Bass Strait swell conditions

Posted by: thermalben

Bass Strait swell conditions - 07/08/2003 10:17

As mentioned in the 'surf conditions..' thread, we are experiencing an impressive swell event along the southern coastline at the moment. However, I'm not sure where the BOM are deriving their Bass Strait forecasts from - there's around 6m sig of WSW swell pushing through the region, with a peak wave height of 14.5m (48') eek recorded at midnight on the Cape Sorell waverider buoy.

However, the official forecasts issued are as such:

Thursday until midnight : West/northwesterly winds 15/20knots, locally 25knots. Seas 1 to 2 metres, 3 metres offshore. West to southwesterly swell around 3 metres.

Thursday until midnight : North/northwesterly winds 15/20knots tending more westerly offshore and locally 25 knots. Seas mainly 1 to 2 metres. West to southwesterly swell 2 to 3 metres.

Thursday until midnight : West/northwesterly winds 10/15 knots inshore, 15/25 knots offshore. Seas around 2 metres. West to southwest swell 1 to 2 metres.

Thursday until midnight : West/northwesterly winds 25/35 knots, easing to 15/25 knots during the day. Seas chiefly 3 to 4 metres, abating to 2 to 3 metres during the day. Westerly swell around 3 metres, reaching 4 to 5 metres about the far west.

A 3m swell forecast is quite routine for this part of the world in winter, however we are experiencing one of the largest swell events of the year and I think that this is a huge undercall on part of the BOM. I'm not sure what kind of impact this would have on boating/fishing operaters in the region (fancy a trip over to Tasmania on the ferry under these circumstances?), but with this swell event expected to persist right into the weekend I am a little concerned that it not being accurately assessed.

Thoughts anyone?
Posted by: pingtang

Re: Bass Strait swell conditions - 17/08/2003 23:16

Hello Thermalben.

I also think '2-3metres' was a significant undercall.As you said,that sort of a swell is quite common in southern waters.How big did it end up getting?

Even the east coast of NSW got a decent swell,which was definatly more than 2-3metres.On the peak of the swell,I definatly saw some open ocean swells approaching 4-5metres.

This isnt the first time,the coastal waters forcast seriously undercalled a swell.I can even give you an example from today.The coastal waters forcast said "swell near 1metre".That should pretty much mean flat,yet I caught a wave which would have approached double overhead.Heres another example-a few years back(July 6 2001 to be precise)a deep low pressure was sitting on the top of New Zeland.A high was sitting under it,generating a tight pressure gradient.Strong easterly winds blew over a long stretch of water generating a large swell.The coastal waters forcast for that day said "swell near 1 metre",however it was much larger than that.It was actually 5metres,and that was with offshore winds.Sometimes these forcasts are so off the mark its not funny.
Posted by: thermalben

Re: Bass Strait swell conditions - 18/08/2003 00:51

Hi Pingtang

Great to see someone else besides me has an interest in this topic! smile

The surf for this particular event ended up being really big - 8' at Bells with occasional 10-12' rogue sets. The exposed East Coast beaches (Gunnamatta, Portsea etc) peaked in the 12'+ range - certainly one of this biggest events over the last year or so. SA was huge aswell.

Anyway, just for comparison, I have checked the Bass Strait forecast for tonight and tomorrow, and it reads:

Monday until midnight : Seas to 2 to 4 metres easing to around 1 metre by the end of the day. West/southwest swell 3 to 4 metres decreasing to near 2 metres later.

Monday until midnight : Seas 2 to 3 metres decreasing to 1 metre by the evening. West/southwesterly swell 2 to 3 metres decreasing to 1 to 2 metres.

Monday until midnight : Seas 2 to 3 metres. West to southwesterly swell increasing to 1.5 to 2 metres.

Monday until midnight : Seas 2 to 3 metres
offshore and about the west. Westerly swell to 2 metres, tending southwesterly 3 to 4 metres about the far west.

