I put my voltage meter on the fan and it gave a current about 5mv at maximum speed
Below is what I observe on my scope when spinning the fan manually (no power).
It peeks at about 2V and will go higher if I use more force. Frequency suggests I'm able to spin it manually to about 50-100 RPM. With this signal it would be possible to measure "wind" force - at least from an interface/electrical perspective (e.g. using analog to digital sampling).
Whether the fan is suitable for this purpose is another story. There is quite some inertia so light "winds" would be an issue. Also I'm not sure how it would stand up to the elements. If I wanted to gauge the suction of my vacuum cleaner however I think it could work quite well.