Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Tue 26th Aug)

Best Days: Thursday onwards (experienced surfers only during the large swell)

This week and weekend (Aug 27 - 31)

After one of the largest and strongest pulses of S/SW groundswell for some time across the Ments on Sunday a slow drop in size has been seen through yesterday and further today with less than favourable W-NW winds from the Ments north.

South Sumatra has performed better with fresh SE trades for the most part.

We'll continue to see the swell tail away through this afternoon and bottom out tomorrow morning across the region before a secondary large and powerful S/SW groundswell arrives late in the day.

This secondary large swell was generated by another vigorous polar low firing up from the Polar Shelf under the influence of a strong amplification of the Long Wave Trough, aiming a fetch of severe-gale SW tending W/SW winds towards WA with stronger storm-force winds recorded at its core.

The swell will be a touch under the size we saw Sunday and have more south in it but still come in very large and strong at its peak Thursday morning with 8ft to occasionally 10ft sets at exposed spots in the Ments, smaller surf up at Nias and the possibility of the odd bigger 12ft bomb in South Sumatra.

A drop in size should be seen into the afternoon and more noticeably through Friday and Saturday.

Winds on Thursday won't be great in the Ments and will still be moderate from the NW, while South Sumatra should see variable winds from the S'th.

On the backside of the swell though, conditions look great with weak E'ly trades becoming variable into the weekend across Ments, while South Sumatra should offer moderate E/SE-SE winds.

Into Sunday the easing trend will be halted temporarily as an inconsistent long-range S/SW groundswell arrives, but no major size above 5ft is due in the Ments.

Next Monday onwards (Sep 1 onwards)

Unfortunately the longer term isn't too flash with a large blocking high setting up across our prime swell window in the Western Indian Ocean. This will focus the frontal activity more towards WA and in our southern swell window, but there isn't due to be any major storm developments. Therefore next week will see the surf bottoming out into the middle to end of the week, with some better swell on the cards for the following Sunday. More on this Thursday though.

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