thermalben

Plenty of swell, but tricky winds abound

Victorian Surf Forecast by Ben Matson (issued Monday 12th October)

Best Days: Tues: strong though inconsistent groundswell, spoiled a little with onshore winds. Wed: good options east from Melbourne. Fri/Sat: another decent groundswell but potentially spoiled by local winds. 

Recap: Saturday punched a little higher than expected with 3ft+ sets across Surf Coast swell magnets, whilst Sunday came in a little underdone, easing rapidly to 1-2ft. Bigger surf was reported east of Melbourne (4-5ft easing to 3ft) and conditions were generally Ok with variable winds, though it did trend onshore both afternoons. Today is seeing a new swell build across the coast (2ft Surf Coast, 3ft east of Melbourne). It’s running a little late and should peak later this afternoon. Conditions are clean with light winds.  

This week (Oct 13 - 16)

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

I gotta say, of all the times to pick up the reins of the Vicco forecasting bench, this morning is the least desirable of the lot (having not looked at the Southern Ocean synoptics in quite a while). 

We’re right on the cusp of two interesting long period groundswells - the first of which is running late and thus presently undersized; the second of which is trailing close behind but was generated by an impressive cut-off low.

So, do I assume Friday’s prediction for 3-5ft surf west of Melbourne today and 6-8ft east of Melbourne is correct? Hindcasting this event won’t shed much light on the situation; invariably I’ll end up with the same result as Craig did. Ordinarily it’d be best to wait for the swell to fill in before recalibrating. But, I’m time-limited today, and it’s likely we’ll have a result in the hours following publication of this forecast anyway. So let’s crack on with it, eh?

Truth be told, whilst the parent systems that generated these approaching swells do look impressive, there are a couple of limiting factors. Today’s swell source was a very long way from the mainland (midway between Heard Island and West Oz longitudes), which means the enormous travel distance will shave off a lot of size and (more importantly) consistency. So even if we do reach the predicted size, set waves will be extremely infrequent.

The issue I have with tomorrow’s swell is that whilst the cut-off low responsible for the swell was very strong, and travelling in a manner conducive to a capture fetch, the actual fetch was relatively short and narrow, compared to a typical Southern Ocean front being driven by a core Polar Low. 

This somewhat weaksn my confidence. In my experience, these kinds of swells tend to favour a small number of spots where the magic numbers (size/period/direction) are optimal, but many locations usually miss out. 

So with this in mind, I’m going to pull back tomorrow’s size estimation and place a strong emphasis on the consistency of the swell (or lack thereof).

As it is, conditions won’t be great anyway, with a weak trough crossing the coast, swinging overnight northerlies to the west then the south. It won’t be terribly strong but these onshores will certainly take the sheen off an otherwise nicely lined-up groundswell.

Let’s peg exposed reefs across the Surf Coast in the 3-5ft range (smaller elsewhere), and expect very long breaks between sets. East of Melbourne should be very strong (though equally inconsistent) with 6ft+ sets.  

Wave heights will then slowly ease from Wednesday onwards and winds will veer E/NE - not too strong - but enough to cause issues across the Surf Coast reefs (very inconsistent 3-4ft easing to 2-3ft during the day). East of Melbourne will be a much better choice, with easing 4-6ft surf down to 3-5ft.

Wednesday may also see a minor SE swell across the Suf Coast (mainly west from Torquay) from developing easterly winds through Bass Strait Tuesday - though current expectations are that the fetch will be more E/NE in alignment, so we probably won’t see a lot of size. 

Thursday looks to be a bit of lay-day with early freshening N’ly winds ahead of a shallow W’ly change mid-morning in Torquay, and then around lunchtime across the Peninsula. We’ll be down to 1-2ft surf west of Melbourne by this time. If you’re lucky, east of Melbourne should have a brief window of small open beaches.

Friday has good swell potential but poor local winds. Over the coming days, a moderate though strengthening polar low near Heard Island will traverse the waters well below the continent, and from later Tuesday into Wednesday will start to project E/NE up into our swell window (see below). This is a great angle for the storm track, and so despite not being an amazing system, should generate a really nice groundswell for our region.  

The problem is that  a weak front will concurrently clip the coast overnight Thursday, delivering moderate to fresh S’ly winds. There’s a chance that a building high pressure may swing the wind to the east, but this will only favour open beaches east of Melbourne - and they may be overpowered with solid 6ft+ sets. West of Melbourne should come in around the 4ft+ mark by the afternoon.

I’ll firm things up on Wednesday.

This weekend (Oct 17 - 18)

There’s quite a bit of divergence regarding the weekend outlook.

A weak coastal trough expected to be near South Australia on Friday is unclear as to how it’ll evolve. We’ll either see a near-stationary ridge of high pressure extending west from Tasmania dominating the weekend outlook, maintaining moderate to fresh easterly winds - or, the trough will move slowly west, swinging the winds to the north ahead of a fresh W’ly change overnight that’ll maintain onshores throughout Sunday. 

However, either solution won’t provide any significant new swell for the state.

Saturday morning will see easing SW groundswell from Friday’s increase (3-4ft west of Melbourne, 4-6ft east of Melbourne, much smaller by the a'noon), so at this stage it’s looking like a poor start across the Torquay stretch.

We may also pick up some small SE windswell west from Torquay, thanks to Friday's developing easterly fetch through Bass Strait.

