Bali, Indonesia Surf Forecast 26 April - 10 May 2016

26 Apr 2016 0 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | Bali, Indonesia Surf Forecast

Forecast Issued Tuesday, 26 April, 2016

While we’re yet to see any major, winter-scale swell events impacting Indonesian shores this season, there’s still no shortage of surf on-tap into the final days of April and early May.

The short-term outlook sees a large pulse of SSW groundswell inbound across the region – and the tail end of it should see several days of excellent, mid-sized surf prevailing throughout the Archipelago. With the onset of the dry season we’re also beginning to see a marginal strengthening of ESE trade winds this week – still punctuated by early light and variable conditions and not exceeding 10 to 15 knots – and this will continue to produce good to excellent conditions across the major breaks for the foreseeable future.

Long, glassy swell-lines abound across the Archipelago into the end of April. Photo: CW user Ticka.

Long, glassy swell-lines abound across the Archipelago into the end of April. Photo: CW user Ticka.

Short Forecast

The arrival of a stronger SSW groundswell sees larger 4 to 6ft sets on Wednesday morning, building to a larger peak during the day. This episode hangs in at similar levels on Thursday morning before gradually subsiding; levelling off around the 3 to 4ft mark across exposed breaks on Friday before fading to lower levels over the weekend of Saturday 30 April.

Daily Summary

Wednesday 27
New SSW groundswell builds in. Sets to 4 - 6ft exposed breaks, building to 5 – 6ft+ during the afternoon. WIND: Light and variable tending ESE 10 knots.

Thursday 28
Easing SSW groundswell. Sets ranging from 4 – 6ft exposed breaks early, easing to 3 – 5ft during the day. Grading smaller elsewhere depending on exposure and easing into the afternoon. WIND: Early light and variable tending ESE 10 to 12 knots.

Friday 29
Leftover SSW groundswell. Inconsistent sets to 3 – 4ft exposed breaks, grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE 10 to 15 knots.

Saturday 30
Faded SSW swell reinforced by small, long period SW groundswell. Inconsistent sets to 2 - 3ft+ exposed breaks, fading during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE 10 to 12 knots.

Sunday 1
Small-scale SSW groundswell. Sets to 2 – 3ft exposed breaks. Grading smaller elsewhere. WIND: Light and variable tending ESE 10 knots.

Monday 2
New SSW groundswell builds in. 3 – 4ft exposed breaks early, building to 4 – 6ft. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE around 5 to 15 knots.

Overview

Tuesday saw another day of solid 3 to 5ft sets on offer across exposed reefs and there’s a whole lot more in store over the next few days. Wednesday marks the arrival of stronger round of SSW groundswell, building into the 4 to 6ft range from a strong southerly directional band of 210 degrees. The source is a cut-off low that developed below Indonesia, southwest of the Margaret River region over the weekend; briefly supporting a compact area of 30 to 40kt SSW gales late Saturday/ early Sunday, with the head of the fetch positioned roughly 1,800 nautical miles south of Bali.

The bulk of the resulting groundswell should be evident early on Thursday at a solid 4 to 6ft across exposed breaks, with scope for a larger peak in size occurring during the day/ afternoon. However, as projected in last week’s model runs, the swell source moved quickly into Western Australia’s swell shadow on Sunday night – and hence, this episode will be relatively short-lived; initially hanging in around 4 to 6ft max early on Friday before dropping steadily throughout the day. By Saturday expect much smaller leftovers y fading to lower 3 to 4ft levels by Friday 29 before fading to 2 to 3ft by Saturday.

Over the same time frame, there’s also a tiny, underlying SW groundswell in the water exhibiting exceptionally high peak wave periods. As discussed last week this originated from the furthest south-western fringes of Indonesia’s swell window, deep in the southern Atlantic Ocean early to mid last week.  This large, complex extratropical low took shape over the region on Monday 18 and Tuesday 19 April; giving rise to a phenomenal SW/WSW fetch exhibiting maximum speeds of 40 to 50 knots. The fetch generated maximum significant seas and swell to peaks of 40 to 50ft on Wednesday before the system begins to fill. However, the incredibly vast distance of this source from Indonesia has heavily diluted swell potential for the region.