The surf at Bells today was in the 2-3' range, with the East Coast beaches around 4-5'. This is less than 1/3 the height of the big swell mentioned above, yet the swell forecast is for 2-3m in Northern Bass Strait and 3-4m in Western Bass Strait tonight (ie the same as the aforementioned swell for Nth BS, and even larger for W'ern BS). My forecast for the Bells region for tomorrow (done on Thursday) was for an increasing swell to 3-5', but nowhere near the heights of the huge swell documented above.

Just on a side note, I'll be starting to forecast nationally in a week or two, with a web page upgrade too. With luck I'll be able to deliver a 5-8 day forecast 3 times a week (just have to fit it around uni wink )
Posted by: thermalben

Re: Bass Strait swell conditions - 01/12/2003 13:28

Bass Strait conditions appear to be under-called by the BOM for the impending swell pushing through the region. Cape Sorell is currently reporting 5m significant wave heights, with maximum wave heights up to 9m (@ 10s/15s) and are likely to increase further during the day. Pt Nepean is just starting to feel this new swell with significant wave heights of 2m and maximum just under 4m (this will increase further during the late arvo).

Issued at 1210 on Monday the 1st of December
Monday until midnight : Southeast to southerly wind at 15/20 knots, tending
east to southeasterly at similar strength later tonight. Seas of 1 to 2 metres.
Southwest swell rising 2 to 3 metres.
Tuesday : East to southeast wind 15/20 knots tending east to northeasterly in
the early morning and easing 10/15 knots in the north. Wind tending
southeasterly at 10/15 knots in the afternoon. Seas 1 to 2 metres. Southwest
swell 2 to 3 metres.

Monday until midnight : South to southwest wind 15/20 knots tending south to
southeasterly this afternoon at similar strength then east to southeasterly
tonight. Seas 1 to 2 metres. Southwest swell of 1 to 2 metres. Southeast swell
to 1 metre developing.
Tuesday : East/southeast winds 15/20 knots tending east to northeasterly by
morning and reaching 25 knots at times. Afternoon inshore seabreezes of 15/20
knots. Seas 1 to 2 metres rising 2 to 3 metres. Southwest swell 1 to 1.5 metres.
Southeast swell to 1 metre.

Monday until midnight : Southwesterly winds 10 to 20 knots, reaching 25
knots in the far west. Inshore afternoon sea breezes. Winds tending east to
northeasterly tonight at 10 to 20 knots. Seas 1 to 2 metres. Southwest swell to
2 metres in the west rising to 3 to 4 metres this afternoon. Northeast swell
elsewhere to 1 metre increasing 1 to 2 metres in the east.
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 01/12/2003 18:08

G'day Ben, I've been a bit slack on the forums, but I do check the marine one from time to time. 1-2m for northern Bass Strait is a little on the low side.
Surfwise tomorrow should be pretty good at Right Point and Woolamai. The wind might end up being a bit suss on the Peninsula though (might stay fairly east), Gunna might be okay - banks depending.
I've got my own surf forecast up on the web at the moment if you want to check it out....
Sky News are also displaying them each afternoon too as part of a mastercard promotion. Any feedback is welcome.
Posted by: thermalben

Re: Bass Strait swell conditions - 01/12/2003 18:52

Hi Alex

Nice to hear from you. I've known about your forecasts for a while - I stumbled across them some months ago.

I'm going for a slightly, erm, 'larger' wave height tomorrow though in Victoria - in all honesty I reckon it's going to be massive in the morning when the swell peaks. The Sorell buoy is still climbing - last reading was 5m Hsig, 9m Hmax @ 17 seconds, and looking at the storm's characteristics, I reckon that we'll see a few huge bommie sets tomorrow upwards of 8' on open beaches - possibly even 10'+ on the tide (wind speeds were around 70kts at the low's core). General residual swell should be in the 6-8' range though, and I can't see much surfing happening at Gunnamatta tomorrow despite the good winds. Not sure about Right Point either - I suppose it'll depend on the wind, but I was under the impression that ENE would be ribbing up the face at Right Point? Should be OK there in the arvo with the seabreeze. Maybe Flynns too with the ENE wind (as the wind pushes down the line rather than into the face), but not having surfed those locations I'll have to check it out soon.. possibly this Sunday actually smile Perfect size for that part of the world though! If the wind's good, Cat Bay will be ON!

