Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Thu 28th Aug)

Best Days: Every day over the coming period until mid-late next week

This Friday through next week (Aug 29 – Sep 5)

A large and powerful S/SW groundswell showed later yesterday across the region and filled in strongly overnight, with large surf seen today across Western Indonesia.

Winds are a little funky though and variable in South Sumatra with less favourable NW winds from the Ments north.

Conditions should become great into tomorrow though as the swell drops away steadily, easing from 6-8ft in the Ments, 6ft+ at Nias while South Sumatra should see sets above 8ft early.

Winds will become variable from the eastern quadrant around Nias and the Ments while increasing E/SE trades are due around South Sumatra.

A further drop in swell is due Saturday, but into Sunday the easing trend will be halted as a new inconsistent S/SW groundswell fills in. This swell is being generated by a strong but weakening cold front pushing into WA and should keep exposed spots in the Ments topped up with 5ft sets, with larger 6ft bombs in South Sumatra.

From here on though the swell will drop away and bottom out through the second half of the week, with super exposed spots only likely to offer very inconsistent 2ft to maybe 3ft waves Friday. Winds will remain generally favourable and variable for the Ments, with fresh E/SE trades through Wednesday and Thursday in South Sumatra.

Next weekend onwards (Sep 6 onwards)

The next significant increase in swell is due later Sunday the 7th of September but more so Monday as a new node of the Long Wave Trough strengthens slightly in the South-eastern Indian Ocean around the 2nd of September.

This should project a couple of strong polar fronts up towards us, generating a couple of pulses of good S/SW groundswell, the first for Monday morning in the inconsistent 6ft+ range in the Ments, while a secondary pulse is likely sometime Wednesday/Thursday in the 6ft range at exposed spots.

Beyond this, looking at the super long term we may see a really strong node of the LWT strengthening in the South-western Indian Ocean around the 10th of September and this would bode well for large swell into the middle of September but we'll review this again Tuesday.

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