If you were using Google-earth for the calculation, as I did two weeks ago, you will notice that the flight plan "flat line" and the flight plan "at altitude (35,000 ft or 10,670 m)" is somewhat slightly moving to the west, making a 2.68 NM separation from the "flight plan center line".
Hi, Takata. I didn't used Google (btw, I don't believe it is strict conformal mapping).
I used the official coordinates of the waypoints, the BEA published position received at 0210Z (2.98, -30.59) and Sodano's formulas witch are, I remember reading somewhere, the recommended formulas to use with navigation computers and WGS84.
About satellite weather images, I just understand they are no to be taken as snapshots, so I won't imply anything unless I learn more. However, I think we can see on your map where the following LH flight crossed through the storm.
DJ