Forecaster Blog: Tropical Cyclone Fehi’s E swell Potential

29 Jan 2018 3 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | FORECASTER BLOG

Issued Monday, 29 January 2018

Following on from last week’s Forecaster Blog, the much anticipated development of a tropical low over the northern Coral Sea culminated in the naming of Tropical Cyclone Fehi (TC Fehi)by the Fiji Meteorological Service on Monday morning. But before you take to the streets dancing in celebration it’s worth digesting a few hard facts about the system and it’s swell potential – particular for the southern half of the NSW coast.

Over the course of last weekend the tropical low tracked away to the east-southeast and this eventually took it out of the BOM’s sphere of influence on Sunday night. The first thing to note is that, overall, surf-potential (both with respect to size, period and longevity) has been downgraded across the board.

This was TC Fehi at midday Monday. It has since been downgraded back to tropical low status and will continue to track south on Tuesday and Wednesday. Source: Fiji Meteorological Service.

This was TC Fehi at midday Monday. It has since been downgraded back to tropical low status and will continue to track south on Tuesday and Wednesday. Source: Fiji Meteorological Service.

Based on recent reports the category one system was located roughly 260 nautical miles northwest of Noumea, New Caledonia. The storm is located within a hostile environment with respect to further development, featuring high vertical wind-shear – and this looks like it will inhibit potential for further intensification as a tropical system. Indeed there’s some conjecture as to whether or not it will retain its structure under the high-shear environment – and if it does break down prior to extratropical transition we may be looking at further downgrades to E swell potential over the next 24 hours.

As ex TC Fehi continues to track south on Tuesday and Wednesday it will establish a stronger easterly fetch throughout our swell window, setting up a solid round of E groundswell for the entire region from Wednesday to Friday. Source: BOM.

As ex TC Fehi continues to track south on Tuesday and Wednesday it will establish a stronger easterly fetch throughout our swell window, setting up a solid round of E groundswell for the entire region from Wednesday to Friday. Source: BOM.

Southern Queensland and northern NSW
For southern Queensland, the news is still pretty good. Even as as I tap away right now it’s clear on the cameras that the swell has continued to pick up across the region throughout the day – and this is set to culminate in larger surf from Tuesday onwards, with peak size and period anticipated to hold throughout Wednesday and early Thursday, preceding a steady easing trend following throughout Friday and the weekend. As alluded to on Friday, it’s now clear the poleward acceleration of the system will take it swiftly southward through the eastern Tasman and across New Zealand on Wednesday and Thursday – and this will curtail the duration of the easterly fetch that’s now setting up inside our swell window.

The end result is a smaller than originally projected peak in the 4 to 6ft range, with a steeper decline in E following throughout Friday and the weekend likely to be offset by a steep rise in shorter period SSE swell. Strong SSE winds will lend the surf-focus to the points and bays for the duration of this event – and along with the southerly airstream will come a strong building trend in SSE swell that will provide some solid reinforcement to surf-heights later this week. For more detail on conditions check the detailed forecast here.

The bulk of mid-period E groundswell generated by TC Fehi fills in throughout Wednesday and Thursday, making for good to great conditions inside the points and sheltered bays.

The bulk of mid-period E groundswell generated by TC Fehi fills in throughout Wednesday and Thursday, making for good to great conditions inside the points and sheltered bays.

Sydney, Newcastle and the South Coast.
The new isn’t so great for the southern half of the NSW coast: not because of the swell – but because of the persistent onshore winds forecast to accompany it. We’re now looking at smaller than originally projected peak in the 4 to 6ft range across the more exposed beaches on Thursday, with a steeper decline in energy following throughout Friday and the weekend. To put a further dampener on things, strong onshore SSE winds will butcher the best of the groundswell on Thursday and they’ll probably continue to hamper conditions throughout Friday and the weekend.

The arrival of a cold front early on Wednesday leads in a gusty southerly airflow, supported by a strong ridge of high pressure building in from the southwest. A large, slow moving high over the Bight maintains the ridge for several days; supporting fresh onshore S to SSE winds across the coast throughout Thursday, before moderating as the high moves eastward on Friday and the weekend.

The southerly flow will inevitably limit good surfable options to the most sheltered southern corners and north facing breaks – and even these are unlikely to be epic under Thursday’s still fresh SSE breeze. At this stage it looks like Friday morning will offer up some better quality 3 to 4ft plus options at these venues as S winds drop to 10 to 15 knots, but this will become clearer as the week progresses. For more details check the Sydney to South Coast forecast here.

FOLLOW THE PROGRESS OF THE SWELL ON THE WAVE TRACKER

A tale of two swells: The Wave Tracker displays peak wave period; illustrating both E groundswell and shorter period S swell arriving simultaneously on Thursday to make for fairly chaotic conditions along exposed breaks all day.

A tale of two swells: The Wave Tracker displays peak wave period; illustrating both E groundswell and shorter period S swell arriving simultaneously on Thursday to make for fairly chaotic conditions along exposed breaks all day.


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

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