Forecaster Blog: Strengthening Tradewinds over the Southwest Pacific Sees New E Swell Inbound Next Week

5 Feb 2019 1 Share

Ben Macartney

Chief Surf Forecaster

Issued Tuesday, February 5, 2019

The development of the monsoon trough was a long-time coming this year. Its activation over the far north culminated in an unprecedented deluge for Townsville this week, and as of Tuesday, two deaths have been recorded and the city remains partially submerged by floodwaters. More broadly, the onset of the monsoon is linked to a Madden-Julian Oscillation pulse moving through Australian longitudes. Over the coming week, this pulse will gradually migrate eastward over the Southwest Pacific; triggering a deepening of the monsoon trough over New Caledonia and Fiji.

In line with the MJO’s eastward propagation, the key models have been gradually zeroing in on a tropical depression (TD06F) forecast to deepen directly over Fiji over the next few days. By Friday we should start to see the TD06F commencing a poleward track – and as this occurs it will trigger a gradual strengthening of easterly tradewinds to its south. This occurs in conjunction with a large high-pressure system moving east of New Zealand on Thursday and Friday; supporting a broad subtropical ridge across the Southwest Pacific Ocean.

This recent IR Satellite image depicts the flaring convective signature over northern Queensland on Tuesday. It will be closely followed by enhanced activity over Fiji over the coming week. Source: Met Fiji.

This recent IR Satellite image depicts the flaring convective signature over northern Queensland on Tuesday. It will be closely followed by enhanced activity over Fiji over the coming week. Source: Met Fiji.

The Good News And The Bad News
So, on the upside, this presents much better than average chances for a mid-period easterly groundswell arriving along the entire Eastern Seaboard over the course of next week; manifesting as a notable upswing in both wave height and period from Monday or Tuesday onwards.

Latest model runs are displacing the developing low and fetch-area to the southeast; thereby downgrading E swell potential for the East Coast. This may well shift back in our favour as the system develops later this week. Source: Wave Tracker.

Latest model runs are displacing the developing low and fetch-area to the southeast; thereby downgrading E swell potential for the East Coast. This may well shift back in our favour as the system develops later this week. Source: Wave Tracker.

The bad news is an incremental downgrading in swell-potential that’s been showing up on consecutive model runs over the past couple of days. This is linked to several factors; including a slightly quicker eastward movement of the sub-tropical high east of NZ, pulling the head of swell-producing fetch further out towards the dateline. Recent model runs are also downplaying the intensity and longevity of the tropical storm as it moves south and transitions to a sub-tropical low. All this is further compounded by a more rapid south-eastward contraction of the fetch area, pulling it substantially inside the North Island’s swell shadow by Monday morning.

This image depicts peak wave period for SE QLD forecast for next Monday afternoon. However it pans out, an upswing in both wave height and period looks likely, particularly for southern Queensland and northern NSW early next week. Source: Wave Tracker.

This image depicts peak wave period for SE QLD forecast for next Monday afternoon. However it pans out, an upswing in both wave height and period looks likely, particularly for southern Queensland and northern NSW early next week. Source: Wave Tracker.

Having said all that, there’s still every chance the models will shift back in our favour as the system begins to develop over the next few days. However it plays out, we can definitely look forward to an extended run of Easterly swell across the Eastern Seaboard over the course of next week as the current run of short-period energy transition to longer-range, mid-period E swell originating north of NZ.

An increase in mid-period E swell looks like filling in across Sydney and locations south on Tuesday and Wednesday. Source: Wave Tracker.

An increase in mid-period E swell looks like filling in across Sydney and locations south on Tuesday and Wednesday. Source: Wave Tracker.

For more details on how this will play out, click here for the Southern Queensland and northern NSW forecast and here for the Sydney to South Coast forecast.

Beyond that, there are further, albeit speculative indications we’ll see a deepening monsoon trough spawning a couple of tropical lows over the Coral Sea next week – and there’s a distinct possibility that one or more of these lows will come into play leading into the middle of the month. Stay tuned for more clarity on these sources as the week progresses.

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

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