Indo Swell Alert: Wednesday, 26 August 2015

26 Aug 2015 0 Share

Ben Macartney

Chief Surf Forecaster

Indo Swell Alert: August 24, 2015

In the wake of long hiatus in significant swell-events since the heavy SW groundswell that rocked the Indonesian Archipelago in late June, there is at long last another winter-scale swell event on the forecast horizon. Over the last 48 hours the southern Indian Ocean has finally reactivated in spectacular fashion; spawning a low pressure system of impressive dimensions over a remote polar region. A long-interval SSW groundswell emanating from the storm is already closing the distance on Indonesian shores. View the Coastalwatch Wave Tracker

Latest Wave Tracker model runs pick up a the leading edge of the SSW groundswell inbound atn peak intervals of 20 seconds plus. These forerunners begin to show throughout Monday August 31st ahead of the bulk of swell hitting on Tuesday, September 1st.

Latest Wave Tracker model runs pick up a the leading edge of the SSW groundswell inbound atn peak intervals of 20 seconds plus. These forerunners begin to show throughout Monday August 31st ahead of the bulk of swell hitting on Tuesday, September 1st.

In Short

  • A deep extratropical low positioned over the far southern Indian Ocean supported a vast area of WSW gales across polar latitudes on Tuesday and Wednesday, driving maximum significant wave heights to peak of 30 to 40ft.
  • A long-interval SSW groundswell spreading out from the source begins to arrive across Indonesian coasts during Monday 31st August, triggering a steady building trend in surf heights throughout the day.
  • The episode is expected to peak throughout Tuesday, generating large 8 to 10ft sets across the premier Indonesian breaks like Uluwatu under moderate ESE tradewinds.
  • The tail end of the groundswell should continue to generate larger surf throughout the Archipelago on Wednesday 2nd September.

Wednesday's MSLP chart depicts the intense Southern Ocean low situated directly south of the Kergulen Islands, over 3,700 nautical miles southwest of Bali. Source: BOM.

Wednesday's MSLP chart depicts the intense Southern Ocean low situated directly south of the Kergulen Islands, over 3,700 nautical miles southwest of Bali. Source: BOM.

Overview
The evolution of an intense polar low below South Africa on Monday marked the early stages in the evolution of a large extratropical low over the southern Indian Ocean. The development of the system follows in the wake of a first, broad frontal low that’s set to weaken as it migrates east. The system began to intensify below Madagascar on Tuesday morning before rapidly intensifying as it tracked east, giving rise to a vast area of gales – initially aligned WNW ahead of the developing low before re-aligning WSW in it’s wake. This latter wind-fetch increased in strength as the low intensified south of the Kerguelen Islands on Wednesday, with satellite passes confirming a vast area of 30 to 50kt WSW gales extending about 1,300 nautical miles across the Southern Ocean. The fetch drives maximum significant wave heights up into the 40 to 50ft range near the core of the system on Wednesday evening. Although the bulk of this deep-water swell is directed west, below the Australian mainland, it sends a powerful pulse of high-energy SSW groundswell northeast towards Indonesia from Thursday onwards.

The leading forerunners associated with this deepwater groundswell should begin to make landfall at peak intervals of 20 to 24 seconds on Sunday night, leading in a steady building trend in surf-heights throughout Monday 31 August. Initially older SSW swell should still be dominant in the 4 to 6ft range across exposed breaks early, expect a much stronger push into the afternoon, with heavier 6 to 8ft sets likely as the sun dips below the horizon on Monday evening. This should lead in the bulk of the swell arriving overnight and it looks like it will be big; pushing into the 8 to 10ft range across the more exposed reefs like Uluwatu and G-Land, on September 1 (Tuesday morning) while producing excellent surf ranging anywhere from 4 to 8ft elsewhere. This episode is currently set to peak during the morning before beginning taper off late in the day and it should scale down into the 6 to 8ft range by the morning of Wednesday September 2nd.

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