Forecaster Blog: Tropical Cyclone Victor Aims Days Of Long Range E Groundswell Our Way
FORECAST | Cyclone Watch
Issued Tuesday, January 19, 2016
- Category 3 Tropical Cyclone Victor, (TC Victor) located about 360 nautical miles west of Raratonga, is the source of a long-range easterly groundswell arriving across the entire Eastern Seaboard later this week.
- TC Victor supports a broad easterly fetch across its southern quadrant as it remains slow moving over the Southwest Pacific all week, aiming large seas and swell westward towards Australia’s East Coast.
- The vast distance between the swell source and the coast results in significant wave erosion prior to landfall and also exacerbates wave dispersion, meaning long waits between sets.
Back in the day, before the emergence of surf forecasting, swell-events flew under the radar on a regular basis. They were the days when having a direct line of sight to your local break from your bedroom window paid dividends, allowing one to be among the first to jump on such swells. Even these days we’re still occasionally taken by surprise by an unexpected pulse of swell, but by and large the abundance of swell-forecasting data and information at our fingertips ensures very little slips below the radar. That definitely applies to the latest source of swell for Australia’s Eastern Seaboard currently churning out fresh lines of easterly groundswell over a remote region of the Southwest Pacific – Tropical Cyclone Victor.
Track the live progress of this cyclone on the Coastalwatch Wave Tracker
Severe Tropical Cyclone Victor (TC Victor) is the third tropical cyclone to form over the South Pacific region this season – and its remote location and category 3 intensity are line with seasonal forecasts associated with the strong El Nino currently dominating the Pacific Ocean. The system commenced its lifecycle as a slow-moving tropical depression east of Samoa early last week. The tropical depression was located in an excellent environment for further development; characterised by a weak poleward steering mechanism, low vertical wind shear and high sea surface temps. Subsequently, the low was named as TC Victor by the Fiji Meteorological Service late on Friday 15 January. Since its inception TC Victor has drifted very slowly south at speeds of 5 to 10 knots and as of Tuesday morning the system was still on a southward trajectory, located approximately 365 nautical miles west of Raratonga – or more poignantly – roughly 2,245 nautical miles east of Australia’s east coast.
Over the last few days the system has maintained category 3 strength and wind speeds of 90 knots around its core and gale to storm force winds within a radius of 100 to 200 nautical miles of the eye – and there’s now high confidence we’ll see several days of small to mid-sized easterly groundswell arriving off this system later this week. Maximum significant wave height generated by TC Victor was up around 30ft on Tuesday and the system will continue to support this sea state as it continues on a slow poleward track over the next 24 hours. From there, TC Victor is projected to curve sharply west under the influence of a developing subtropical ridge building southwest of the system – and this is good news for surfers residing along Australia’s East Coast.
Although TC Victor has now reached peak intensity and is forecast to gradually weaken under increasing vertical wind-shear and decreasing SSTs over the coming days, it’s still projected to support a compact easterly fetch across its southern quadrant; gradually drawing the swell-producing winds within closer range of Australia’s East Coast as it curves west towards Tonga on Wednesday and Thursday.
The upshot is a long enduring easterly swell-train arriving across the East Coast from Thursday onwards. The leading edge of a first pulse is likely to be evident at 1 to 2ft levels early on Thursday ahead a slow build into the 2 to near 3ft range during the afternoon. Keep in mind there will be long waits between sets and across the NSW coast localised NE windswell initially persists as the primary source of surf on Thursday. However, by Friday morning a mid-sized easterly groundswell should be well and truly be evident across the entire East Coast, generating sets to 2 to 3ft plus ahead of a further push in size as the day progresses.
The early season formation of Tropical Cyclone Tuni provides a kind of analogue case by which to gauge swell potential associated with TC Victor. Although TC Tuni’s lifecycle played out over the exact same Southwest Pacific region back in early December 2015, its characteristics were entirely different from TC Victor. TC Tuni only briefly reached category one strength before being downgraded to a tropical low and it’s south-eastward track was hardly conducive to major wave-growth.
The one thing TC Tuni had over TC Victor was a much larger and stronger area of high pressure supporting it from the south. Where the E swell event associated with TC Tuni was primarily high pressure driven, the impending TC Victor swell originates more directly from the cyclone itself. TC Victor is supported by a smaller and weaker high-pressure system and hence the associated wind-fetch encompasses a smaller surface area than it’s TC Tuni counterpart. However, TC Victor has maintained category 3 strength for an extended duration and its westward movement will further enhance associated swell potential over the next few days.
So, all this begs the question: Which system exhibits better swell producing characteristics: TC Tuni or TC Victor? Going on the numbers crunched out by WW3, deepwater wave-height produced by both storm-systems are roughly on par. The real differentiator is peak wave period. Where the swell generated by TC Tuni reached peaks of 12 to 13 seconds, TC Victor is forecast to sustain higher peaks ranging from 13 to 16 seconds - over a longer time frame to boot. Given higher peak-wave periods carry deepwater wave-energy with greater efficiency, it’s fair to conclude the impending E groundswell arising from TC Victor will exceed expectations – but only time will tell.
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