The Pt Nepean buoy is also continuing to climb, but I'll be monitoring it closely tonight. We're currently putting in new cams in Victoria, and looking at Portsea this afternoon it's gotta be at least 6-8' (it was only 2-4' this morning). We're also installing a new one at Jan Juc right now (a robotic Sony, just like the new one at Snapper) - hopefully it'll be online by dusk so I can see how much it's picked up.

Still, as always.. have to wait and see!

Cheers, Ben

PS. BOM only going for 1.5m tomorrow.. amazing.. do they ever get any feedback? I hope no-one's planning a fishing trip based on this kind of info.
Posted by: thermalben

Re: Bass Strait swell conditions - 01/12/2003 18:54

ahh.. just checked the link.. you've upped the size slightly from this morning when I checked it wink
Posted by: thermalben

Re: Bass Strait swell conditions - 01/12/2003 19:18

just got a call from Bells - the surf's been building quickly all day, and is now around 6'+. Portsea looks enormous on the cams - gee.. what I'd do for a surf report update today from someone down there...
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 08:12

Had a report at 7am from this morning from a mate on the Peninsula. He checked Koonya (next to Sorrento) and called it 6ft. His 6ft is probably a solid 8ft to most though!
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 08:14

Just checked, it does look about 6ft from the stills(at Portsea). The Peninsula Surf Centre guys tend to call it a bit bigger than it is in my book wink
Bells report says 3-5ft.
Posted by: thermalben

Re: Bass Strait swell conditions - 02/12/2003 09:14

from's Woolamai report:
We had a large swell arrival yesterday which has now peaked( about 10'). Today the swell will taper off ,but at this stage there are still 8' bombs
Swell picked up yesterday and this morning is an uneven 8ft on the sets with a ENE wind
check the pics from Flynns last night too - just about epic!!

Looks like it peaked overnight - although the Pt Nepean buoy hasn't really deviated much from the peak just yet.. period is still holding in there around 12.5/15 secs (Tz/Tp). I ummed and ahhed so much yesterday before uploading my forecast - the peak was only even going to last a short period of time, but I wasn't sure whether those 10'ers would still be hanging around at dawn (in hindsight, it looks like they were a part of the leading edge of the swell - slightly unusual, but attributed to the origin of the swell I reckon). Pretty happy with my call though smile these events aren't always knocking at our doorstep like in other parts of the world.

Interesting about the size issue though - I've always been under the impression that the Portsea and Woolamai calls are slightly 'under' my expectations! I've spoken to the Woolamai reporter, who's agreed with me - he's normally a foot or so under what most people would call it. But there's a few other reporters that I know would be calling 3-5' Woolamai today - just like they're in Hawaii... :rolleyes:

However I actually forecast for the reporters, so to speak - makes it easier to verify with the actual trends. Although they're not always right either - take Sunday for example on the East Coast. Slowly dropping swell trend... Portsea and Woolamai both reporting 1-3' and 2-4' surf respectively.. then the Rye report comes back in and says that it's on the way up with consistent 4-5' sets!! I know for a fact that it wasn't.. maybe he saw 1 freak wave and didn't wait around too long. Just shows what a mug's game this forecasting business is wink
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 09:47

Hey Ben,
My initial 3-5ft a couple of days out was definitely an under estimation. The reason I went on the smaller side was due to the fact that the low was only intensifying at the last minute (so to speak) as it passed south of SA. I didn't think it really had the time to produce a 'monster swell'. With my forecasts I do have the constraint of doing a forecast for the whole of VIC so a I usual stick my swell size somewhere in between the east and west coasts(rather that writing 2-6ft, 4-8ft,etc!). Swell size is a tricky one and I take your point on forecasting for the reoprters and I usually do the same. I may have a little bias towards the small size however. But anyway, better get back to work. Good work on the forecast, you take the points on this one!
PS Wish I was in VIC today, the only option I have today is 6sec period wind swell in sydney frown
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 09:53

On the topic of reporters, I have no doubt when a big swell arrives the Portsea/Rye report is usually over estimated. On a few occasions when I have rushed down form Melbourne for a "10-12ft" swell, my beloved big wave spot was no where near breaking and it was more like 6-8ft. So I'm usually a little cautious on those reports and take a foot or two off.
Posted by: thermalben

Re: Bass Strait swell conditions - 02/12/2003 11:59

yes, the whole reporter issue is an interesting one. I'm delving into this slightly in my honours project too.. but it's kind of like letting a cat amongst the pidgeons - I doubt whether it'll uncover anything acceptable to the surfing community as a whole.

