Forecaster Blog: Dual Tropical Cyclones Lining up to Deliver Days of Pumping Easterly Groundswell to the East Coast.
We’re now entering the early stages of a highly active phase in wave-generating throughout our tropical swell-window: one that looks like sustaining a consistent and sizeable run of surf across the Eastern Seaboard over the next ten days or so.
An MJO pulse propagating eastward across the tropical Pacific Ocean is now bearing synoptic fruit, with two notable tropical cyclones now active along the monsoon trough spanning the northern Coral Sea and Southwest Pacific. To best get a handle on swell-potential we’ll take a look at these systems sequentially, starting with the more distant, category 3 Tropical Cyclone Ana, now located just south of Fiji.
Tropical Cyclone Ana: TC Ana (TD05F), commenced its lifecycle as a tropical depression located roughly halfway between Fiji and New Caledonia on Friday. The system steadily intensified as it tracked east on Saturday before moving directly across Fiji as a category 2 system on Sunday.
TC Ana reaches maximum swell-generating potential on Monday: Early Monday morning saw TC Ana moving about 200km south of Fiji and further intensifying to a category 3 cyclone. The storm is supporting a broad ESE fetch area in conjunction with a subtropical ridge to the south, mostly at speeds of 20-30 knots. (note Another small cyclone, now ex TC Bina, is expected to be absorbed into TC Ana as they track south-eastwards along the sub-tropical ridge on Monday).
While these speeds are far from exceptional, TC Ana is supporting an impressive fetch-area in conjunction with TC Lucas over the Coral Sea (more on this guy below) and the aforementioned subtropical ridge to the south. That’s producing an expansive fetch, extending east to west in excess of 1,400 nautical miles across the tropical Pacific Ocean.
TC Ana departs our swell window, stage left: TC Ana endures as an effective swell-producer over the next 24 hours, spawning a vast, 3.5 metre wave-field before its south-eastward track draws its swell-producing winds out of effective range of our swell window on Tuesday night or by Wednesday morning.
And that’s roughly then our second tropical cyclone starts to come into play. TC Lucas is primed to capitalise on the pre-existing easterly wave-field generated by TC Ana to set up a larger easterly groundswell, developing within closer range of the East Coast over the next few days.
Category 2 Tropical Cyclone Lucas is tracking eastward at about 15 nautical miles per hour and currently lies well northeast of the mainland and hence out of direct swell-producing range of the East Coast. All the major computer models have fallen into step with early EC runs: unanimously indicating TC Lucas will curve southeast on Tuesday night, on a trajectory taking it around the eastern periphery, or directly over New Caledonia as it weakens into a sub-tropical cyclone on Wednesday morning.
Either way, wave-growth accelerates as ex-TC Lucas moves poleward, with significant wave-height projected to ramp up to 20-25ft immediately south of New Caledonia on Wednesday. Further, ex TC Lucas’ is projected to as it retrograde (turn west to south-westward) back towards the Eastern Seaboard – and that’s highly conducive to continued wave-growth within incrementally closer range of the NSW coast into Friday and Saturday.
Two overlapping pulses straddle Friday/Saturday and Sunday/Monday: So, although current model runs favour a peak in energy across Sydney and surrounds on Saturday, there’s every chance we’ll see a second, even larger pulse overlapping to produce larger surf on Sunday and Monday - this will all become clearer over the next few days.
Southern Queensland and far northern NSW: These developments definitely point to a powerful round of easterly groundswell: the bulk of it aimed at southern Queensland and northern NSW on Friday. That presents loose potential for heavy, 6-10ft surf across the exposed coasts, wrapping at an energetic 4-8ft across the points and bays – but these estimates will be refined in light of TC Lucas’ behaviour over the next few days.
Sydney, Newcastle and the South Coast: A still sizeable groundswell should spread south at a more ENE angle across the southern half of the NSW coast this weekend; conservatively arriving in the 4-6ft+ range across the majority of exposed beaches, with larger peaks in the vicinity of 6-8ft likely during the peak of the swell.
The starts are aligning for Sunday: Finally, there are additional developments now lending weight to the possibility of light offshore west to WNW winds greeting the swell on Sunday. That’s linked to a cut-off low forecast to develop south of Tasmania this weekend, extending a westerly flow across the NSW coast, before eventually leading in a fresh southerly change across the region on Monday 8th February. Stay tuned for updates on this as the week progresses.
A distant Southwest Pacific cyclone holds latent east swell potential in the lead-up to Christmas.
A resurgent La Nina is about to rock the East Coast this December.
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