Did a search here on seabreeze and the original question was asked a couple of years back (2009)
Anyone been over to Samoa since then ?
Reports ?
Conditions ?
Potential ?
Scotty McKercher and some of the StarBoard crew were over a few years back but didn't score the right conditions... anyone know if they went back ?
Pretty consistent trade winds according to WindGuru and HEAPS of reef breaks all the way round the islands 
logan, luke and the boys are there now, surf trip, ask them when they get back in a week or so.
It's listed in the "World Kite and Windsurfing Guide" and reads as follows:
Pros
- Pacific Island Paradise
- Super-consitent groundswell
- World-class waves
- Authentic culture
Cons:
- Light winds
- Sharp, shallow coral reefs
- Rudimental telco facilities
They also mentioned something about certain areas prohibit surfing on Sundays. The guide lists June / July as the best months for wind... 45% 15 knts+. Apparently the surf rarely is below 3 meters but almost every spot has ultra shallow reefs requiring a high tide to be on the safe side.
I think the "light winds" point could be an issue. Better take your new 100 liter quad. 
Sailed a yacht there a few years back, spent around month cruising mostly along the south coast of the main island. Surfed heaps. Trades were very light (<15knots) the whole time which I think is the norm as its a fair way north and nearly out of the trades belt. My understanding is for strong trades you need to be in a compression zone above a large high. This zone is more intense south of Samoa. Fiji and Tonga get really strong consistent trades in my experience. But its worth noting there is usually a cycle that takes about 10 days to repeat as the high moves through, only 4-6 days of those would be 18knots plus i reckon. So if your going on a windsurf trip to a mid ocean island in the trades go for 10 days at least!
