Back-To-Back Swells About To Hit Indo!

6 Sep 2016 0 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH | Bali, Indo Forecast

Forecast Issued Tuesday, 6 September 2016

The Indian Ocean is alive with storm activity this week – and this is very good news if you happen to be inbound on a flight to Denpasar or Padang anytime soon. An active storm track in effect over the southern Indian Ocean has already set up a first, large SSW swell for this weekend – and this is forecast to go back to back with a smaller, albeit longer period SSW pulse early next week.

SEE ALSO: Why A Quick Surf Is Better Than What You're Doing Right Now

The good times keep rolling through early to mid September under the influence of overlapping SSW groundswells. Photo: Nick O'Brien.

The good times keep rolling through early to mid September under the influence of overlapping SSW groundswells. Photo: Nick O'Brien.

Short Forecast

Mid-sized SSW swell hangs in around the 3 to 4ft mark on Wednesday before fading to lower levels by Thursday. This precedes a strong rise in new SSW groundswell throughout Friday, rising to a peak in the 6ft plus range this weekend.

Daily Summary

Wednesday 7
New SSW groundswell. Sets around 3 - 4ft+ exposed breaks early, easing during the afternoon. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE 10 to 15 knots.

Thursday 8
SSW swell. Sets around 2 – 3ft+ exposed breaks. Grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending ESE 15 to 20 knots.

Friday 9
Small-scale SSW groundswell. Sets around 1 – 3ft exposed breaks, picking up to 3 – 4ft during the day and up to a larger 4 – 6ft+ during the afternoon. Grading smaller elsewhere with size depending on exposure. WIND: Early light and variable tending ESE 10 to 15 knots.

Saturday 10
SSW groundswell. Sets around 5 – 8ft exposed breaks. Grading smaller elsewhere depending on exposure. WIND: Light and variable tending ESE to SE around 5 to 10 knots.

Sunday 11
Easing SSW groundswell. Sets around 5 – 6ft exposed breaks early, easing to 4 – 5ft during the afternoon. Grading smaller elsewhere with size depending on exposure. WIND: Light and variable tending ESE 5 to 10 knots.

Monday 12
Leftover SSW swell reinforced by new, long-period SSW groundswell. Around 2 – 4ft exposed breaks early, rising to 3 – 4ft+ during the day. Grading smaller elsewhere depending on exposure. WIND: Early light and variable tending ESE 10 to 12 knots.

Overview

The month of September continues to look very active on the wave-front. Over the next seven to ten days we can look forward to the arrival of two significant SSW groundswells; variously generating powerful, winter-scale surf in the 4 to 8ft range. These major episodes are punctuated by a consistent run of mid-sized SSW groundswell that should see head high surf or bigger prevailing right through to the middle of the month.

Tuesday marked the arrival of a new, mid-sized pulse of SSW groundswell ranging either side of 4ft across exposed breaks – and this episode will continue to run at similar levels throughout Wednesday before easing a notch or two by Thursday. The last of this pulse fades to much lower levels by Friday morning; probably reaching a low-point of 2 to 4ft early in the day preceding the arrival of a new SSW groundswell throughout the afternoon. This impending increase marks the leading edge of the first, significant SSW groundswell that’s projected to peak over the weekend; showing maximum size on Saturday before starting to back off throughout Sunday.

The swell originates from a highly active storm-track that set up throughout the south-western Indian Ocean during the opening days of September; characterised by a series of vigorous frontal progressions traversing through polar latitudes. This activity culminated in the formation of a larger mid-latitude low over the south-central Indian Ocean on Monday and Tuesday; forming an expansive SW fetch in conjunction with a high situated southeast of Madagascar.

Although associated wind-speeds aren’t overly strong (mostly 30 to 40 knots), the impressive length and duration of the fetch coupled with its direct alignment with Indonesia points to a substantial SSW pulse; peaking in the 5 to 8ft range across the major reef-breaks on Saturday before easing into the 4 to 6ft range by Sunday. Over the same time-frame we have a late reinvigoration of ESE tradewinds lending the focus to the major west-facing reefs from Wednesday to Friday, preceding a return to lighter winds in the 5 to 10 knot range this weekend.

Sunday afternoon is shaping up as an interim low-point in surf throughout the region preceding the arrival of the second major swell-event filling in on Monday 12th September. This event exhibits longer peak intervals of 18 to 20 seconds at its leading edge and also arrives from a more acute southerly direction of 200 degrees. The source is a vigorous polar low forecast develop directly below the Kerguelen Islands on Wednesday before rapidly intensifying as it traverses eastward across the southern Indian Ocean on Thursday. The low’s central pressure is projected to fall into the low 930’s over this time frame; giving rise to a steep pressure gradient in conjunction with a large high anchored over the central Indian Ocean. The resulting WSW fetch squeezed between these systems should generate core wind-speeds of 40 to 55 knots, embedded within a more expansive area of 30 to 40 knot winds – together encompassing a vast region spanning latitudes bounded by 40S and 60S.

SSW groundswell arising from this source is projected to fill in on Monday morning, producing a steady building trend in surf-heights as the day progresses. Having said that, it’s onset is likely to be slow to begin with, with long lulls between leading forerunner sets. However, by the afternoon it’s likely to be pulsing into the 4 to 6ft range across exposed breaks and it should maintain similarly large surf into Tuesday morning before gradually scaling down again into the afternoon. Given this pans out as current model guidance suggests, expect moderating leftovers in the 3 to 4ft range by Wednesday 14th, preceding a further drop to 2 to 3ft by Thursday 15th September. Given this is storm-dependant, there’s still plenty of scope for changes to this scenario as the week progresses.

Latest offshore virtual buoy readings for Bali: A couple of days of mid-sized SSW precede the arrival of a larger pulse from Friday to Sunday.

Latest offshore virtual buoy readings for Bali: A couple of days of mid-sized SSW precede the arrival of a larger pulse from Friday to Sunday.

Long Range

There are now firming signs among long-range computer modelling pointing to the arrival of a small to mid-sized SW groundswell on Friday 16th – and this may be a precursor to a larger pulse filling in over the weekend of Saturday 17th September. This hinges on renewed storm-genesis occurring throughout the south-western and south-central, Indian Ocean over the course of this weekend and early next week. This commences with a series of frontal progressions marching below Madagascar Thursday/ Friday, preceding the development of a larger, moderate strength low west of the Kerguelen Islands this weekend. Based on latest GFS runs, the low will generate maximum significant wave heights of 30ft over the region on Sunday; giving rise to a mid-sized pulse of SW groundswell over the weekend of Saturday 17th; speculatively peaking in the 3 to 5ft range.

Beyond that, both long-term GFS and EC modelling points to a period of subdued storm activity throughout the southern Indian Ocean into the middle of next week. If this proves accurate, we can expect a lull in wave-action throughout the Archipelago over the course of the week beginning Monday 19th September; characterised by declining SW swell; speculatively bottoming out in the 1 to 2ft range between Wednesday 21st to Friday 23rd

Tags: ben , macartney , forecast (create Alert from these tags)

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