Hi Robert,
Thanks for the response. Yeah that clears things up now and I can see how that works. New Zealand does have a site with similar maps on it called MetVuw, although it has the land outline and text on the map too, so when it comes to reclassifying it becomes a bit messy. Also, there is no georeference file, so the python script won't be very useful.
However, I'm going to built a model to bring in Metvuw images.
Thanks for your help
Shaun