Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Thu 24th Jul)

Best Days: Every day besides tomorrow

Friday onwards (Jul 25 onwards)

Small to moderate and inconsistent levels of S/SW groundswell have padded out the last couple of days, and a similar pulse is due this afternoon before backing off into tomorrow.

Of greater importance is two fresh pulses of SW groundswell, the first being smallest, arriving through Saturday and peaking into the evening. This will be followed by a secondary much larger and more powerful swell through Sunday, peaking through the afternoon.

The first swell was generated by a quick-fire front south-east of South Africa and set up an active sea state for a secondary much larger and stronger polar front to move over the last few days.

A peak to an inconsistent 6ft Saturday afternoon/evening is expected before holding a similar size Sunday morning ahead of the secondary pulse. This swell should peak at 8ft at exposed spots in the Ments, with the possibility for rare 10ft sets. South Sumatra will see more consistent sets in the 10ft range, while Nias will probably max out at 8ft or so.

The swell is expected to dip away through Monday and only drop a touch through Tuesday from 6ft+ or so around the Ments.

Winds in general are expected to tend variable through the weekend with light to moderate NW winds into early next week (possibly less favourable from the W/NW around South Sumatra Sunday afternoon and Monday).

Wednesday's large S/SW groundswell has been downgraded a touch with the polar front generating the swell not expected to be as strong or intense as forecast Tuesday and instead just inconsistent but still large S/SW side-band energy is due through Wednesday to 6ft+ at the most exposed south facing breaks in the Ments. South Sumatra will see more size to 6-8ft or so.

Into the end of the week, another S'ly groundswell is due Friday evening and Saturday morning, but the intense polar storm generating this swell will fire up late in our swell window and generate an acute S'ly groundswell for our region.

This swell should be stronger than Wednesday's and offer 6ft to occasionally 8ft sets at exposed spots, with noticeably smaller surf around Nias and bigger 8-10ft waves around South Sumatra at it's peak. From here on an easing trend is due ahead of some new swell through the week starting the 4th of August, but more on this Tuesday.

Coming back to the winds through the second half of next week and they should tend variable again across most spots, but the Nias region may see a moderate NW'ly into the end of the week and following Saturday.

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