Bali, Indonesia Surf Forecast 12 - 24 September, 2018

11 Sep 2018 1

Ben Macartney

Chief Surf Forecaster

Surf Forecast issued 1.00pm, Tuesday, 11 September 2018

September is often a great month to be surfing across Indonesia – and this year presents a good case in point. In what’s been a fairly extreme season with respect to surf highs and lows, the coming week or two delivers consistently sizeable surf under light winds; for the most part ranging anywhere from 3 to 8ft across the major breaks for many days to come. As discussed in more detail below, this sustained run of surf originates from Indonesia’s south swell window – which has been highly active throughout early September. This activity looks like culminating in a larger, winter-scale event mid-next week, in all likelihood capping off an excellent first half of September with large surf in the 6 to 10ft range.

Early to mid September is on the pump across Indonesia. Photo: World Surfaris.

Daily Summary

Wednesday 12
SSW groundswell peaks under light winds. Sets ranging from 4 to 6ft exposed breaks, easing marginally during the afternoon and grading smaller elsewhere depending on exposure. WIND: Early light and variable tending S up to 10 knots during the afternoon.

Thursday 13
Leftover SSW swell reinforced by new SSW groundswell. Sets around 4 to 6ft+ exposed breaks, peaking at 5 to 8ft later. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending light S up to 10 knots later.

Friday 14
Solid SSW groundswell continues to range from 5 to 8t exposed breaks early, easing marginally during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE around 10 knots during the afternoon.

Saturday 15
SSW groundswell hangs in around 4 to 6ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE 5 to 15 knots.

Sunday 16
Reinforcing SSW groundswell. Solid sets to 5 to 6ft+ exposed breaks, grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE around 10 to 12 knots.

Monday 17
Potential for larger SSW groundswell ranging from 5 to 8ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE around 10 knots.

Tuesday 18
Easing SSW groundswell speculatively 4 to 6ft exposed breaks early, dropping a foot or two during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE 10 to 15 knots.

Wednesday 19
Speculative potential for large SSW groundswell building throughout the day. Potential for 4 to 6ft+ sets exposed breaks early, rising to 6 to 8ft during the day and potentially 8 to 10ft later. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE to 10 to 15 knots.

Overview
Well, if you had your pick, the coming week to ten days is arguably shaping up as one of the best surfing-windows of the season across Indonesia; both with respect to size, consistency and local winds. Further, the entire outlook period features a fairly acute swell direction; mostly ranging from 200 to 210 degrees; which is undoubtedly excellent for many of Indonesia’s famed breaks.

This energetic phase in swell-activity is linked to an active storm-track that’s been in place over the south-eastern Indian Ocean throughout early September; owing to a persistent and large high pressure system occupying the central-western Indian Ocean. This dominant synoptic feature has been steering the storm-track east to north-eastward towards Western Australia and Indonesia.

The end result is a constant stream of successive SSW groundswells inbound over the coming week to ten days; commencing with a building trend in wave-heights throughout Tuesday, leading in a first peak in the 4 to 6ft plus range across exposed breaks on Wednesday 12^th. The other key thing to note here is a temporary lull in ESE tradewinds resulting in a couple of days of light winds, tending light to moderate south both on Wednesday and Thursday afternoons – and this may take the shine off some of the major west facing reefs that really need the trades to fire up.

During Friday we should begin to see a return to light south-easterly trade-winds across the region and this should lead in stronger ESE winds in the 10 to 15 knot range this weekend and over the course of next week. Over this entire period we’ll continue to see successive pulses of mid to large SSW groundswell lighting up The Archipelago; mostly ranging from 3 to 8ft for many days to come.

Latest Bali Virtual Buoy readings show non-stop SSW groundswell inbound across Indonesia over the next five days, with more in the tank over the course of next week.

Long Range
Based on latest GFS model runs, this active phase in SSW swell will culminate in a larger, winter-scale episode peaking across the region mid-next week. This hinges on a deep extratropical low that’s forecast to rapidly intensify as it tracks across the Kerguelen Islands on Thursday. If this model guidance proves accurate, the low will generate 40 to 50knot plus SW winds as it moves across the south-eastern Indian Ocean on Friday and Saturday before weakening as it moves below Western Australia on Sunday.

The subsequent SSW groundswell is loosely projected to start arriving on Wednesday 19^th, leading in a major increase in surf heights into the 8 to 10ft realm across exposed breaks during the afternoon and potentially holding at similarly large levels early on Thursday 20^th. For now this all remains contingent on how the low evolves compared to forecast guidance. For now, corresponding EC runs are in reasonably good agreement with the GFS solution, so confidence for a large SSW swell event mid to late next week is deemed better than average.

However this pans out, it looks like the aforementioned blocking high will exert a blocking influence on further storm-development as it migrates further east early to mid next week. That means next Wednesday and Thursday’s major SSW swell-event may well be followed by a steady easing trend into the end of the week; speculatively culminating in a return to increasingly small to tiny surf across the region throughout the week of Monday 24^th.

Long range model runs pick up another impressive storm moving into Indonesia's south swell window into Friday and the weekend, setting up a larger, winter scale SSW groundswell for mid next week. Source: Wave Tracker.