Victorian Surf Forecast (issued Wednesday 12th February)

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thermalben started the topic in Wednesday, 12 Feb 2014 at 4:58pm

Victorian Surf Forecast by Ben Matson (issued Wednesday 12th February)

Best Days: Thurs: open beaches east of Melbourne.

Recap: Mainly small waves with early E’ly winds tending S’ly throughout the days. A new long period groundswell arrived this morning (detected at the Pt Nepean buoy just after 8am), but it’s been slow to build. However Cape Sorell is showing an upwards trend and we’re looking at a full day of waves tomorrow as the bulk swell energy moves through.

This week (Feb 13-14)

No major deviation away from expectations for the Thursday outlook. We’ll see moderate E’ly winds and an inconsistent, long period groundswell that’ll mainly favour the open beaches east of Melbourne with 5-6ft+ sets at times (expect long breaks of smaller waves between sets). These east winds won’t do many favours for the Surf Coast so expect average surf west of Mebourne.

A broad low pressure trough west of the state will move eastwards into Friday, bringing about a prolonged period of gusty southerly winds for the region. Apart from a brief window of opportunity in the morning (when winds will be onshore, but much lighter in strength), Friday’s surf potential will be significantly reduced - we’ll be on the backside of Thursday’s swell event anyway - so keep your expectations low.  

This weekend (Feb 15-16)

Although the broad trough will clear to the east early in the weekend, an approaching front (with a pre-frontal trough for good measure) will move across Bass Strait on Saturday, reinvigorating fresh onshore winds about all parts of the coast. Currently model guidance has these onshore winds being amplified on Sunday as a low pressure system develops off the NSW South Coast. 

This is a shame, because the low attached to Saturday’s front - and indeed another low just prior to it - are expected to generate plenty of swell for the coast (although, not quite enough for those protected spots that can handle strong S’ly winds). So right now I’d flag the weekend for waves. But, check back on Friday to see if the models have wound back this scenario and opened up a window of opportunity.

Next week (Feb 17 onwards)

A high moving in from the west will clear the weekend’s southerlies, but will also block the swell window, leading to small surf through the first half of next week. A series of fronts backing up behind this look to be our next major source of swell, with a current ETA around Wednesday or thereabouts. However at this stage no great surf is expected from it. Tune in on Friday for more details.

gbprophoto's picture
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gbprophoto commented Thursday, 13 Feb 2014 at 4:13pm

I'm confused. The Phillip Island forecast says Saturday morning will be ENE yet in your report here for Victoria you're saying it's going to be onshore.
Which one is it?

thermalben's picture
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thermalben commented Thursday, 13 Feb 2014 at 5:54pm

GB, that's a good question with (unfortunately) a complex answer.

Firstly, our forecast graphs are 100% computer generated. They're updated four times per day and show raw computer model output with no quality control. 

The forecast notes (written above) are a personal interpretation of the raw forecast data, using the most update-to-date weather information available on Wednesday afternoon (since then, the computer models have updated another four times, and may or may not have changed the data for the weekend's forecast).

As such, it's always possible that things could have changed. In fact more times often than not, the models will change as soon as a written forecast is published. It's the eternal curse of the surf forecaster.

But, the the current weather situation is very interesting and also needs to be brought into the picture. Right now we have a broad, complex trough of low pressure moving from west to east across the entire continent. Low pressure surface troughs are amongst the more difficult weather systems to predict (with regards to local winds), because their characteristics are mainly surface related, are not directly steered by upper level winds (which tend to follow more predictable paths). When a low pressure trough is in the vicinity, local winds often do weird and unusual things. And computer models often struggle to get the forecast details right.

This weekend's forecast is consequently quite tricky. It's worth noting that up until 45 minutes ago, the BOM had a similar outlook as per my Wednesday forecast (their forecast for this Saturday - visible on their website until very recently was "Southeasterly 10 to 15 knots turning south to southwesterly 15 to 20 knots during the morning").

However, the BOM updated their forecast at 4:52pm this afternoon, to reflect a change in the model output since yesterday: "East to southeasterly 15 to 20 knots shifting south to southwesterly in the afternoon". A quick visual scan of the latest weather model data confirms this change.

So - what this tells me is that the computer models have slowed the eastward progression of the trough, delaying its arrival in Victoria until Saturday afternoon, and opening up a small window of clean waves east of Melbourne in the morning. I'll update my notes accordingly tomorrow. That is, as long as the models don't swing the other way and speed up the trough again...

Sorry for the overly descriptive analysis - however this gives a quick peek into the ever-changing routine that Craig and I do all day, every day, for every single forecast region.

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indo-dreaming commented Thursday, 13 Feb 2014 at 7:32pm

Okay, that explains why even on the actual daily forecast the predicted winds were wrong, predicted E-NE today but even early was very very light SE to SEE most of the day also got it wrong on the swell, bit smaller than predicted.

But that said its rare that you guys get it wrong, easily the most accurate of all the forecast sites.

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carpetman commented Thursday, 13 Feb 2014 at 8:04pm

Hey Ben,

It's probably on your to do list but can you add the model run times to the forecast pages? It's handy to know how fresh the info is.

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thermalben commented Thursday, 13 Feb 2014 at 8:41pm

ID - yeah these troughy patterns are a real pain with the local winds sometimes. And the models can't resolve the local features very well either, which exacerbates the problem.

CM - yep it's on our to-do list (actually, the run time is in the page source if you search for the text 'debug'.. We've just gotta get it up where its nice and easy to read). Generally 00Z - the most reliable of all of the model runs - is available by about 4:40pm each day.

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southey commented Thursday, 13 Feb 2014 at 10:46pm

i surfed good waves yesterday and today . And the BOM / access model guidance inc. SN was pretty close to spot on for where i was .....
As Ben has mentioned its almost critical that you look @ current local obs ( no offence , but i like to use BOM for these ) as you can check whats happening around you 150 k's or more in all directions including inland for an up to date idea of exactly whats moving where . The large Trough expanse , lines and cut off in this system has made it quite dynamic . And any time you have a Tropical system entering down into to the mid lattitudes its best not to trust model guidance 100% . But watch it evolve .... The bonus is you'll be onto before most and have your surf done and dusted when others show up scratching their heads and suiting up .

" SA's Reserve Capacity "

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donweather commented Friday, 14 Feb 2014 at 7:18am

thermalben wrote: Generally 00Z - the most reliable of all of the model runs - is available by about 4:40pm each day.


Is this AEDST Ben?
thermalben's picture
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thermalben commented Friday, 14 Feb 2014 at 7:19am

Yep (ie Sydney time).

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Craig commented Friday, 14 Feb 2014 at 11:26am

Just to clarify this further, even though the data is available at 4:40pm, due to caching you may not see the new forecast until 5pm.

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Robert25 commented Friday, 14 Feb 2014 at 12:21pm

Ben, do you know why the 00Z run the most reliable?

thermalben's picture
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thermalben commented Friday, 14 Feb 2014 at 12:38pm

Because it contains the most obs/sonde data (12Z is also very reliable, however 06Z and 18Z and less reliable due to a smaller number of verification obs).

If you ever see wacky things in the model output, more times often than not (in my experience) it'll happen during the 06Z and 18Z runs.