thermalben

Mixed options, though good conditions later in the week

Southern Tasmania Surf Forecast by Ben Matson (issued Monday 3rd May)

Features of the Forecast (tl;dr)

  • Plenty of surf all week, though wind affected at times on Tues, maybe Wed
  • Clean options Thurs/Fri as winds veer offshore
  • Another fun swell due Sunday with likely good winds
  • Solid surf next week, but wind affected

Recap

The weekend was small, with similar sized waves persisting into this morning. A new groundswell is starting to build across the region this afternoon as an unrelated southerly change envelops Southern Tasmania.

This week (May 4 - 7)

*Today’s Forecaster Notes will be brief as Craig is away*

Recapping Craig’s expectations for the new swell due later today, and the Cape Sorell buoy has recorded a jump in swell periods and wave heights since about late morning. However, as per the spectral trace below (snapshot from 3:30pm), we can see there are two main swell trains: (1) the primary at 20 seconds, with direction slight W of SW, (2) the secondary at about 7.5 seconds, with direction almost due south plus some mid-range energy in the 9-14 second range from the SW. 

The secondary swell from the south correlates with local winds off the Tas West Coast - the Cape Sorell AWS is unavailable, but Low Rocky Point (some distance south from Cape Sorell) has been recording S/SE gusts 20-30kts all day, which confirms the buoy's direction reading. Note: this information would be unavailable without spectral data (the regular buoy information shows a steady W/SW swell direction for the last 48 hours).

Anyway, this all means that the Hsig values are contaminated with a reasonable percentage of local S’ly windswell, and so the raw values should therefore be viewed cautiously - especially when considering the potential size range that Tp of 20 seconds might deliver.

All that taken into account, and also confirming visually the size of the (same) swell that reached Margaret River yesterday for the WSL with 12ft+ sets on offer at most reefs (bigger at offshore bombies), and I can’t really see any need to adjust Craig’s estimate for a peak in the 3-4ft range overnight, easing from 3ft+ on Tuesday.

As for conditions, today’s southerly change will clear to the north overnight, and an approaching front will swing winds to the W/NW, freshening through the day. So conditions will be OK early at open beaches but exposed spots will deteriorate. 

Moderate to fresh though easing W/NW winds will accompany a slow decrease in swell on Wednesday, with size around the 2-3ft mark. There’ll be waves on offer though there is a risk on local conditions.

Thursday and Friday look much better. An active frontal passage through the Southern Ocean all week should maintain 2-3ft across open beaches in the South Arm, with freshening N/NE winds as a deepening low pressure trough off the NSW coast and an approaching front from the west squeezes the pressure gradient. Set waves will be inconsistent but there should be some nice options on hand at the swell magnets. 

This weekend (May 8 - 9)

Early indications are for another long period groundswell to arrive this weekend - peaking Sunday - originating from the tail end of the current storm sequence in the Southern Indian Ocean, between Madagascar and Heard Island.

It’s expected to maintain strength as it passes through our far and mid-range swell windows over the coming days (see image below from Wednesday), and following a temporary easing trend on Saturday, should rebuild on Sunday into the 2-3ft range across the South Arm - the direction’s a little off-axis for Southern Tasmania so I’m keeping my size expectations in check (models only expect 2ft on Sunday as it is). 

As for conditions, a weak frontal passage may create fresh westerlies at some point - probably Saturday - but for the most part conditions are looking pretty good for Sunday with a pre-frontal N/NW flow likely to deliver clean conditions.

I'll firm up the timing and size specifics on Wednesday and Friday.

Next week (May 10 onwards)

There's no sign of any letup of the Southern Ocean storm track for the long term, though we may see less favourable conditions as it pushes closer to the region and thus has a more direct influence on our local winds. 

So, the first half of next week is on track for strong though very windy surf throughout Southern Tasmania. More on this in Wednesday’s update. 

Comments

Coorongkooks's picture
Coorongkooks's picture
Coorongkooks Tuesday, 4 May 2021 at 9:35am

Enjoyable read. Thanks for filling the void @thermalben.