tradewinds is a genereic term for the most common wind in a given area, they can range from 10kn to 40kn depending on where you are, generally tropical trades in that area blow nw or w in season but are quite weak in the small latitiudes ie 0 deg to 8 deg due what they call the tropical convergence zone. so do your research, go to a weather site that shows you past wind observations and averages for that area then youll know!! by a big kite!! and a light wind board!!! maybe. good luck
Check a web site called wetsands, they have a surf report that you can look at all over the world and see the wind and swell directions. But I dont think you will get any averages, you will probably need to contact the BOM in where ever your going