South Arm Forecast by Ben Matson (issued Tuesday 12th March)

Best Days: Wed: easing winds, early peak in W/SW groundswell. Fri: small pulse of swell with easing winds, best in the arvo. Sun: chance for a late pulse of sideband SW swell. 

Recap: Saturday’s strong groundswell coincided with light winds across the South Arm, but the swell was short lived and had eased significantly for Sunday morning as winds straightened up from the north. Similarly tiny conditions have persisted into Monday.

This week (Mar 13 - 15)

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No major change expected for the next few days. We’ve got a solid swell expected to kick in from late today, thanks to a powerful front/low travelling through the Southern Ocean over the last few days.

Although the synoptics look very impressive, this low is travelling a little more north in latitude than is ideal and this will impact size potential through the South Arm due to the associated W’ly component in the swell direction. For reference, we should still pick up easy 3-4ft sets at Clifton but protected spots will be significantly smaller.

This afternoon’s swell increase will be accompanied by gusty W/SW winds but the front will clear to the east quickly overnight, leaving us with lighter W’ly tending NW winds into Wednesday morning, allowing surface conditions to improve. An early peak in size is expected with a slow easing trend throughout the day.

Smaller surf and freshening NW winds are then expected on Thursday as a cut-off low approaches from the west (see below). This system also looks good on paper but its fetch length is short, and again its latitude isn’t great for the South Arm - it's simply riding too far north. I’m not confident we’ll see much surf from this system as a result, perhaps a brief peak on Friday with 1-2ft sets across the South Arm but the westerly swell direction significantly restricting surf potential inside Storm Bay.

The latest model guidance shows a brief intensification of this low as it passes under Tasmania on Thursday, with a S/SW fetch developing below the state, and this may provide a small flush of slightly bigger S’ly swell later Friday (perhaps 2ft+?) but confidence is not particularly high for any great waves. Friday’s winds will be rapidly easing post-frontal S/SW so conditions should be OK but perhaps slightly lumpy and wind affected early.

This weekend (Mar 16 - 17)

Friday’s swell will slowly ease through Saturday and Sunday. This will result in very small surf through the South Arm both days, clean under moderate N’ly winds.

An intensifying polar low well below WA on Friday looks like it’ll become quite intense for a period, and although poorly aligned, may generate  a small pulse of long period sideband swell for the South Arm, arriving late Sunday. You can see this swell on the period charts quite well but I don’t think there’ll be a lot of size but it’s worth keeping an eye on model updates. At this stage I wouldn’t be surprised if we saw a late pulse to 2ft+ on Sunday afternoon. I’ll update on Thursday.

Next week (Mar 18 onwards)

Nothing major on the long term charts at this stage though a steady progression of strong polar fronts and lows through the Southern Indian and Southern Oceans will maintain (at a minimum) persistent, pulsey small SW groundswells for the South Arm quite some time.