Zoom.Earth)

With so many advances in computing and forecasting technology, why are tropical storms still so hard to grapple?

The answer to that is largely because cyclones survive in environments where there is weak upper atmospheric wind. Yet it's also those upper atmospheric winds that steer cyclones.

While the cyclone itself contains signficiant winds, where and how fast the whole system moves is is dictated by other, often more subtle, environmental factors. These include ridging from high pressure or interactions with the jetsream.

When there's an absence of those environmental factors, a powerful system is at the mercy of hairline shifts in the atmosphere - and that creates a forecasting difficulty.

Since forming last weekend, Alfred has meandered about the Coral Sea thanks to the lack of any major steering influences.

The track over the next couple of days will be a result of a subtropical high in the Tasman Sea, moving east across New Zealand, with Alfred following the path of least resistance south and settling at a position east of Rockhampton this weekend.

The circuit breaker for whether Alfred stays offshore from the coast or moves inland - and hence whether there will be surf or just a rainy washout - is an approaching upper level trough from the south-west on Monday.

Importantly, this trough will, for the first time since Alfred formed, bring upper level steering winds. The winds will be north-west and arrive ahead of the trough, helping steer the system away from the coast. Yet any delay in the approaching trough would allow Alfred to possibly start tracking inland.

The below chart shows the timing of the expected upper level trough, with The European Centre for Medium-Range Weather Forecasts (ECMWF) having the trough arriving earlier and with more strength (left) than the US’s Global Forecasting System (GFS) forecast (right). This can be seen by identifying the trough line axis, which is across Coffs Harbour in the left image on Monday evening, but still around Newcastle in the right image.

Timing of the upper level wind change Monday evening. ECMWF (left) has it arriving earlier and with more strength than GFS (right). (Weatherzone)

While only hours in diffference, any weakening or change to the angle of this trough could be the difference between a coastal crossing and an offshore track.

Looking at the associated track forecast by various iterations of the ECMWF model for TC Alfred (below) and the majority of the forecasts have it tracking south-southeast, away from the coast into early next week. There is still a chance for a coastal crossing as indicated by the lighter green across south-east Queensland and northern New South Wales, though it puts this at 10-20%.

Tropical Cyclone Alfred strike probability (ECWMF)

In regards to swell potential, the most beneficial for surfers is for TC Alfred to stay out to sea, at arms length of the coast. This would generate a wider ranging swell event from Queensland to southern New South Wales with less ‘bank-busting’ surf that otherwise would only be surfable at a handful of breaks.

In terms of coastal erosion and impacts on the general population, this is obviously the best case scenario as well.

While the offshore outlook is favoured, we’ll continue to ride the roller coaster of model updates as the eventual track and swell potential becomes clearer.