As the leading edge of this energy begins to fill in on Thursday morning at peak periods of 24.5 seconds, it will have covered over 6,700 nautical miles across both the South Atlantic and the entire Indian Ocean – and hence associated wave height is only tiny; peaking at 2ft @ 20 seconds as the bulk of swell shows up on Friday. Regardless of these impressive peak intervals, the small-scale of the swell should keep surf-potential to a minimum – probably only generating very infrequent 2 to 3ft sets that will be hidden beneath a still dominant SSW swell. Still, the unusual nature of this episode may have some unforeseen effects at breaks that focus deepwater groundswells.

Bali, offshore virtual buoy point: 9° 0' 0"S x 115° 0' 0"E 

Latest virtual buoy readings for Bali depict a strong round of SSW groundswell peaking on Wednesday and Thursday eases to much lower levels this weekend.

Latest virtual buoy readings for Bali depict a strong round of SSW groundswell peaking on Wednesday and Thursday eases to much lower levels this weekend.

Beyond that, the synoptic pattern becomes increasingly dominated by a slow moving high-pressure system setting up over the southern Indian Ocean over the course of next week. As the high builds in strength,north of Heard Island on Tuesday and Wednesday it steers a series of frontal progressions northeast, towards Australia’s Southwest corner – and this holds definitive potential for another substantial round of SSW groundswell filling in early next week. This is based on latest GFS runs picking up a vigorous polar low intensifying below Heard Island  on Wednesday before tracking northeast on Thursday. The system is projected to support a broad area of 30 to 45kt SW gales as it sweeps up towards south-western Australia on Thursday. These winds act upon an already active sea state to generate 25 to 35ft peaks in seas and swell late Thursday/ early Friday. 

Based on this guidance, a SSW groundswell spreading out off this source fills in on Monday and Tuesday, generating peaks in the 4 to 6ft range across exposed breaks. This is contingent on how the low evolves, so there’s scope for changes to this scenario over the next few days. However it pans out, this system also sets up on the far eastern periphery of our swell window, bounded by the West Australian coast. Hence, Monday and Tuesday’s peak size will invariably precede a steep decline in SSW swell by Wednesday 4 May.

Long Range

From mid to late next week we’ll be turning to our remote southwest swell window for a new, substantial round of SW groundswell that’s set to supersede the tail end of the SSW swell as it fades on Wednesday 4 May. This episode has remote origins; arising from a deep low-pressure system currently developing over the South Atlantic Ocean, well southwest of South Africa.

Over the next 48 hours the low carries a broad area of W gales eastward – again going to work upon a highly active sea-state prevalent in the wake of a previous system. This is forecast to drive maximum significant wave height to peaks of 30 to 35ft below South Arica by Wednesday afternoon. A SW groundswell travelling away from this source should arrive approximately one week later. This is preceded by a smaller SW pulse on Tuesday 3, ahead of a second, larger push into the 5 to 6ft plus range on Wednesday 4 and Thursday 5 May. This is also contingent on how the storm behaves compared to the GFS forecast, so revisions to the size and timing are a possibility in next week’s update.

Beyond that, it appears the aforementioned high-pressure system will progressively quash new swell potential for the region into early May. The high is forecast to expand in size as it remains quasi-stationary over the south-eastern Indian Ocean during the final days of April and early May and this will coincide with an absence of new storm development. If this proves accurate, the knock on effect will be a return to smaller scale surf over the weekend of Saturday 7 May; speculatively dropping into the 1 to 2ft range on Sunday 8 ahead of a new, mid to large SSW groundswell arriving on Monday 9 May. This is based on longer-term model runs picking up a significant activation of the long-wave trough below the Australian mainland during the first days of May, offering up potential for new round of directional S groundswell (190 to 210 degrees). The size and timing of this episode will become clearer in next week’s update.

The forecast development of a deep, complex low pressure system below the Australian mainland during the opening days of May presents good potential for a new S groundswell for Bali and surrounds early in the week beginning Monday 9 May.

The forecast development of a deep, complex low pressure system below the Australian mainland during the opening days of May presents good potential for a new S groundswell for Bali and surrounds early in the week beginning Monday 9 May.


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