Bali, Indonesia Surf Forecast 20 - 30 April, 2016

19 Apr 2016 0 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH FORECAST | Bali - Indo Forecast 

Forecast Issued Tuesday, 19 April 2016

There’s a string of really good surfing days lining up inside Indonesia’s swell window. This is the kind of forecast that makes me want to book a flight at short-notice – just to spend four or five days surfing perfect lefts in the 3 to 6ft range – and then high-tail it back home, with barely anyone knowing you’ve been gone. 

SEE ALSO: Best Line-Up Ever, New Zealand

Late April is starting to look more like the Indonesia we come to expect through the middle of autumn. Photo: CW user Jeffro.

Late April is starting to look more like the Indonesia we come to expect through the middle of autumn. Photo: CW user Jeffro.

Short Forecast

An overnight drop in SSW groundswell levels off around 2 to 3ft across exposed breaks on Wednesday, preceding the arrival of a new SSW groundswell building in throughout Thursday. Expect a peak around the 3 to 5ft mark on Friday before easing marginally by Saturday. This is superseded by a second, larger SSW groundswell peaking Sunday and slowly easing again early to mid next week.

SEE ALSO: Coastalwatch Plus Exclusive, The Surfing World Issue 372 Digital Edition

Daily Summary

Wednesday 20
Small SSW swell. Sets to 2 - 3ft exposed breaks. WIND: Light and variable tending ESE 5 to 10 knots.

Thursday 21
Small, reinforcing SSW groundswell. Around 2 – 3ft exposed breaks, bumping up towards 3 – 4ft during the day. Grading smaller elsewhere depending on exposure and easing into the afternoon. WIND: Early light and variable tending ESE 10 to 15 knots.

Friday 22
SSW groundswell peaks. Sets to 3 – 5ft exposed breaks, grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE 5 to 15 knots.

Saturday 23
New SSW groundswell. Sets to 3 - 4ft exposed breaks early, bumping up during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE 10 to 15 knots.

Sunday 24
New SSW groundswell. Sets to 4 – 6ft exposed breaks. Grading smaller elsewhere. WIND: Light and variable tending ESE 10 to 15 knots.

Monday 25
Easing SSW groundswell 4 – 6ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE around 5 to 15 knots.

Overview

There’s been a notable upswing in storm activity throughout the southern Indian Ocean since last week’s update – and that bodes well for surfers venturing to Indonesia during back third of April. In the first instance conditions are set to remain pretty subdued into the middle of the week as an easing SW swell drops down into the 2 to 3ft range on Wednesday. However, from Thursday onwards we can look forward to a series of overlapping SSW groundswells arriving throughout the Archipelago; pushing surf heights up to stronger 3 to 6ft levels for several days.

This activity commences with the arrival of a new SSW groundswell on Thursday. The source was a moderate strength polar low that intensified below Madagascar last Wednesday and Thursday; briefly establishing a narrow belt of zonal gales over the south-western Indian Ocean before weakening out last Friday. As the leading edge of this pulse fills in during the day expect set waves to nudge up into the 3 to 4ft range across exposed breaks – and it should hang in around this size early on Friday.

Just as this episode eases we have a new, reinforcing episode set to overlap with the older swell during Friday, with a peak anticipated to reach 4 to 6ft this weekend. The origin was a complex polar low that set up below South Africa late last week before intensifying as it traversed below Madagascar and out across the southern Indian Ocean last Sunday and Monday. An analysis of surface winds indicates the low closely followed forecast guidance; generating a broad areas of 30 to 40kt WSW gales extending west of the Kerguelen Islands over this time frame. However, the system was also characterised by a series of embedded frontal progression moving west to east through the storm system centred below Madagascar – effectively giving rise to a series of overlapping pulses of long-period SSW groundswell.

A first, leading pulse associated with this storm system is on track to arrive across Indonesian coasts on Friday ahead of the bulk of swell filling in on Saturday 23 April; probably producing a full day of 3 to 5ft surf across exposed reefs. This is backed up by a second, larger pulse that’s on track to peak at larger 4 to 6ft levels on Sunday and early Monday before gradually scaling down from there. The good news is any drop in size is likely to be marginal, with another strong round of SSW groundswell likely to maintain surf at mid to large levels across the region into the second half of next week.

This hinges on the rapid intensification of a new, compact storm system that’s forecast to develop southwest of the Margaret River region this weekend. Going on latest  GFS runs, the low sets up a compact area of SSW gales late Saturday/ early Sunday, with the head of the fetch positioned roughly 1,800 nautical miles south of Bali. Hence, the resulting swell looks acutely south in direction – and this will translate into widely varying surf-heights as the swell fills in – initially starting to show late Wednesday before peaking early on Thursday 28 April, speculatively in the 4 to 6ft range. It’s worth keeping in mind that this swell-source will quickly move into Western Australia’s swell shadow on Sunday – so whatever S groundswell does arrive will be short lived; probably fading to much lower levels by Friday 29 April.

Latest virtual buoy readings for Bali reflect the modest building trend in SSW groundswell underway over the coming week.

Latest virtual buoy readings for Bali reflect the modest building trend in SSW groundswell underway over the coming week.

Long Range

Regardless of how the aforementioned S pulse pans out, there are good indications we’ll see series of new groundswells backing up the tail end of this pulse late next week. The first prospective swell-source is a moderate strength polar low forecast to develop below Heard Island on Saturday before tracking out below Indonesia on Sunday. The storm is projected to support a broader area of low-end WSW gales across the south-eastern Indian Ocean; giving rise to a mid-period SSW swell speculatively filling in on Saturday 30 April in the 3 to 4ft plus range.

The next significant swell-event forecast for the Archipelago is one to keep track of. This event has its origins in the furthest south-western fringes of Indonesia’s swell window: deep in the southern Atlantic Ocean. Over the last 48 hours a large, complex extratropical low took shape over the region; giving rise to a phenomenal SW/WSW fetch exhibiting maximum speeds of 40 to 50 knots. Going on latest WW3 runs, the storm will drive maximum significant seas and swell to peaks of 40 to 50ft over the next 24 hours before the system begins to fill. The first, key observation to make about this source is the incredibly vast distance from Indonesia. Taking the most easterly point of projected maximum significant wave-height, a SW groundswell travelling out from this source must cover over 6,700 nautical miles before making landfall across Indonesian shores.

Remoteness aside, the high-end peak wave periods of 20 plus seconds associated with this groundswell will minimize energy loss, producing a significant round of long-period SSW groundswell tracing a Great Circle Path to Indonesia over the course of next week. Going off latest model runs, the leading edge of the groundswell should start to show throughout Thursday 28 April, preceding the bulk of swell peaking on Friday 29 and Saturday 30 April at solid levels; speculatively generating well organised, albeit inconsistent sets in the 3 to 5ft range at breaks focussing the groundswell. This will become clearer in next week’s update.

Monday's Southern Hemisphere MSLP chart depicts the deep extratropical low responsible for an ultra-long range SSW groundswell late this month.

Monday's Southern Hemisphere MSLP chart depicts the deep extratropical low responsible for an ultra-long range SSW groundswell late this month.

A recent satellite pass depicts the vast, 40 to 50kt fetch generated by the storm over the South Atlantic. Source: NOAA

A recent satellite pass depicts the vast, 40 to 50kt fetch generated by the storm over the South Atlantic. Source: NOAA


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