South Arm Surf Forecast by Ben Matson (issued Friday 13th May)

Features of the Forecast (tl;dr)

• Small surf and gusty winds from Sat thru' Mon
• Building swells Tues/Wed but with westerly gales
• Better swell direction by Thurs but winds will probably be SW
• Smaller, cleaner next Fri
• Small period next weekend onwards

Recap

W’ly swells have maintained very small wave heights through the South Arm over the last few days, though it’s been clean with light winds.

This weekend (May 14 - 15)

We’ve got a very windy period coming up as a strong conveyer belt of fronts cycles through the Southern Ocean. However, Saturday and Sunday look relatively benign with just 20kts out of the northern quadrant.

Unfortunately, the current westerly swell cycle - that’s not really making much of an impact in the South Arm anyway - is easing back in size, and will thus maintain very small surf conditions. Keep your expectations very low.

Next week (May 16 onwards)

We’ve got an incredible synoptic chart developing at the moment. 

A series of powerful fronts will race through the Bight on the weekend, of which the parent low is a complex beast, already beginning to undergo cyclonegensis in a few regions, as a polar low (off Antarctica, south of WA) and a cut-off low in the western Bight.

These lows will coalesce to form a large primary system by Sunday, but the resulting swell will still be too westerly for the South Arm on Monday. 

As such, we’ll see a continuation of very small surf conditions with NW tending W’ly gales as more fronts cross the coast.

Westerlies will continue to hammer the coast into Tuesday, but we’ll see a better aligned W/SW tending SW swell build in size, towards a peak on Wednesday.  This will originate from a powerful front wrapping around the northern flank of the primary low, late Sunday into Monday (see below).

It’s hard to be totally confident on surf prospects, as wave heights will still be heavily attenuated in Storm Bay, relative to exposed, or more favourably aligned coasts, which will be very big - for reference, we’re looking at 10ft sets at the Victorian Surf Coast, which is not common.

So, I still fear we’ll suffer in the size department with peak surf size holding around a windy 3-4ft+. This would be fine under slack winds, but the wind really makes it hard to be enthusiastic.

Once the associated Long Wave Trough moves further east, and trailing fronts slide up into the Tasman Sea, we’ll see a better aligned storm track through our swell window (say Tues/Wed, resulting in Wed/Thurs surf) but the problem is that local winds will also veer to the southern quadrant around the same size. And there won’t be enough size for protected points.

Add in the significant wind chill factor and next week is shaping up to be a blustery round of mediocre surf, certainly an outlier to what’s expected elsewhere throughout the southern states.

Looking further ahead, and Thursday’s SW swell will ease into Friday with light winds, and small surf from next Saturday onwards may precede an extended period of minor swells thanks to a blocking pattern upstream diverting Southern Ocean fronts away from our swell window.

Have a great weekend, see you Monday!