Forecaster Blog: Hello Tropical Cyclone Hola

8 Mar 2018 6 Share

Ben Macartney

Chief Surf Forecaster

Issued Thursday, March 8, 2018

As I write, severe, category 4 Tropical Cyclone Hola is continuing to intensify just northwest of New Caledonia; generating sustained winds of 110 knots around its core. For now both the storm and its phenomenal core wind-field remain firmly out of range of the Eastern Seaboard; owing to its swell-inhibiting location, directly inside New Caledonia’s swell shadow. Hence in the short term TC Hola remains an indirect producer of ESE tradewind swell as it interacts with a broad subtropical ridge to the southwest.

Could this be a glimpse into TC Hola's forecast swell potential for this time next week? Time will tell. Photo: Ethan Cole.

Could this be a glimpse into TC Hola's forecast swell potential for this time next week? Time will tell. Photo: Ethan Cole.

The good news is we’ll see TC Hola turning south and moving directly into our easterly swell window this weekend – and once this happens we could see the development of solid round of ESE groundswell getting underway; speculatively culminating in great conditions across the entire Eastern Seaboard mid next week. Now for the ‘but’ part. First of all, if you’re contemplating a repeat of the TC Gita swell, think again. For now the prospect of any major easterly groundswell looks tenuous – and like many a tropical cyclone, this event could amount to more of a hoax rather than something for the history books.

The latest MSLP chart shows TC Hola tucked away inside New Calendonia's swell shadow. That's all set to change as the storm accelerates poleward this weekend. Source: BOM.

The latest MSLP chart shows TC Hola tucked away inside New Calendonia's swell shadow. That's all set to change as the storm accelerates poleward this weekend. Source: BOM.

Regardless of what virtual buoy readings suggest, it’s always worth taking a step back from raw wave-data to look at the storm’s forecast behaviour. In this case, TC Hola is widely projected to accelerate away to the SSE over the weekend before slamming directly into New Zealand’s northwest coast on Monday 12th March.

TC Hola is widely projected to accelerate SSE this weekend before slamming into NZ's North Islandn on Sunday or Monday. Source: JTWC.

TC Hola is widely projected to accelerate SSE this weekend before slamming into NZ's North Islandn on Sunday or Monday. Source: JTWC.

The key time-frame relevant to swell potential occurs as TC Hola moves poleward over the weekend; setting up a an expanding ESE in conjunction with the ridge to the south. However, compared to TC Gita’s westward movement, this will progressively draw the swell-generating winds away from the coast as it goes. Further, the duration of the fetch area is likely to be heavily constrained by TC Hola’s poleward acceleration; thereby further limiting its capacity to generate swell.

What looks impressive on latest Wave Tracker runs may prove a bit of a fizzer given TC Hola's rapid southward track. Then again, there's plenty of upside associated with an adjacent high pressure ridge building in from the southwest. Source: Wave Tracker.

What looks impressive on latest Wave Tracker runs may prove a bit of a fizzer given TC Hola's rapid southward track. Then again, there's plenty of upside associated with an adjacent high pressure ridge building in from the southwest. Source: Wave Tracker.

Now for the upside. The simultaneous development of a large high pressure system over the southern Tasman Sea provides excellent support for TC Hola. Indeed this offers high confidence for rapid expansion of the ESE fetch currently in place off southern Queensland; elongating eastward as well as broadening southward as TC Hola moves clear of New Caledonia.

Latest ACCESS model runs depict the expansive ESE fetch developing as TC Hola tracks south this weekend. Source: BOM.

Latest ACCESS model runs depict the expansive ESE fetch developing as TC Hola tracks south this weekend. Source: BOM.

The key to this event may well come down to fetch-duration. Since it’s inception on Monday, we’ve seen persistent divergence between the key GFS and ECMWF computer models muddying the forecast waters. Based on the former, TC Hola’s swell generating potential will come to an abrupt end as it moves over the North Island on Sunday and Monday; and based on this we’re more likely to see a mid-sized round of ESE groundswell filling in across the region at 3 to 5ft levels on Tuesday and Wednesday. 

This Wave Tracker frame depicts peak wave period; showing a strong pulse of ESE groundswell will arrive in the vicinity of 3 to 5ft on Tuesday. This could evolve into something bigger arriving a day or two later. Source: Wave Tracker.

This Wave Tracker frame depicts peak wave period; showing a strong pulse of ESE groundswell will arrive in the vicinity of 3 to 5ft on Tuesday. This could evolve into something bigger arriving a day or two later. Source: Wave Tracker.

In contrast, EC runs pick up a more gradual SSE track that would extend the duration of the easterly fetch area out by (roughly) an additional 24 hours. This could significantly compound the size of the resulting ESE groundswell – and this possibility is keeping the door open to a larger swell event peaking in the 4 to 6ft plus range on Wednesday/ Thursday.

The forecast for this time frame is now being further compounded by the prospective development of a new tropical low/ cyclone within closer range of the Queensland coast early next week. For now there’s even less certainty on how this will play out, so stay tuned for updates on both systems in Friday’s detailed forecast.

The groundswell would arrive across the NSW coast almost simultaneously, albeit at a somewhat smaller size on Tuesday. Stay tuned for more in Friday's detailed update.

The groundswell would arrive across the NSW coast almost simultaneously, albeit at a somewhat smaller size on Tuesday. Stay tuned for more in Friday's detailed update.


Tags: Forecaster Blog , Tropical Cyclone Hola , Ben Macartney , Quiksilver Pro (create Alert from these tags)

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