Bali, Indonesia Surf Forecast 26 September - 10 August, 2018

25 Sep 2018 2 Share

Ben Macartney

Chief Surf Forecaster

Forecast Issued Tuesday, 25 September 2018

The final days of September continue to deliver great conditions to the entire Indonesian Archipelago, as a late flurry of SW groundswell coincides with a slackening tradewind-regime. That should translate into a much broader range of good surfing options as mostly light winds of 5 to 10 knots open up clean conditions across various coasts open to most points of the compass (bar north, of course). In conjunction with a predominant swell direction of 220 degrees, that should see a multitude of clean surfing options opening up along many an exposed coast between Sumatera and Sumba – at least until tradewinds begin to rebuild towards 10 to 15 knots early to mid next week.

Good surfing options about across Indonesia throughout late September. Photo: World Surfaris.

Good surfing options about across Indonesia throughout late September. Photo: World Surfaris.

Daily Summary

Wednesday 26th
Mix of long range SSW and SW groundswells from 210 to 220 degrees. Ranging from 2 to 3ft across exposed breaks, inconsistent in the upper range and bumping up marginally during the afternoon. WIND: Light and variable tending SE around 5 to 10 knots during the afternoon.

Thursday 27th
Long range SW groundswell @ 220 degrees peaks at 2 to 4ft at the most exposed breaks grading smaller elsewhere with size depending on exposure. WIND: Light early, tending S to SE around 5 to 10 knots later.

Friday 28th
Fading SSW groundswell underpinned by long-period SW forerunners throughout the day. Initially 2 to 3ft+ sets exposed breaks, settling to 2 to 3ft during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending SSE to 10 knots during the afternoon.

Saturday 29th
Leftover SSW swell reinforced by long period SW groundswell throughout the day. Initially ranging from 3 to 5ft exposed breaks, building to 4 to 6ft during the day. Grading smaller elsewhere with size depending on exposure. WIND: Light early, tending SSE 5 to 10 knots during the afternoon.

Sunday 30th
Long range SW groundswell builds, inconsistent sets ranging from 3 to 5ft+ across exposed breaks, easing during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Light early, tending S 5 to 10 knots later.

Monday 1st
Easing SW groundswell. Slow 3 to 4ft sets exposed breaks, grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending SSE around 10 knots.

Tuesday 2nd
Fading SW groundswell. Speculatively 2 to 3ft across exposed breaks, grading smaller elsewhere with size depending on exposure and dropping throughout the day. WIND: Early light and variable tending SE around 10 to 15 knots.

Wednesday 3rd
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
Over the coming week the surf-focus is fixed on our south-west swell-window as a couple of overlapping pulses arrive out of the 220 degree band. The first starts filling in at low-levels beneath pre-existing SSW swell on Wednesday and should show most size on Thursday and Friday in the 2 to 4ft range depending on location. As this episode gradually scales down again throughout Friday it starts to overlap with a new, longer-range episode, arriving at higher peak periods in excess of 20 seconds.

This impending episode is linked to a broadscale low that set up over the far south-eastern Atlantic last Thursday before tracking slowly eastward, deep below Africa on Friday 21st – and then out below Madagascar and across the south-western Indian Ocean over the weekend of Saturday 22nd September. Throughout this period the storm is projected to maintain a broad 40 knot WSW/ SW fetch, primarily situated throughout the mid-latitudes, bounded by 40S and 55S.

Although the storm supported 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. 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 could easily pull in significantly larger sets, while substantially by-passing others.

A high-period, long-range SW groundswell builds in across Indonesia this weekend, generating wide ranging surf options in the 3 to 6ft realm. Source: Wave Tracker.

A high-period, long-range SW groundswell builds in across Indonesia this weekend, generating wide ranging surf options in the 3 to 6ft realm. Source: Wave Tracker.

Long Range
The only notable prospective swell-source appearing on Indonesia’s long-term horizon is an intense polar low that’s forecast to develop over the far south-eastern Indian Ocean, roughly 3,000 nautical miles south of Sumatra early next week. This remote location places the source on the far south-eastern fringes of Indonesia’s swell window and based on latest GFS runs it looks substantial; speculatively supporting 40 to 50kt core winds as it migrates eastward across the region from Sunday to Tuesday.

However, the far southern location of the storm would result in an acutely south swell direction; commencing with leading forerunners in the 20 second range beginning to make landfall late Thursday, leading in the bulk of energy peaking across the region later Friday 5th through early Saturday 6th October before steadily dropping off again throughout Sunday 7th.

Beyond that, there’s some emerging consensus among the key models indicating a large and strong high pressure system will develop over the south-eastern Indian Ocean early to mid-next week; leading in another suppressed phase in swell-development into the second week of October. For now that hints at a return to small/ tiny surf approaching the 1 to 2ft range from Wednesday 10th to Friday 12th and beyond, but plenty can change between now and then.

This serious looking purple blob presents good potential for a new, long-interval S groundswell for Indonesia during the first week of October. Source: Wave Tracker.

This serious looking purple blob presents good potential for a new, long-interval S groundswell for Indonesia during the first week of October. Source: Wave Tracker.


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

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