Forecaster Blog: Tropical Cyclone Marcus

20 Mar 2018 5

Ben Macartney

Chief Surf Forecaster

Issued Tuesday, March 20, 2018

It’s always a long time between drinks when it comes to cyclone swells along the West Coast, but there’s now growing confidence a fleeting window of opportunity to score one of these rare swell-events will present itself across the Southwest this weekend.  This all hinges on the forecast behaviour of Category 4 Tropical Cyclone Marcus. The severe cyclone is currently tracking westward, into deeper water off the Pilbara coast and it’s projected to further intensify as it maintains a westward track over the next 24 hours or so.

TC Bianca produced this one-day-wonder that will go down in the history books across the Southwest. Photo: Dan Wyer.

TC Bianca produced this one-day-wonder that will go down in the history books across the Southwest. Photo: Dan Wyer.

From Thursday onwards TC Marcus is projected to curve south – and it’s at this point the cyclone will enter the critical phase for determining the specific surrounding arrival times and the peak-size of the north-swell arriving across the Southwest this weekend. The absence of any length of breadth to the northerly winds wrapping around TC Marcus’s upper eastern flank means we’re entirely reliant on the storm’s SSE track dragging the strongest area of core, clockwise winds within close range of the coast later this week.

FOLLOW TC MARCUS'S DEVELOPMENT ON THE WAVE TRACKER

Cat 4 TC Marcus will continue to move west over the next day or so before curing poleward on Thursday. Source: BOM.

Cat 4 TC Marcus will continue to move west over the next day or so before curing poleward on Thursday. Source: BOM.

There's now high confidence TC Marcus' turn to the south will bring the storm within close range of the Margaret River region by Friday, leading in a rare NNW swell for the region this weekend. Source: JTWC.

There's now high confidence TC Marcus' turn to the south will bring the storm within close range of the Margaret River region by Friday, leading in a rare NNW swell for the region this weekend. Source: JTWC.

As discussed in Dan Wyer’s latest forecast, the models appear to be falling into step regarding TC Marcus’ poleward track – and this is now definitively pointing to a powerful, albeit short-lived pulse of directional NNW groundswell filling in across the Southwest over the weekend.  The acute directional band associated with this event is likely to translate into widely varying surf-heights and it also looks like strong SE winds could make for tricky conditions as the leading edge of the swell fills in. Click here for a detailed rundown on how this event looks like unfolding.

It's not every day you see a purple blog moving south off the Western Australian Coast, but that's exactly what's forecast to occur as TC Marcus moves south later this week. Source: Wave Tracker.

It's not every day you see a purple blog moving south off the Western Australian Coast, but that's exactly what's forecast to occur as TC Marcus moves south later this week. Source: Wave Tracker.

If you’re wondering just how rare these events can be, then read on. It’s been just over six years since the last pulse of NW swell, generated by Tropical Cyclone Iggy, briefly lit up the region back in February 2012. 

Tropical Cyclone Iggy had all sorts of weird and wonderful wave effects across the Southwest back in 2013. So too could TC Marcus this weekend. Photo: Dan Wyer.

Tropical Cyclone Iggy had all sorts of weird and wonderful wave effects across the Southwest back in 2013. So too could TC Marcus this weekend. Photo: Dan Wyer.

As Dan Wyer wrote in the wake of the TC Bianca swell: “By dawn on Thursday the swell had ramped up to a peaky two-to-three feet, and exposed breaks around Cape Naturaliste were also seeing sets from the south making for some solid wedging peaks in the three-to-four foot range. 

Further up the coast, north facing breaks around Yallingup were copping the full brunt of the swell. By midday there were some surprisingly solid six-foot sets pushing through at Yallingup main break. The north swell produced some epic line-ups as usually placid waves turned into grinding Indo-style barrels and straight-hander beach-breaks became winding, East Coast-style point breaks. Winds stayed offshore from the southeast all day, keeping conditions clean". 

In 2013 TC Iggy crossed the West Coast well north of the Southwest between Geraldton and Jurien Bay. Recent model runs suggest TC Marcus could do something similar. Source: BOM.

In 2013 TC Iggy crossed the West Coast well north of the Southwest between Geraldton and Jurien Bay. Recent model runs suggest TC Marcus could do something similar. Source: BOM.

However, it was almost exactly one year to the day prior to TC Iggy that a far more impressive NW cyclone swell turned usually straight-hand beach-breaks into grinding, 6 to 8ft right-hand perfection. This all went down in late January 2011 when Tropical Cyclone Bianca tracked south, parallel to the West Coast before turning east and tracking directly towards the Southwest on February 2nd

TC Bianca tracked further south than TC Iggy, undergoing extratropical transition and re-intensifying within close range of the Southwest in late January 2011. Source: BOM.

TC Bianca tracked further south than TC Iggy, undergoing extratropical transition and re-intensifying within close range of the Southwest in late January 2011. Source: BOM.

According to those who were lucky enough be on the spot, TC Bianca produced a powerful NW groundswell that came and went in the blink of an eye; jumping from knee high to 6 to 8ft plus and then back to near flat again all in the space of one day.

However, prior to TC Bianca and Iggy, you have to travel a lot further back in time to find a NW swell of TC origins. In fact, you have to go all the way back to April 1978, when Tropical Cyclone Alby accelerated SSE off the West Coast before hammering the Southwest Coast. Whether or not TC Alby supplied the Southwest with an epic day of NW swell is lost in the mists of time, but the five deaths, extensive flooding and wind-damage caused by ex TC Alby as it moved within close range of Cape Leeuwin are well documented.

TC Alby's poleward track and extratropical transition near the Southwest wrought havoc on the region, killing five people and leaving a trail of destruction in its wake. As for the surf it generated? Lot in the mists of time is seems. Source: BOM.

TC Alby's poleward track and extratropical transition near the Southwest wrought havoc on the region, killing five people and leaving a trail of destruction in its wake. As for the surf it generated? Lot in the mists of time is seems. Source: BOM.

It's not hard to surmise that the onset of global warming over the last few decades is increasing the poleward reach of tropical cyclones. If that proves correct, perhaps these rare TC Induced north-swell events may not be quite so rare in the decades to come.

If TC Marcus behaves as current model guidance suggests, we'll see a strong pulse of NW groundswell materialising across the Southwest this weekend.

If TC Marcus behaves as current model guidance suggests, we'll see a strong pulse of NW groundswell materialising across the Southwest this weekend.


Tags: Forecaster Blog , Tropical Cyclone Marcus , Ben Macartney , Dan Wyer , Tropical Cyclone Iggy , Tropical Cyclone Bianca , Tropical Cyclone Alby (create Alert from these tags)

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