Just an interesting feature from Phillip Island's reports from yesterday - these images was called in at 'head high' (I've cropped them from

For my books, a head high wave is around 3' or so. But I'd call both of these pics in the 4' category - maybe even a little bigger on the second shot (hard to tell as the surfer is crouching, but it's certainly well overhead - maybe a foot or so), so I'd be inclined to call the first shot 4' and the second one 4-5'. Face size would be much bigger - the first one looks like it has a 6-7' face, while the second is around 7-9' feet (again, hard to tell).

But the reporter who called this head high (slightly under-calling in my opinion) also called Woolamai around 10' for last night too.

However the lines seem to blur above 8' for most reporters - it's certainly not easy distinguishing small increments in surf size when you're about to get clobbered by a triple overhead wall-of-death wink hehe
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 12:28

I'd agree 100% with your swell height comments. 4ft first photo then 4ft maybe 5ft in the bottom one. When it comes to overhead, double overhead and all that jargon it does mean much to me being a booooooooooogie boarder!
Posted by: thermalben

Re: Bass Strait swell conditions - 02/12/2003 12:39

hehe.. how about 'lid high', 'double lid', 'triple overlid'... just kidding wink

It's worse in Hawaii though - take last week's huge NE swell. Surfline were calling 20'+, Pat Caldwell (highly respected forecaster, works with NOAA) was calling 25-30' with bigger sets near 35'.

10' of difference in size estimation is pretty large - however I imagine it would have been 35-40' in Portsea terms! laugh
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 02/12/2003 13:33

If its the same Pat Caldwell, he was a former pro bodyboarder in the 80's who invented the 'El Rollo'!
Posted by: pingtang

Re: Bass Strait swell conditions - 02/12/2003 16:18

Hello Ben and Alex.

Interesting discussion you have going here.Ive read your posts from the last few days,and I couldent resist adding a few of my own.

The issue on size,can often be quite complicated.Obviously people have they're own opinions.Some overcall the surf,while others undercall the surf.The difference can be quite drastic in some cases.Looking at the photos,I would call the first wave a solid 3.5-4ft,while the second wave could be giving 4.5-5ft a nudge.I know some people who would call that wave 6-8ft,while others may call it 3ft.Heres an example of a serious undercall.Last winter,I headed down to Bawley point in the hope for some huge waves.Unfortunatly it was only double overhead-too small for the point to do its thing.I didnt bother going out,instead I went to some other break in Ulladulla.Before,I left I had a fairly long convesation with a surfer.Believe it or not,he called it 2-3ft on the sets.No Way!,it was definatly a solid 4-6ft.

How big,has Victoria been over the last 24hrs Ben.Im imagining the East Coast would have scooped 8ft++ sets.Also,is there a chance of some of that groundswell refracting up the NSW south coast tomorrow.I think you're forcast mentioned 2-4ft at fullon south facing beaches.Does that still look likely?.The winds will go northerly tomorrow,so there could be some fun ones at those exposed areas.If theres no south swell tomorrow,I'll have to look onto Saturday for abit of size.Im thinking Saturday,will have 4-5ft sets with a southerly.Anyway,great work with your forcasts.They're extremely usful.Your site is one of the first I visit on a Monday,Wednesday and Friday evening.Keep up the top work! smile
Posted by: thermalben

