Nias, Mentawai, South Sumatra forecast by Craig Brokensha (issued Thu 31st Jul)

Best Days: Every day over the coming period

This Friday and weekend (Aug 1 – Aug 3)

After a good pulse of S/SW groundswell yesterday, a slow drop in size should be occuring through today and then further into tomorrow and Saturday, bottoming out into the evening.

Into Sunday a very acute S'ly (even a touch S/SE) swell is due across south facing breaks, generated as far east in our swell window as you can really get, just under the south-west tip of WA.

As a result South Sumatra will see the most size to 6ft at exposed south facing breaks during the morning, while the Ments are expected to see 5ft sets with smaller surf towards Nias.

Winds should be variable around Nias over the coming days with moderate E/SE trades around the Ments and fresh SE trades in South Sumatra.

Next Monday onwards (Aug 3 onwards)

Monday's large and powerful SW groundswell is still on track. This swell is being generated south-east of Madagascar by back to back polar frontal systems, with the second broader front working on the active sea state created by the first.

This second front should continue west towards WA while weakening into tomorrow leaving a long-range, but strong and large SW groundswell to travel towards us, arriving through Monday, building strongly during the day and peaking overnight.

The Ments should build to 8ft to possibly 10ft on dark with the odd bigger bomb possible in South Sumatra and a touch less size around Nias.

A slow drop in size is due through Tuesday and further into Wednesday morning, but a reinforcing S/SW groundswell is due into the afternoon and Thursday, generated on the backside of the progression responsible for Monday's increase.

This should push exposed breaks back to 6ft the the chance of the odd 8ft bomb Thursday around the Ments, 6-8ft+ in South Sumatra and 6ft+ around Nias.

Winds will become variable in South Sumatra through next week, but further north a less than favourable moderate NW'ly is likely across the Ments with weaker winds around Nias.

Longer term there's nothing major on the cards until mid-week the following week, but we'll look at this again Tuesday.

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