[AugustH]

NOAA explicitly warns against interpolating currents between stations:

• Currents are spatially variable, thus predictions should NOT be extrapolated even to nearby locations. Interpolation between two nearby locations should NOT be attempted. Use of such extrapolations can be hazardous.(emphasis is theirs)[/list:u]
  
  Unless there is a flow model available that describes mathematically how the currents vary over time, it's impossible to take isolated stations and create a chart that accurately reflects the currents. The programs listed in the other posts must use very simple models, or the areas they cover are simple enough (not changing that dynamically over time) that they can form predictions based upon limited data. This is my speculation, though, as I have not looked at them.
  
  For example, up here in the San Juan Islands the currents are incredibly complex. The Canadian Fisheries service produced a book with about 90 separate images of what the currents do, based upon the tide height at a station and how long ago the high tide occurred. The images show currents that reverse flow in a short space, flows that spiral, and flows that change velocity dramatically over one hour. Modeling something like this requires hours of computer time, not something that we simple users can do.
  
  Look at this example and you can see why current vectors are something neither Richard nor I want to even get close to: