Bali, Indonesia Surf Forecast 19 - 30 September, 2018

18 Sep 2018 0 Share

Ben Macartney

Chief Surf Forecaster

Forecast Issued Tuesday, 18 September 2018

September has been good to surfers across Indonesia so far – and going on short term-modelling it’s clear that it will continue to deliver the goods as another powerful south-groundswell kicks in later this week. This is, however, likely to mark the last notable SSW groundswell for the month, preceding a short-term lull in notable swell-activity into late September. Of course Indonesia’s swell window is so large that there’s always another swell not too far off – and going on longer-term guidance the swell-focus is set to shift to Indonesia’s south-west swell window, following the evolution of a significant storm-system below Africa.

Empty late-season lineups beckon across Indonesia mid to late September. Photo: World Surfaris.

Empty late-season lineups beckon across Indonesia mid to late September. Photo: World Surfaris.

Daily Summary


Wednesday 19th
Fading SSW swell reinforced by rising SSW groundswell @ 205 degrees. Around 3 to 4ft+ across exposed breaks early, building towards 4 to 6ft+ during the afternoon, bigger later. WIND: Early light and variable tending SE around 5 to 10 knots during the afternoon.

Thursday 20th
SSW groundswell @ 205 degrees peaks at 6 to 8ft+ at the most exposed breaks early, easing towards 5 to 7ft during the afternoon. Grading smaller elsewhere with size depending on exposure. WIND: Light early, tending E to SE around 10 knots later.

Friday 21st
SSW groundswell further eases throughout the day. Initially 4 to 5ft+ sets exposed breaks, settling to 3 to 4ft+ during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE 10 to 15 knots during the afternoon.

Saturday 22nd
Leftover SSW swell around 2 to 3ft+ exposed breaks early before fading to 1 to 3ft into the afternoon. Grading smaller elsewhere with size depending on exposure. WIND: Light early, tending ESE to SE up to 10 to 15 knots during the afternoon.

Sunday 23rd  
Smaller scale SSW swell lingers around 1 to 2ft+ across exposed breaks, dropping into the afternoon. Grading smaller elsewhere depending on exposure. WIND: Light early, tending ESE up to 10 to 15 knots later.

Monday 24th
Background SSW swell up to a slow 1 to 2ft max exposed breaks, otherwise near-flat elsewhere. WIND: Early light and variable tending SE around 10 knots.

Tuesday 25th
Potential for small SSW groundswell. Speculatively 2 to 4ft across exposed breaks, grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending SE around 10 knots.

Wednesday 26th
Easing SSW groundswell up to 2 to 3ft+ across exposed breaks, easing later. Grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending SE about 10 knots.

Overview
The south-eastern Indian Ocean has been dishing up the goods throughout early to mid September; specifically in the form of strong SSW groundswells arriving out of a fairly acute southerly directional band. The good news is this pretty much sets the trend in the near-term, with yet another powerful powerful round of SSW groundswell now closing in on Indonesian shores. The origin is another intense mid-latitude low that rapidly intensified as it moved east of the Kerguelen Islands last Friday and Saturday; setting up a core WSW fetch exhibiting speeds of 40 to 55 knots before gradually weakening from Sunday onwards.

Long-period forerunners preceding the bulk of swell start to fill in early on Wednesday, leading in a strong building trend in wave-heights throughout the afternoon; probably reaching solid 4 to 6ft plus levels at the more exposed breaks with scope for larger sets showing late in the day. The bulk of swell holds peak size early on Thursday in the vicinity of 6 to 8ft ahead of a gradual easing trend setting in from there. This should see another great day of mid/ large SSW groundswell throughout Friday 21st before the tail end of this event drops into the 3ft range by Saturday 22nd – and by the looks of longer-term model guidance it’s well worth making the most this event before it starts to dry-up.

The aforementioned low that moved through Indonesia’s south-swell window last weekend marked a last burst of major storm-activity over the region preceding a significant weakening of the storm track this week. The knock on effect is likely to be increasingly tiny surf prevailing throughout Sunday 23rd, culminating in near-flat conditions by Monday 24th.

From there, there’s good chances for a modest upswing in SSW swell on Tuesday 2th and Wednesday 26th; optimistically reaching 2 to 4ft across exposed breaks. This originates from a moderate strength low forecast to move through our south swell window over the next 48 hours; setting up a mid-period pulse out of the 200 degree band. As discussed below, it looks like the swell-focus will shift to Indonesia’s more remote southwest swell window into the end of September and early October.


Latest virtual buoy readings for Bali show another powerful round of south groundswell is on track to light up the region into the end of the week.

Latest virtual buoy readings for Bali show another powerful round of south groundswell is on track to light up the region into the end of the week.

Long Range
Looking further out to the final days of September into early October there’s emerging potential for a mid-sized, high period SW groundswell arriving across the Archipelago. This is linked to a broadscale low forecast to intensify over the far south-eastern Atlantic on Thursday before tracking slowly eastward, deep below Africa on Friday – and eventually out into the south-western Indian Ocean this weekend. Throughout this period the storm is projected to maintain a broad 30 to 50 knot WSW fetch, primarily situated between 40S and 55S.

Although the storm gives rise to a vast area of 30 to 45ft seas, the vast distance of this source from Indonesia will keep a lid on the size of the groundswell via wave erosion and attenuation. The leading edge is projected to start filling in at intervals of 20 to 22 seconds on Friday; initially at very low-levels preceding the bulk of swell filling in over the weekend of Saturday 29th. For now this is shaping up as a 4 to 6ft peak across exposed areas, with long-waits between sets. Having said that, the high projected peak intervals of 18 seconds typically result in wider than usual variances in surf-heights as those locations focussing the deep-water energy pull in significantly larger sets, while substantially by-passing others.

Beyond that, the models show loose agreement on a still active, but lower-strength storm-track setting up a succession of small to mid-sized SW swells for Indonesia into the first week of October. The specifics on these will become clearer in next week’s update.

The evolution of a deep low below South Africa later this week holds good potential for a long-interval SW groundswell for Indonesia, arriving during the final days of September.

The evolution of a deep low below South Africa later this week holds good potential for a long-interval SW groundswell for Indonesia, arriving during the final days of September.


Tags: Indo Surf Forecast , Ben Macartney (create Alert from these tags)

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