South Arm Surf Forecast by Ben Matson (issued Wednesday 13th September)

Features of the Forecast (tl;dr)

• Small and clean Tues
• Small new swell Wed/Thurs but with very windy conditions
• Small surf then persisting Fri thru Tues; light winds by Sun
• Windy pattern with possible swells to resume mid-late next week onwards

Recap

Saturday played out as expected with tiny surf across the South Arm, however Sunday delivered more size than forecast (inconsistent sets around the 3-4ft mark at exposed South Arm spots), which persisted into this morning. However, conditions have been extremely blustery at times; wind gusts at Maatsuyker Island reached 78kts (or 145km/hr) in the early hours of Sunday morning; more locally, Dennes Point reached 43kts (80km/hr) early Sunday. The best explanation for the over-performance of this swell is probably due to three factors - (1) the swell direction not having as much west in the regional direction as anticipated, and (2) swell size and periods coming in a little bigger than modelled (some regional buoys recorded Tp of 20 seconds overnight Saturday), and (3) an impressive captured fetch through the southern Bight, which I failed to pick up in my analysis.

This week (Sep 19 - 22)

We’ve got another active week of wind and weather ahead, with the Southern Ocean still quite busy with a powerful frontal conveyor belt pushing under the continent.

We’ll see slowly easing size across the South Arm into Tuesday with freshening N'ly winds, and slow 1ft sets at most beaches, maybe some stray 1-2ft sets at swell magnets. Winds will veer NW throughout the day.

The first of several large westerly swells will reach the Tasmanian region on Wednesday in sync with westerly gales. Although I’m now a little gun-shy on downplaying size prospects from westerly swells, given what eventuated over the weekend, the storm track is a little different this time - further north through the Bight, and aimed away from Southern Tasmania (see below) - and I think it'll remain on the smaller side of the coin in Storm Bay. Add in the blustery conditions and it's looking like another average day for surfing.

Winds will back to the SW in the wake of the main front on Thursday and this will coincide with a peak in swell, maybe some stray 2ft, possibly 2-3ft sets but with very average conditions. A late swing back to the west is possible so western ends may have small options into the afternoon. 

Smaller, easing swells are then expected into Friday with winds reverting back to the W/NW and strengthening as another front approaches from the west,

In short, it's looking to be a small, windy week across the South Arm.

This weekend (Sep 23 - 24)

We’ve got two minor new swells for the weekend, in addition to small easing swells from Friday.

The first new groundswell will probably make landfall at the buoys on Friday, with extra long peak swell periods (22-23+ seconds, generated by the phenomenal storm below South Africa over the last few days (see article here). Suffice to say, the enormous travel distance means we won’t see much size across Southern Tasmania (the swell is better aimed into Indonesia, we are merely receiving small sideband energy).

The second swell will have been generated by strong but still-distant storm activity WA of WA, near Heard Island at the moment. It’s actually sourced (mainly) from NW gales ahead of a deepening low, but we’ll see the swell energy curve back through the Great Circle path into the Tasmanian region, but this is a flukey swell source for Storm Bay so I'm not confident on there being much size.

Locally, conditions look good both days , with moderating W/NW winds on Saturday and light variable winds Sunday. However, don't expect much size.

Next week (Sep 25 onwards)

Similarly light winds and small swells are expected early next week, before the frontal cycle spins up again from about Wednesday or Thursday onwards. It's too early to pin down specific swell events into the long term, but there's certainly some potential for a return to wintry waves later next week and into the weekend. 

See you Wednesday!