Re: Bass Strait swell conditions - 02/12/2003 18:05

Hi Pingtang

Thanks for the nice words. There's definitely some southerly swell expected to push into the Tasman Sea over the next 12 hours, but it's got a long way to go before it refracts into the coastline. Batemans Bay is the only buoy that picked up any new energy on the last update, but it'll need a couple more hours until I'm convinced that it's truly on the way in. Unfortunately, the next update isn't until 3am, so we'll have to sit tight through the night wink Still, I've seen increases to 3-4' on south-facing beaches (Wanda etc) this year from less vigorous airstreams - if the tide and currents are favourable, I reckon we should still see an increase early tomorrow, and I'm sticking to 2-4' (however this is extreme south-facing beaches only!! Manly et al will only see a continuation of this NE dribble). However those persistent northerlies really won't be adding much to the pot - but northern corners should offer both some protection as well as picking up the most swell energy. All in all, it's probably looking like the best day of the week in NSW.

By all reports in Vicco, the swell peaked up to 10' on open beaches late Monday and overnight (the Pt Nepean buoy also confirms this). There's more swell expected over the next week - a series of fluctuations from the SW, but nothing to the magnitide we saw yesterday.

I'm in the office now assessing things for the weekend's NNSW low - it'll be most interesting to see whether it develops, and to what magnitude. I wouldn't mind checking out some SST stats off the northern coast too - it's been a bit of a hot spot overthe last few weeks for cyclogenesis smile Saturday's now looking a little more promising now for southern NSW too - looks like Friday's change will pack a little more punch that hinted at in yesterday's model runs.

Cheers, Ben
Posted by: thermalben

Re: Bass Strait swell conditions - 26/11/2004 06:59

[Although this is dragging up an old thread, I thought it'd be worth comparing to previous notes on similar forecasts].

Just curious on the BOM's forecast for Bass Strait on Saturday - not so much the wind strength as the swell size. In the past, I have found that the BOM typically undercalls size quite significantly in Bass Strait (the swell event on Nov 16 that delivered solid 10' surf to Portsea was forecast 12 hours prior as "Seas around 1 metre.
West to southwesterly swell 2 to 3 metres", yet the Pt Nepean buoy held out around 3.5m Hsig / 6m Hmax @ 17secs for around 12 hours).

However, their current forecast for tomorrow is:
Saturday: North/northwesterly winds strengthening to 15/25 knots ahead of a
southwesterly change at 20/30 knots during the afternoon. Waves rising 2 to 3
metres. Southwest swell increasing to 2 metres
There is not a huge amount of difference between today's "2m" swell forecast and Nov 16th's "2-3m" forecast, except the Nov 16 swell event saw wave heights at Cape Sorell around 6.5m (Hsig) and 13m (Hmax) around the time that the forecast was issued. Current data at Cape Sorell is around 2m (Hsig) and 4m (Hmax), and Pt Nepean is around 1m/1.5m.

Comparing this with expected energy in the surf zone is even harder, as I can't see any size at all this weekend - in fact, I would not be overly surprised if it is flat in may places. I suppose I'm trying to find out how useful these kinds of forecasts are, as a quick glance at the BOM's Nov 16 forecast and today's forecast wouldn't offer much insight as to such a large deviation in surface conditions.
Posted by: thermalben

Re: Bass Strait swell conditions - 28/11/2004 15:21

For the record, Saturday was barely 1-2' on the East Coast's open beaches (and flat elsewhere), and it was even smaller this morning.

The Cape Sorell buoy eased from 1m Hsig (midnight Fri) to 0.5m (midnight Sat), so I have no idea where the BOM's 2-3m waves and 2m swell forecast came from - I'm pretty sure that their marine forecasts are primarily based on whatever the MLAPS WAM conjures up, but I had a quick glance on Friday after posting my previous comment, and it didn't suggest anything in this size range at all.
Posted by: Ripley

Re: Bass Strait swell conditions - 29/11/2004 17:49

Spent the weekend in the Warnambool area and the surf there was almost non-existant. Best wave we saw was at Beachport down the South East and a small shorebreak near Nelson on the SA-Vic border
Posted by: thermalben

Re: Bass Strait swell conditions - 13/12/2004 08:56

and again.. the BOM are calling for a 2m swell in northern Bass Strait tomorrow:
Seas 2 to 3 metres abating to around 2 metres later. Southwest swell near 2 metres
The surf will be unlikely to crack much more than 2-3' of short-period junky stuff on the East Coast's open beaches, and it is expected to remain small to flat in Torquay (perhaps some small windswell later).

