Bali, Indonesia Surf Forecast 4 - 17 October, 2017

3 Oct 2017 1 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | BALI, INDO SURF FORECAST 

Surf Forecast issued 3.00pm, Tuesday, 3 October, 2017

It’s been business as usual across the island’s wide-ranging surfable coastline throughout late September and early October as mostly small-scale SSW swell rolls in under light and variable to light SE winds. Despite the impending eruption of Bali’s largest volcano, Mount Agung, this status quo will continue into the middle of October – or at least until the volcano does blow – which vulcanologists continue to say could be anytime soon. Putting the prospect of fire and brimstone raining down from above aside, the short-term surf forecast sees groundhog days of small surf under light winds – and assuming you keep your expectations in check this all sounds like pretty good fun across the most exposed Indonesian breaks. It looks like it won’t be until Tuesday/ Wednesday next week that we see a more robust SSW groundswell pushing surf-heights into the 3 to 6ft range – again under light and variable late season winds.

With Mount Agung threatening to blow her top, the Mentawaii Islands continues to look like a great late season destination. Photo: Andy Potts.

With Mount Agung threatening to blow her top, the Mentawaii Islands continues to look like a great late season destination. Photo: Andy Potts.

Short Forecast
Small-scale SSW swell hangs in around 2 to 3ft across exposed breaks all week, preceding the arrival of a larger round of SSW groundswell on Tuesday 10th and Wednesday 11th October.

Daily Summary

Wednesday 4
Small SSW swell. Slow sets to 2 – 3ft exposed breaks, fading later. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE 5 to 10 knots.

Thursday 5
Marginal leftover SSW swell reinforced by small, long-range SSW groundswell. Slow sets around 1 - 2ft early, bumping up to 1 – 3ft exposed breaks during the afternoon, inconsistent in the upper range. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE to SE 5 to 10 knots.

Friday 6
Small SSW groundswell fills in. Around 2 – 3ft exposed breaks, bumping up to 2 – 4ft during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE 5 to 10 knots.

Saturday 7
SSW groundswell hangs in around 2 - 4ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE 5 to 10 knots.

Sunday 8
Fading SSW swell. Slower sets to 2 – 3ft exposed breaks, grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE around 10 knots later.

Monday 9
New long period SSW groundswell fills in. Sets to 2 – 3ft+ exposed breaks, building to 3 – 4ft. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE around 10 knots.

Tuesday 10
SSW groundswell picks up. Around 3 – 4ft exposed breaks early, bumping up during the day. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SE to 10 knots.

Latest virtual buoy readings for Bali tell the same late-season story: groundhog days of small-scale surf under light and variable winds, ahead of a series of larger SSW pulses arriving over the weekend and over the course of next week.

Latest virtual buoy readings for Bali tell the same late-season story: groundhog days of small-scale surf under light and variable winds, ahead of a series of larger SSW pulses arriving over the weekend and over the course of next week.

Overview
Indonesia is now well and truly in the midst of a subdued phase in wave-activity; compliments of dominant mid-latitude highs over the central Indian Ocean, coupled with relatively subdued polar storm-activity mostly situated below 50S. Over the last few days another large, albeit weaker high slid west to east across the region as a new low set up over the south-western Indian Ocean, well south of Madagascar.

The knock on effect of the blocking pattern is a full week of small-scale surf; mostly ranging from 2 to 3ft across exposed reefs on Wednesday and Thursday, with scope for a slightly stronger pulse of groundswell nudging set waves into the 3 to 4ft range later Friday and on Saturday. This energy is projected to taper off again by Sunday, preceding the arrival of two new, overlapping pulses early to mid next week.

The first of these is derived from the aforementioned low south of Madagascar. A new round of SW groundswell spreading out off this source is forecast to make landfall on Monday at stronger peak interval of 15 to 16 seconds; generating stronger set waves in the vicinity of 3 to 4ft across exposed breaks.

This is closely followed by a series of overlapping SSW pulses; generated by rejuvenated storm-activity forecast to develop over the south-eastern Indian Ocean, below Indonesia and Western Australia throughout Thursday, Friday and the weekend. Again, this activity exhibits all the hallmarks of spring, rather than winter; for the most part generating maximum significant wave-heights of 20 to 25ft below the 40 S parallel. The upshot is scope for several days of solid, mid-sized SSW groundswell; picking up during Monday and holding size in the vicinity of 3 to 4ft plus across the major breaks throughout Tuesday 10th, Wednesday 11th and Thursday 12th October.

Long Range
Beyond that, latest model guidance picks up another large, intense polar low developing below South Africa over the next few days. Regardless of its impressive size and low central pressure, the broader westerly wind-fetch developing along its upper flank won’t exhibit particularly high speeds. Instead, the low establishes stronger 40 to 50kt pre-frontal NW winds in conjunction with a large high anchored southeast of Madagascar – and overall this pattern is forecast to inhibit associated swell-potential for Indonesia. Never the less, this isn’t all bad news. Based on this, we’re looking at a new, reinforcing SW groundswell building in around the 3 to 4ft mark on Friday 13th and holding this size over the weekend of Saturday 14th October.

Longer-term model runs then point to another large high pressure system setting up over the central Indian Ocean this weekend; sitting astride another deep polar low to the south. The good news is this low is forecast to intensify dramatically as it migrates into our south swell window around Monday 9th and Tuesday 10th setting up SSW to SW gales aimed more or less directly with Indonesian coasts.  For now the key models are at odds regarding the strength of the resulting wind-fetch and hence there’s still a high degree of uncertainty surrounding swell-potential. Still, the fact that both GFS and EC runs are picking it up is a good sign; providing good chances for some kind of mid to large SSW groundswell arriving around Monday 17th.. This will be reviewed again in next week’s update.


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