Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Thursday 11th Jun)

Best Days: Every day over the coming period besides Monday afternoon

This week and next week (Jun 12 – Jun 19)

We've fallen in between swells today across the region, but we've got a fun S/SW groundswell on the cards for tomorrow and the weekend, with a larger S/SW groundswell later next week.

Tomorrow and Saturday's S/SW groundswell was generated by an intense cut-off low in the Indian ocean and should provide good 5-6ft+ waves at exposed spots once it fills in tomorrow, easing from a similar size Sunday morning. Southern Sumatra should see more of those bigger sets during the peak of the swell.

A gradual drop is then expected into Sunday and further Monday, bottoming out into the evening.

Conditions should be generally favourable with light variable winds, taking a slight NW bias through Saturday before easing again into Sunday, so keep this in mind.

Into next week some background S/SW groundswell should build Tuesday and hold Wednesday, offering inconsistent 3-4ft+ sets across exposed breaks as weak SE trades start to develop, stronger around Southern Sumatra.

Of greater importance is a large and good S/SW groundswell due to build later Wednesday and peak Thursday across the region.

A broad and strong polar frontal progression is firing up south-east of South Africa, and should aim a fetch of severe-gale W/SW winds through our swell window while tracking slowly east.

A large S/SW groundswell event should be seen off this low, with the swell arriving later Wednesday, building to a peak through Thursday to 6-8ft across exposed breaks, with the possibility of the rare bigger bomb.

A drop in size is then due through Friday and further into the weekend as the SE trades slowly relax (and swing more E/SE around Southern Sumatra).

Beyond this a broad cut-off low is forecast to develop in the Indian Ocean, setting up a broad block across our main swell window resulting in a slow run of surf heading into the end of the month. This may break down into the end of the month, with a large S/SW groundswell possible for the final days of June, but we'll review this on Tuesday.

16 day Mentawai forecast graph
16 day Nias forecast graph
16 day South Sumatra forecast graph