Additionally, their forecast last Thursday night (for Friday) was:
East to southeast swell 1 to 2 metres
when in actual fact a long-range WSW swell (Tp over 18secs) delivered excellent 5-6'+ surf at Portsea and Gunnamatta during the day.
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 14/12/2004 21:26

Hey Ben,
Just on the Thursday night forecast by the BOM, although the bulk of the swell was from the W/SW there was definitely a detectable underlying SE swell when I surfed Portsea. Also, on the height I don't thing the were to far wrong. It was 3-4ft for the most part with only the very rare 5footer. And that is being generous. A mate told me surfshop were reporting 6ft at Portsea on Saturday which was laughable.
So I guess they weren't totally accurate, but it wasn't as bad as some of their others!! wink
PS Still waiting on photos of the big swell some weeks ago, I'll try and get my hands on them soon....
Posted by: thermalben

Re: Bass Strait swell conditions - 14/12/2004 22:17

hey Alex

Ahh.. fair 'nough - the surfshop morning report was 5-6' or so, and buoy data increased in strength during the day so I assumed it peaked just above this. Reports from the previous few days has also noted the SE swell - so I was aware of its presence - but I suppose I was pointing out that the BOM missed a long period SW swell completely (Tp of 18 seconds isn't an everyday occurence in December).

As for today, there is no groundswell whatsoever - Cape Sorell didn't move until around 3pm (of which is was all local swell), but a locally strong onshore flow has kicked up some windswell along the Vicco coast - Tp up to a whopping 7 seconds at Pt Nepean!!

Can't wait to see those photos too smile

Posted by: thermalben

Re: Bass Strait swell conditions - 03/01/2005 15:25

I'm really puzzled by this one for Northern Bass Strait:
Southwest swell to 1.5 metres, shifting easterly and rising to 3 metres
A 3m easterly swell? 3m is the 'upper end' of their forecast spectrum.. but only with SW swell events. I can't fathom how they came to this figure, as the SE/NE airstream is only expected to be up for 18-24 hours or so (not enough time to generate a 3m 'swell'.. and only at 15-25kts).

Additionally, the other regions are listed as such:
Western: "Southwest swell 1.5 to 2.5 metres. Easterly swell to 1 metre"
Eastern: "Seas 2 to 3 metres abating to 1 to 2 metres later. Southeast swell 1 to 2 metres"
Southern: "Seas 1 to 2 metres rising to 2 to 3 metres in the west. Westerly swell to 1.5 metres"
Posted by: Alex Zadnik

Re: Bass Strait swell conditions - 12/04/2005 16:15

Another undercall by the VRO.......

Northern Bass Strait:
Tuesday until midnight: Variable winds 5/10 knots tending east/northeasterly at 10/15 knots at night. Afternoon inshore seabreezes to 10 knots. Seas around 1 metre. West to southwest swell around 1 metre increasing to 1.5 to 2 metres in the west later.

Significant wave heights are up to 3m on the Point nepean wave buoy (which is not in the west of the above region). So the Bureau error here is pretty large.

Forecasts out of TAS were much closer to the mark.
SOUTHWEST COAST, South East Cape to Low Rocky Pt:
Tuesday until midnight: Westerly winds 15 to 25 knots, easing to 5 to 15 knots during the day then becoming variable. Seas 2 to 3 metres abating. Southwest swell 4 to 5 metres.

Cape Sorrel buoy is currently at 5m with max wave heights of 9m!
Posted by: Ripley

Re: Bass Strait swell conditions - 12/04/2005 21:11

By my reckoning we're in for great day of surf tomorrow down here in S.A. We had a half good wave today and as Benny said Wednesdays is going to be the pick of it. I'll still hold with my theory we're in for a great autumn and winter...mind you I feel it's going to be a cold winter this year with some of the biggest swells for quite awhile and I suggest you local Blokes/Sheila's have got the appropriate attire for the oncoming onslaught of great surf and cooler conditions...