That is the beauty of a Hobie Island... you can use the boat in zero wind to higher wind speeds. Hard for me to advise using the boat in conditions that exceed the local small craft advisory levels (they do vary by region and body of water type).
The problem with wind is that it can vary greatly by location on the same body of water. Shoreline angles or hills / mountains can bend, decrease or increase wind. You can only get an approximate speed from a local station.
I like weather underground. They have good readings and lots of history data for many areas.http://www.wunderground.com/
Also... this graphic can help you see speed and directional changes in areas: http://hint.fm/wind/