With some luck, the aforementioned coastal trough will influence local winds and allow open beach breaks to clean up through Saturday. 

I’ll take a closer look on Wednesday. 

Next week (Oct 19 onwards)

With the weekend outlook already divergent, there’s not a great deal of point in looking beyond into next week, as it’ll all change quite a bit over the coming days. 

See you Wednesday!

Comments

thermalben's picture
thermalben's picture
thermalben Monday, 12 Oct 2020 at 11:28am

Clean straight lines building across the Bellarine. Still a ways to go though.

thermalben's picture
thermalben's picture
thermalben Monday, 12 Oct 2020 at 1:32pm

Super inconsistent, but the lines are slowly building.

ringmaster's picture
ringmaster's picture
ringmaster Monday, 12 Oct 2020 at 2:53pm

Mid week surfs (especially mid morning to mid arvo) are SO much more fun than weekends!

Had a real fun surf thru low tide today with never more than 6 or 7 out. Woulda been a different story if it was yesterday..........

Walk around G's picture
Walk around G's picture
Walk around G Tuesday, 13 Oct 2020 at 7:44pm

Sooo....rim-master, low tide (check), mid morning to mid arvo (check) = super quiet (check)....ok
I won't tell anyone else, I promise...

ringmaster's picture
ringmaster's picture
ringmaster Tuesday, 13 Oct 2020 at 8:58pm

It's no secret. Everyone would love to surf at those times but plenty can't.

That's why it's so good.

willibutler's picture
willibutler's picture
willibutler Tuesday, 13 Oct 2020 at 9:49pm

The water has dramatically warmed up since the easterly, was semi cold in a 4/3 3 days ago like numb feet and brain freeze going in but tonight was comfortable in a very worn out 3/2 anyone got readings on the change in water temp.

thermalben's picture
thermalben's picture
thermalben Wednesday, 14 Oct 2020 at 7:15am

Point Nepean water temp is still around 14 degrees. Which coast were you at? 

willibutler's picture
willibutler's picture
willibutler Wednesday, 14 Oct 2020 at 7:49am

Surf coast. Everyone in the water agrees round here

Cyclist_123's picture
Cyclist_123's picture
Cyclist_123 Wednesday, 14 Oct 2020 at 11:32am

It was definitely noticeable at 13th

Walk around G's picture
Walk around G's picture
Walk around G Wednesday, 14 Oct 2020 at 4:48pm

Yeh you might be onto something there willi b, looks like a sudden significant change in water temps early October, within the Bay at least. I can't find an anomaly chart for the strait though?
http://www.baywx.com.au/baytemp_meanmedian_thisyear.png

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 14 Oct 2020 at 5:24pm

Middle of bay is a bot diffrrent though no?

Walk around G's picture
Walk around G's picture
Walk around G Wednesday, 14 Oct 2020 at 5:42pm

Yeh probably, check this graph out NB.

http://www.baywx.com.au/baytemp_meanmedian_diff.png

I not sure but I assume the bay gets cooler than the ocean in winter due too all the cold freshwater run-off and is warmer in summer from solar heating on the relative small body of water and due to lack of offshore currents/upwelling etc.

Ben, do you have any thoughts regarding the temperature variations/graph?

goofyfoot's picture
goofyfoot's picture
goofyfoot Wednesday, 14 Oct 2020 at 7:48pm

wag yes the bay gets colder and warmer than the ocean as its a smaller body of water as you mentioned. not sure fresh water run off has much to do with it but someone much cleverer than I on here will correct me if I'm wrong

willibutler's picture
willibutler's picture
willibutler Wednesday, 14 Oct 2020 at 8:04pm

nothing to do with the fresh water run off just basic physics about how its a smaller body of water so cools down quicker too due to the thermal inertia

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 14 Oct 2020 at 8:15pm

Just ask Urbnsurf

Walk around G's picture
Walk around G's picture
Walk around G Thursday, 15 Oct 2020 at 5:53pm

You're spot on mate, mystery solved. Thanks

Bnkref's picture
Bnkref's picture
Bnkref Wednesday, 14 Oct 2020 at 8:18pm

Craig did an article on it recently. There was a handy graph in it which showed the difference between the temps in the bay and the ocean.

https://www.swellnet.com/news/swellnet-analysis/2020/08/18/seeking-heat-...

Walk around G's picture
Walk around G's picture
Walk around G Thursday, 15 Oct 2020 at 5:51pm

Wow, thanks for the link. Somehow I missed that article, interesting stuff :)

greyhound's picture
greyhound's picture
greyhound Wednesday, 14 Oct 2020 at 8:46pm

VIC ports . Then click wind waves and weather. For pt Nepean wave bouy that is..
I find this site really useful..current temp taken every half hour.. not sure about yearly trends though..
great For swell info.. trending up/down, period, direction etc etc.

willibutler's picture
willibutler's picture
willibutler Wednesday, 14 Oct 2020 at 9:03pm

the buoy doesn't actually show direction

greyhound's picture
greyhound's picture
greyhound Thursday, 15 Oct 2020 at 8:49am

Currently from 205 degrees.

willibutler's picture
willibutler's picture
willibutler Thursday, 15 Oct 2020 at 9:30am
greyhound's picture
greyhound's picture
greyhound Thursday, 15 Oct 2020 at 11:35am

Yeah I remember that article. But in general terms.. tells you what direction.. you could split hairs on every bit of info on it..