thermalben

Plenty of swell on the way, but only a brief window of good winds

South Australian Surf Forecast by Ben Matson (issued Wednesday 21st October)

Best Days: Thurs/Fri: long period groundswell, with generally light winds and sea breezes on the Mid, prob some form of E'ly down south. Late Thurs PM for the most size. 

Recap: Building long period swells reached around the 4ft mark at Middleton on Tuesday, holding into this morning, though are now slowly easing. A temporary window of light NE winds Tuesday morning created clean conditions before SE winds developed through the middle of the day and into the afternoon, persisting overnight into this morning. The Mid Coast unfortunately didn’t see anywhere near as much swell as expected, which is a little unusual because we’ve had reports of great waves from elsewhere in the state that requires a reasonable degree of west in the swell direction (CdC buoy data says the swell direction was S/SW, which explains the no-show on the Mid). Wave heights maxed out at a slow 1ft Tuesday afternoon and have eased slowly today. Conditions have however been clean with light winds. 

This week (Oct 22 - 23)

*This week’s Forecaster Notes will be a little erratic as Craig’s on annual leave*

Alright! It ain’t the first time I’ve been skunked by the Mid (and probably won’t be the last) but nevertheless, the problem I now face is: how much confidence is there for the next groundswell?

It’s worth noting the following points:

1. Tuesday’s event was always the least confident of the two this week
2. The storm track is much better aligned this time around (though still positioned a very long way away)
3. Wave heights in West Oz this morning - from the swell we’re expecting in SA tomorrow - have come in a fair bit larger than Monday (as expected), which is also a very good sign. 

Because tomorrow’s swell is essentially independent from Tuesday’s - i.e. it needs to be treated on its own merits, instead of recalibrating because of anomalous upstream observations - I don’t think I’m going to change the forecast for Thursday.  

Thursday’s winds still look problematic for the South Coast. Although the tail of the ridge barely reaches the Vicco border - which may assist in creating pockets of lighter wind - it’s really hard to be confident we’ll see ideal conditions on what’s expected to be a building swell trend. Therefore, expect the worst and hope for the best. Exposed breaks across the Middleton to Goolwa stretch should pick 4-6ft by the end of the day (it’ll be much smaller earlier).

Along the Mid Coast, we’ll probably start off undersized, with the biggest waves showing late in the day as the swell peaks, by which time we may see a little more south in the wind. But, with size building to an inconsistent 2-3ft, there should be some fun waves across most breaks.

Friday morning looks to offer the best conditions of the two days with light variable winds and a gradual easing in size from Thursday’s late peak. However, an eastward tracking low pressure trough will advance across the region after lunch, bringing gusty S’ly winds to all coasts from about mid afternoon onwards. So, aim for an early session on either coast.

As a side note: ‘light variable’ wind means ‘from any direction’, which could be onshore. For Friday morning, it’s more likely this variable trend will hold from the east across both coasts (great for the Mid, not quite so great for Victor).

This weekend (Oct 24 - 25)

We’ve actually got quite a lot of groundswell on the way for the weekend, courtesy of a nice cycle of polar lows below the continent from tonight through into Saturday (see below). This is a great part of our swell window for the South Coast, as the more eastern storm track results in a little more south in the direction, which allows the energy to get into locations closer to Victor Harbor.

Conversely, it’s terrible swell direction for the Mid Coast.

In any case this is all irrelevant as local winds are going to create poor conditions anyway.

The western flank of Friday’s low pressure trough will maintain a gusty southerly influence across our region into Saturday, reinforced by a passing front to the south. A high ridging in from the west into Sunday will keep the wind at strength, and slowly veer the direction S/SE. 

This is a real shame (for Victor) as we’re looking at 3ft surf early Saturday building to 4-5ft through the afternoon, and holding into Sunday. 

Along the Mid Coast we’ll probably just see a small mix of local windswell and easing groundswell Saturday, becoming tiny into Sunday. It’s unlikely to be worth too much effort. 

Next week (Oct 27 onwards)

A developing high pressure system to our west will dominate our weather next week, with fresh SE winds Monday, easing Tuesday thru’ Thursday morning, but then restrengthening later Thursday and into Friday. This will maintain below-average conditions at Victor all week. 

At the same time, we’ll be under a spell of regionally small groundswell by this time, thanks to a synoptic blocking pattern upstream from this weekend onwards. Local S’ly windswells will still be punchy at Victor through Monday - though onshore with the SE breeze - and surf size will then quickly abate into the middle of the week.

Fortunately, there are some interesting developments for the long term.

An amplifying Long Wave Trough well west of WA next week will slowly migrate eastwards. Small long period forerunners from the Indian Ocean activity will grace our coastline from Thursday onwards, and the position of this system is ideal for the Mid Coast’s (long range) western swell window. So although no major size is expected during this time frame, Thursday onwards (in particular Fri/Sat) are on track for some fun waves on the Mid, local winds pending of course. 

And then, as the storm track shifts more favourably into our swell window later next week, we’ll start to see size prospects increase for the rest of the state for the following week.

More on this in Friday’s update. 

Comments

wiseautogas's picture
wiseautogas's picture
wiseautogas commented Wednesday, 21 Oct 2020 at 4:15pm

looks like the barrage of south easterly winds is with us for the next 4 or so months

john wise

Stef_Olly's picture
Stef_Olly's picture
Stef_Olly commented Thursday, 22 Oct 2020 at 5:36pm

Lol! A dozen scrapping over one foot Triggs #fknfacepalm

thermalben's picture
thermalben's picture
thermalben commented Thursday, 22 Oct 2020 at 5:48pm

Yeah a little underwhelming thus far (swell is still on the build), but a little bigger than one foot just over the channel.


Jay-Jay's picture
Jay-Jay's picture
Jay-Jay commented Friday, 23 Oct 2020 at 1:31pm

Building to 2-3 foot on the mid on Thursday ... what is this voodoo you speak of ?? 1 foot maybe with almost half hr wait between 2 wave sets.