Bali, Indonesia Surf Forecast 26 July - 5 August, 2017

25 Jul 2017 0 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | BALI, INDO SURF FORECAST 

Forecast Issued Tuesday, 25 July 2017

The wave-action keeps on coming at challenging levels across Indonesia as late July transitions to early August. The relentlessness of the Southern Ocean storm-track throughout the winter months effectively guarantees a succession of powerful groundswells; mostly characterised by smaller, mid-sized episodes in the 3 to 6ft range, but punctuated by several larger events peaking in the vicinity of 6 to 10ft plus.

SEE ALSO: These Are The 9 Best Boards To Take To Indo This Year

From little things, big things grow. An active Indian Ocean storm track continues to deliver a series of large groundswells to Indonesia throughout late July and early August. Photo: Bruno Veiga/ World Surfaris.

From little things, big things grow. An active Indian Ocean storm track continues to deliver a series of large groundswells to Indonesia throughout late July and early August. Photo: Bruno Veiga/ World Surfaris.

Short Forecast
A solid push in SSW groundswell sees larger 4 to 6ft conditions on Wednesday, briefly easing on Thursday ahead of a larger SSW episode building in throughout Friday and the weekend. This is reinforced by another, similarly large SSW pulse into Sunday and Monday, with another even larger SSW episode on the cards for the 3rd and 4th of August.


Daily Summary

Wednesday 26
New SSW groundswell. Sets around 4 - 6ft exposed breaks, grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending ESE 15 to 20 knots.

Thursday 27
Easing SW swell reinforced by rising long-interval SSW groundswell. Ranging from 3 - 5ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending light ESE around 17 to 22 knots.

Friday 28
SSW groundswell. Ranging from 5 – 8ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE around 10 to 12 knots.

Saturday 29
SSW groundswell continues. Sets to 5 – 8ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE around 10 to 20 knots.

Sunday 30
Reinforcing SSW groundswell peaking during the afternoon. Sets to 6 - 8ft+ exposed breaks, speculatively rising to 8 – 10ft. Grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending ESE 15 to 20 knots later.

Monday 31
Large SSW groundswell slowly eases. Sets to 8ft+ exposed breaks early, easing during the day. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE around 10 to 20 knots later.

Overview
There’s no shortage of Indian Ocean juice on tap into the final week of July – and it’s now looking like early August is going to kick off with a bang. The immediate outlook sees a new, robust  pulse of long-period SW groundswell inbound across The Archipelago; the leading edge of which was already starting to show across exposed breaks on Tuesday.

As the bulk of this swell fills in on Wednesday expect long, clean lines stacking up at 4 to 5ft plus across the most exposed breaks.  This marks the first of two long period episodes linked to an active storm-track that set up below South Africa and Madagascar over the course of last week. Wednesday’s first pulse was generated by a broad area of zonal (westerly) winds exhibiting speeds of 30 to 50 knots; supported by a broad, complex low pressure gyre situated below South Africa.

The vast distance between this source and Indonesia eroded a fair portion of the deepwater energy; so although leading forerunners of 18 to 20 seconds start to fill in throughout Tuesday, these are likely to go largely unnoticed until the bulk of swell arrives on Wednesday. The swell should continue to run at solid 3 to 5ft levels early on Thursday, with a slow decline underway as the day progresses.

However, it’s clear that Wednesday and Thursday’s initial upswing will be overshadowed by a second, larger episode that will overlap with the tail end of the first into Friday and Saturday. This linked to a much larger and stronger extratropical low that developed over the same storm-track, below South Africa and Madagascar mid to late last week.

This broadscale system established a vast area of gale to storm force WSW winds as it intensified below South Africa, with satellite passes confirming a broad area of 40 to 55kt wind speeds over the region last Thursday. This in turn generated maximum significant wave-heights in excess of 40ft over the Southern Ocean on Thursday and Friday. These impressive numbers, coupled with the larger scale of the storm should see a larger round of long-period SSW groundswell; showing up at solid 5 to 8ft levels on Friday and hanging in at similar levels throughout the weekend.

The deep low beneath South Africa subsequently filled over the last few days; breaking down into a still large, but relatively weak low pressure complex over the southern Indian Ocean. However, as this system migrates into Western Australian longitudes over the next few days it will gradually re-emerge as a significant mid latitude low positioned directly south of Indonesia. The storm is projected to set up several days of SSW to SW gales directly south of Bali and Java; in turn spawning another strong, reinforcing pulse of SSW groundswell inbound from 200 to 210 degrees on Sunday and Monday.

There are indications this will compound surf heights during Sunday as it overlaps with the tail end of the Friday and Saturday’s SW groundswell; pushing set waves up into the 8 to 10ft range across exposed breaks during the day. This episode should continue to run at similarly large levels on Monday, preceding a slow decline setting in throughout Tuesday 1st and Wednesday 2nd August.

Latest virtual buoy runs for Bali show an upswing in SSW groundswell over the coming week, with plenty more in store for early August. Source: Wave Tracker.

Latest virtual buoy runs for Bali show an upswing in SSW groundswell over the coming week, with plenty more in store for early August. Source: Wave Tracker.

Long range
Beyond that, there are good indications we’ll see a couple of deep, winter-scale lows developing over the south-western Indian Ocean giving rise to a couple of large to very large episodes during the first week of August. The first of these is projected to generate 30 to 40ft seas and swell as it pushes deep below Madagascar later this week.

The system is projected to remain quasi stationary southwest of the Kerguelen Islands on Thursday and Friday before pushing out below Heard Island and into the south-eastern Indian Ocean this weekend. Going on latest GFS guidance, this system will support a large area of 30 to 35ft seas and swell as it tracks up towards Indonesia over this time-frame. A long-period SSW groundswell arising from this source would start to make landfall at low levels on Wednesday 2nd, ahead of the bulk of swell hitting on Thursday 3rd. For now this is shaping up as another heavy, winter-scale episode peaking in the 8 to 10ft plus range – but this remains storm-dependent, so stay tuned to next week’s update for confirmation on this.

However, it’s the second, deeper storm system developing directly below South Africa that holds similar or even larger SSW swell-potential for Indonesia over the weekend of Saturday 5th August. This mid-latitude system is projected to rapidly intensify beloe South Africa over the weekend; setting up 40 to 60kt core winds around its upper western quadrant. The storm is projected to maintain similar or slightly weaker wind-speeds as it migrates below Madagascar on Sunday 30th July, followed by a weakening trend as it moves below the Kerguelen Islands on Monday 31st.

Latest Wave Tracker projections pick up two major storm-systems effecting the southern Indian Ocean during the final days of July. This holds good potential for two large SSW groundswells for Indonesia during the first week of August. Source: Wave Tracker.

Latest Wave Tracker projections pick up two major storm-systems effecting the southern Indian Ocean during the final days of July. This holds good potential for two large SSW groundswells for Indonesia during the first week of August. Source: Wave Tracker.

Going on latest GFS runs, this broad-scale storm will drive maximum significant wave heights into the 40 to 50ft realm over this time frame; in turn spawning another extra-large SSW groundswell for Indonesia over the weekend of Saturday 5th August. However, at this early stage there’s clear model divergence lending uncertainty to these projections. Corresponding EC runs are initially heavily downplaying wind-speeds and resulting swell-potential linked to this system – at least until it moves below the Kerguelen Islands early next week. Hence at this early stage there are high chances for significant revisions to both the size and timing of this prospective swell-event – stay tuned for an update on how this will play out in next Tuesday’s forecast.


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